Migratory Fishes
of South America

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Migratory Fishes
of South America

Biology, Fisheries and Conservation Status

EDITED BY
JOACHIM CAROLSFELD
BRIAN HARVEY
CARMEN ROSS
ANTON BAER

International Development Research Centre
Ottawa • Cairo • Dakar • Montevideo • Nairobi • New Delhi • Singapore

World Fisheries Trust
204–1208 Wharf Street, Victoria, BC, Canada V8W 3B9
http://www.worldfish.org • info@worldfish.org

The International Bank for Reconstruction and Development / The World Bank
1818 H Street, N W, Washington, DC 20433 USA
http://www.worldbank.org • feedback@worldbank.org • Tel: 202-473-1000

International Development Research Centre
PO Box 8500, Ottawa, ON, Canada K1G 3H9
http://www.idrc.ca / • pub@idrc.ca

© 2003 The International Bank for Reconstruction and Development / The World Bank

The findings, interpretations and conclusions expressed herein are those of the author(s) and do not necessarily reflect the views of the Board of Executive Directors of the World Bank or the governments they represent.

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National Library of Canada Cataloguing in Publication Data

Migratory Fishes of South America : Biology, Fisheries and Conservation Status / edited by Joachim Carolsfeld . . . [et al].

Co-published by IDRC and the World Bank.
Includes bibliographical references.
ISBN 0-9683958-2-12

1. Fishes—Migration—South America. 2. Fishes—South America. 3. Fisheries—South America. 4. Fishery conservation—South America.
I. Carolsfeld, Joachim, 1955- II. International Development Research Centre (Canada) III. World Bank. IV. World Fisheries Trust

QL632.A1M53 2003       333.95’6’098       C2003-906143-4

Design and production by Alaris Design, Victoria, Canada
Printed in Canada

TABLE OF CONTENTS MIGRATORY FISHES OF SOUTH AMERICA

LIST OF CONTRIBUTORS

Angelo Antonio Agostinho

Núcleo de Pesquisas em Limnologia, Ictiologia e Aqüicultura (Nupelia), Depto. de Biologia

Universidade Estadual de Maringá

Ave. Colombo, 5790

Maringá, Paraná, Brazil

CEP 87020-900

E-mail: agostinhoa@wnet.com.br

Ricardo Alvarez-León

Departamento de Ciencias de la Vida, Instituto de Humanidades y Ciencias Básicas

Universidad de La Sabana

Bogota, Colombia

E-mail: alvarez_leon@hotmail.com

Carlos A. R. M. Araujo-Lima

Instituto Nacional de Pesquisas da Amazônia (INPA)

C.P.-478; 69011-970

Manaus, AM, Brazil

Email: calima@inpa.gov.br

Joachim Carolsfeld

World Fisheries Trust

#204-1208 Wharf Street

Victoria, BC, Canada

V8W 3B9

E-mail: yogi@worldfish.org

Jaime Alberto Diaz-Sarmiento

Centro de Investigaciones Científicas, Universidad de Bogotá

Jorge Tadeo Lozano Cr 4a, No. 22-61

Apartado Aerea 314185

Bogotá, Colombia

E-mail: jaime.diaz@utadeo.edu.co

Horácio Ferreira Júlio Jr.

Núcleo de Pesquisas em Limnologia, Ictiologia e Aqüicultura (Nupelia), Depto. de Biologia Celular e Genética

Universidade Estadual de Maringá

Ave. Colombo, 5790

Maringá, Paraná, Brazil

CEP 87020-900

E-mail: hfjulio@nupelia.uem.br

Hugo P. Godinho

Graduate Program on Vertebrate Zoology, Pontifical Catholic University of Minas Gerais

Av. Dom José Gaspar, 500

Belo Horizonte, MG, Brazil

CEP 30535-610

E-mail: hgodinho@pucminas.br

Luiz Carlos Gomes

Núcleo de Pesquisas em Limnologia, Ictiologia e Aqüicultura (Nupelia), Depto. de Biologia

Universidade Estadual de Maringá

Ave. Colombo, 5790

Maringá, Paraná, Brazil

CEP 87020-900

E-mail: lcgomes@nupelia.uem.br

Brian Harvey

World Fisheries Trust

#204-1208 Wharf Street

Victoria, BC, Canada

V8W 3B9

E-mail: bharvey@worldfish.org

Emiko Kawakami de Resende

Empresa Brasileira de Pesquisa Agropecuária (Embrapa), Embrapa Pantanal

Caixa Postal 109

Corumbá, MS, Brazil

79320-900

E-mail: emiko@cpap.embrapa.br

Mauro Luis Ruffino

ProVárzea – MMA/IBAMA/PPG7

Rua Ministro João Gonçalves de Souza

s/nº; 69.075-830

Manaus, AM, Brazil

Email: ruffino@argo.com.br

Yoshimi Sato

Estação de Hidrobiologia e Piscicultura de Três Marias

Companhia de Desenvolvimento dos Vales do São Francisco e do Paranaíba (CODEVASF)

Três Marias, MG, Brazil

E-mail: cvsf3m@prgressnet.com.br

Uwe H. Schulz

Fish Ecology, Universidade do Vale do Rio dos Sinos (UNISINOS)

Centro 2, 93022

São Leopoldo, RS, Brazil

E-mail: uwe@cirrus.unisinos.br

Harumi Irene Suzuki

Núcleo de Pesquisas em Limnologia, Ictiologia e Aqüicultura (Nupelia)

Universidade Estadual de Maringá

Ave. Colombo, 5790

Maringá, Paraná, Brazil

CEP 87020-900

E-mail: harumi@nupelia.uem.br

Evoy Zaniboni Filho

Departamento de Aqüicultura/CCA, Universidade Federal de Santa Catarina

Caixa Postal 476 – Campus Universitário – CEP 88040900

Florianópolis, SC, Brazil

E-mail: zaniboni@cca.ufsc.br

ACKNOWLEDGEMENTS

The preparation of this book was funded by the World Bank and the International Development Research Centre (IDRC). The editors and authors would like to thank M. Isabel Braga and Robert Schneider of the World Bank’s Latin America and the Caribbean Environmentally and Socially Sustainable Development Unit for their enthusiasm and encouragement, and IDRC’s Brian Davy for his unfailing dedication to small-scale fisheries in the developing world. The Canadian International Development Agency is also to be thanked for facilitating the networking needed to keep the team of authors together over the several years it took to produce this book.

1
INTRODUCTION
Fishes of the Floods

Brian Harvey
Joachim Carolsfeld

World Fisheries Trust

Victoria, BC, Canada

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TABLE OF CONTENTS CHAPTER 1

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The Idea Behind this Book

In 1996, the World Bank published Freshwater Biodiversity in Asia, with Special Reference to Fish, a technical review that has become a sourcebook for anyone interested in Asian migratory fish species.¹ The need for a companion volume on South American species was obvious, especially in a historical moment where the precarious status of inland water biodiversity was finally beginning to get the international attention it deserved. We approached the Bank, fortunately at a time when new and forward-looking ideas about water management were beginning to appear in its own reports and guidelines, and our proposal for a book on South America species, by South American authorities, was enthusiastically received. As biologists who had worked for many years with these species, both for conservation and for culture, we knew enough to side-step the task of writing the story of the migratory species ourselves – in Brazil alone, which takes up much of this book, the number of major river basins is so great, and the variety of species, life histories and lives affected so staggering, that no single author could do the subject justice. Fortunately, the region is blessed with fisheries scientists of very high calibre, and with interests broad enough that we were able to assemble a team of authors who covered most of the major river basins in Brazil, as well as the Colombian portion of the Amazon Basin. In some cases the authors worked alone; in others, their chapter is a team effort. In all cases, they were writing about their own back yards.

We believe that the material these authors provided, and which we have tried to assemble in a coherent whole, represents the first time the experience of so many local experts has been tapped and brought together to illuminate the lives of the remarkable migratory species of South America for an international audience. And there is much more here than just a wealth of biological detail. There are description of the rivers and the specific habitats the fish live in; there is discussion of the many and varied fisheries for the most important species; our authors list the threats

¹ Kottelat & Whitten, 1996

to maintaining the fish as a sustainable resource, or, in many cases, threats to a species’ very survival; they describe the legal and legislative instruments used to manage the fish; and finally each author provides a prescription for improving how these very special fish are understood and managed.

In our instructions to authors we were adamant that they describe not only the fish, but also their social importance, because the fishes’ lives intersect with the lives of people at every turn, and the business of the World Bank, who commissioned this book, is in development for people. We believe that that admonishment has paid off in a volume that will be of great interest not only to other biologists, but to managers, policy makers, community groups and conservationists as well. In the final analysis, the more development is informed by understanding of the ecosystems it affects, the better the chances of that development being truly sustainable. As instigators and editors of Migratory Fishes of South America, we sincerely hope that we are contributing to that process.

Important but Ignored

The migratory fish species of Latin America are a well-kept secret. However great their biological and cultural importance, outside their native range they are known only to biologists with a special interest in the tropics, and to the occasional especially intrepid sport fisherman or aquarist. Many people know about salmon and their prodigious migrations from the ocean to the place of their birth many kilometers upstream, but few outside South America have ever heard of the dourado or the surubim, species every bit as charismatic as salmon. True, some migratory species, like pacu and tambaqui, are farmed in Asia and the southern United States, and juveniles of these species are popular aquarium fish. But the farmed products have yet to catch on in a big way, and the baby fish grow up to be too large, and too unlovely, to keep.

But pacu and tambaqui and several dozen other large species have life histories every bit as awe-inspiring as the salmon’s. Some of them migrate more than a thousand kilometers to spawn, and unlike the salmon they do it year after year. More important, the South American migratory species feed people too, and provide them with recreation, and have a place in the hearts of Latin Americans that is every bit as important as the

iconic role played by salmon in North America and Europe. Migratory species have always been mainstays of subsistence and small-scale commercial fisheries, feeding into distribution networks that put surubim from the Amazon onto dinner plates in São Paulo and Brasilia. In the past decade these species have also stimulated the explosive growth of sport fishing that pulls in visitors not only from neighbouring cities but also from as far away as Japan and Russia.

This book is a comprehensive look at the lives, and the social importance, of the principal migratory freshwater fish species of large river systems in South America. It is unusual in several ways. First, it is written by leading Brazilian and Colombian fish biologists. Second, it covers a vast geographic area, including the Brazilian and Colombian Amazon, Paraná-Paraguay, São Francisco and Uruguay basins. Finally, it describes not only the state of current knowledge of the migratory fish species in each basin, but also their importance as food for local people.

It must be pointed out that the definition of “migratory” can be broad and varied.² Moreover, the species discussed by the authors of this book are by no means the only migratory ones in the rivers. The book concentrates on economically important species that appear to conduct obligatory reproductive migrations – in other words, those that spawn only after migrating between two distinct geographical areas. This definition of migratory fish is the one commonly accepted in Brazil, and is practical in that it identifies a group of fish that are clearly affected by alterations to their migratory routes. Most of these same species, as well as other species in the rivers and reservoirs, also carry out migrations between habitats for feeding and refuge, but these migrations are quite varied and appear to be more or less opportunistic. Evidence for and interpretation of this distinction varies between the river basins and authors, and in the present book is seen most strikingly in Chapter 7 on the Colombian Amazon.

However, there are species of less direct economic value and/or smaller body size, such as forage fish, that are migratory too. For example, sardinhas (Pelota spp.) are reported to lead the reproductive migratory subienda in the Upper Amazon (see Chapter 7), fishermen in the Mogi Guaçu (Upper Paraná River Basin) speak of migratory species of the

² Lucas & Baras, 2001

lambari (Astyanax spp.) that lead the piracema in this river (unpublished). Small forage species leaving the flood-plain lagoons as they drain are the defining characteristic of the lufada phenomenon of the Brazilian Pantanal that coincides with the first stage of the reproductive migration of larger and economically important species. While these species are of obvious ecological importance, very little is known about them and they are not generally the targets of directed fisheries. They are not covered by most of the authors in this book.

Migratory Strategies: Endless Variety

There is a staggering variety of migratory species in Latin America, and their life histories are incredibly diverse. The characids have scales. Some, like the dourado Salminus, look salmon-like. The big catfish, the pimelodids particularly prized for their flesh, are smooth-skinned. The diets of the two groups range from mud to fruits to other fish to plankton, and the spawning journeys they embark on every year, when the rains come and the rivers overflow their banks into the wetlands and forests, are bewilderingly various. Some species go upstream to spawn, while some go downstream. Some spawn in headwaters above the flooded areas of the Pantanal, the world’s largest wetland, while others release their eggs in the rivers mainstem. A few have even managed to carry on reproducing despite the existence of numberless reservoirs that spatter the map of Brazil and testify to the colossal scale of hydroelectric development in the country. All of them, however, release their eggs to the currents, where they drift, and hatch, and feed with the rhythm of the rising and falling waters, coming and going from habitats that appear and disappear with the floods.

Readers of this book will be introduced to a group of fishes that has evolved a variety of strategies for using the transient habitats that result from the seasonal floods characteristic of the region. Floodplains and inundated forests are essential for larval and juvenile development of most of these species, and provide foraging opportunities once they have become adults. Most of the species depend absolutely on the cues associated with flooding, for it is these cues that trigger reproduction.

Migration is a spectacular phenomenon, with the shoals of adults heading upstream making a memorable picture. In larger rivers the system

is particularly complicated, with adults and juveniles travelling not only up and down the river mainstem, but also in and out of the tributaries and their associated floodplains. Some species travel more than 1000 km, at speeds up to 16 km per day.³ Migrations that go up and down river channels (both mainstem and tributaries) are usually called “longitudinal”, while “lateral” migrations are those between the channel and the floodplain – although local terminology sometimes complicates the picture further.

The migratory strategies themselves vary between species and river basins. If there can be said to be a general pattern for reproductive migrations, it is an upstream spawning migration (piracema or subienda), followed by a downstream dispersion of eggs, larvae and spent adults into floodplain areas. However, there are many variations on this theme, with the most complex situation being in the Amazon, where there can be at least three separate phases of migration, with adults migrating both up and downstream, for reproduction or for feeding, in tributaries and in the mainstem river. Another variant occurs in the Upper Uruguay, where floodplains are less common and juvenile development takes place in the transient environments found at the mouths of tributaries backed up by flooding of the main river channel (in Chapter 4 the terms “longitudinal” and “lateral” are even used differently from the usual convention). The passive downstream drift of larvae and juveniles is common to most migratory patterns in South America, in contrast to salmon in North America, for example, where fry control their own movement downstream in response to developmental and environmental cues.

If a river is large enough there may even be separate upriver and downriver populations of a single species, which makes unravelling their migration patterns that much more complicated. Even today, drawing a simple diagram of a migration pattern for a given species, in a given river system, is difficult, because such a diagram requires detailed information on movements and genetic makeup that is in most cases lacking. The descriptions of migratory patterns provided by each of the authors in this book represent the best knowledge currently available, but they will undoubtedly be refined in the years to come. The new tools of DNA fingerprinting (to distinguish between separate populations of the same species) and radio-tagging (to track fish movement) are only now

³ Welcomme, 1985

beginning to be applied in Brazil, and it is over the coming decade of research that we will finally be able to draw the migration maps so necessary for sustainable management. Such tools, and the picture of migration patterns they can provide, are doubly important when one considers the effects of changing flow patterns, water extraction, and damming. Different species react to obstacles differently; some of them can negotiate fish ladders, and others may be able to establish separate populations in the smaller sections of river available to them after a dam is erected, or even spawn in a reservoir. In the absence of good data on migration, the true effects of these alterations to habitat can only be guessed at.

Apart from general similarity of reproductive patterns, many of the most abundant characid migratory species, which represent up to 70% of the fish biomass in South American freshwaters, share a dietary dependence on detritus or the fruit and vegetation of terrestrial plants, with only larval phases relying on plankton. Carnivorous migratory characids and catfish in turn prey on these fish, transferring nutrients between habitats and relying on seasonal input from inundated terrestrial areas. All these migratory species share the unfortunate attribute of being very poorly understood – a point that is made time and again by the authors of this book.

Threats to Migratory Fishes

Like inland water biodiversity everywhere, the freshwater fishes of Brazil and Colombia are faced with a variety of threats. The migratory species, because of their wide-ranging habits, are probably the most vulnerable group of all, and the fact that these species provide food and income for local people makes their situation doubly significant.

Threats to migratory fishes in South America include industrial, domestic, and agricultural pollution, deforestation, alteration and obstruction of river flows, introduced species and overfishing. While all basins experience all of these threats, pollution is particularly severe in parts of the Paraná and Uruguay rivers, damming is especially intense in the Upper Paraná and the São Francisco rivers (many of the rivers in South America are so heavily dammed as to have become a chain of reservoirs), and overfishing is evident in parts of the São Francisco, Paraná,

and Amazon systems. Gold mining causes heavy metal pollution in the Upper Paraguay and in the Colombian and Brazilian Amazon. Large-scale works including dredging and pipelines have the potential for widespread habitat damage in the Paraná-Paraguay region. Pollution from hog and poultry farming is a special problem on the Upper Uruguay, and the use of herbicides to eradicate illegal crops has serious consequences for fishes in the Colombian Amazon. Pollution has left the Piracicaba River, which drains into the Paraná, biologically depleted and in some sections devoid of aquatic life. Exotic species like the tucunaré, an Amazonian native introduced to the Paraná and Paraguay basins, may confer economic benefits (for example, as commercial and sport fish) but compete for habitat and food with several native migratory species. Riverside deforestation has the unexpected effect of eliminating a food source for species that live on fruits and seeds borne to them by the river. Even climate change is potentially disastrous because it affects the rhythm of the waters, and for species that live and die with the annual flood, water is everything. Migratory fish populations appear currently to be healthiest in portions of the Amazon and Upper Paraguay basins.

An idea of just how vulnerable the migratory species are can be gained from an analysis published by Froese and Torres (1999). These authors used the data in FishBase, a large database on finfish, to analyze the biological characteristics of threatened fish species contained in the 1996 IUCN Red List. The result is nothing less than a profile of the kind of fish most likely to become extinct. Here are the characteristics of the unlucky winner:

• Freshwater (ten times higher threat than to marine fish).
• Migrates to spawn or feed.
• Feeds at lower trophic levels.
• Large, slow-growing and late-maturing.
• Doesn’t guard its eggs.
• Occurs in countries with high population densities.
• Occurs in areas where there are many introduced fish species.

As a description of many of the migratory species of South America, the above list could hardly be improved on; for readers of this book, the following chapters will introduce species after species that fits the description.

Fisheries

Fisheries on South American migratory species are classified as subsistence, sport, and commercial. The latter are carried out primarily for domestic markets, with the only significant “industrialized” export fisheries being in the Amazon. Subsistence fisheries generally use simple gear. Fisheries vary in importance in different basins: the Amazon currently contributes 54% of all documented Brazilian freshwater fisheries production, including aquaculture. The industrialized Amazonian fishery is based on only a few catfish species, whereas the subsistence, artisanal and sport fisheries utilize many species in all basins. Sport fishing is especially important to the economy of the Pantanal in the Upper Paraguay, but is also significant, and growing, in most other locations. Subsistence and commercial artisanal fishing are also becoming increasingly important for riverine communities in most basins, as access to agricultural land and other sources of income decreases.

Depletion of fish stocks (not necessarily by overfishing) is leading to conflict between sport and artisanal fishing groups in all basins, a conflict that is closest to resolution in areas of the Amazon where community-based management is practised, and in the Lower Pantanal. Throughout the region, managers are having to confront the different needs of the commercial and sport groups, both of which have different requirements of the resource. Greater inclusion of stakeholders in management will help, and is starting to happen, but the need for better monitoring of stocks and catches will not go away.

This book makes the ambitious attempt to categorize and describe the several kinds of fisheries in each basin and on each major species. In so doing the authors, despite their location in the basins themselves, faced a daunting task. Although inland waters are now generally accepted to support a huge variety of small fisheries with enormous significance for local livelihoods, any analysis of these fisheries is presently crippled by the lack of good reporting and statistics. The basins are vast, the people who catch fish are strung out along mainstems and tributaries, central landing sites are the exception rather than the rule, and the most one can confidently say about catch statistics is that they’re underestimates. Whether this means the fisheries are over-extended or actually healthier than is now believed is anyone’s guess.

Management of fisheries in the absence of reliable statistics is like minding a store with no record of sales and no inventory. Coates (2002) has analyzed the situation in Asia, where under-reporting of inland fisheries is the rule. In the eight countries he reviewed for FAO, Coates found that inland capture fisheries were under-reported by factors ranging from four to as high as twenty-one. A similar analysis of fisheries statistics for South America and the implications for management is urgently needed. For now, all we have is warning flags such as Araujo-Lima and Ruffino’s note on catch reporting in the Brazilian Amazon (page 221), “the total catch from the Amazon may be as much as three times the values presented by IBAMA.” If, as we suspect, the same situation obtains in other basins, conservation and sustainable management of the migratory species in South America are presently being hobbled by the most basic of needs – the need for information.

Geographic Coverage and Aliases

The geographic coverage of South America by this book is not complete, and several major systems with important migratory species are excluded. The Orinoco River (Colombia and Venezuela), for example, like the Amazon arises on the eastern Andes and drains large tracts of rain forest and tropical savannahs before flowing into the Caribbean. Another major river not covered here, the Magdalena (Colombia), drains the moist central valleys of the northern Andes. The Parnaíba River (Brazil) drains arid lands and its relatively small discharge flows into the Atlantic between the Tocantins and the São Francisco rivers. The Essequibo River of Guyana is the largest of the three major rivers in Guyana. None of them are covered in this book. Several of them cross or form international boundaries, which leads to complicated issues of exploitation and conservation, especially when the river flow is altered. The Yacyreta Dam, a huge bilateral project on the Paraná River that is shared between Argentina and Paraguay, is a good example, as is the Itaipu Binacional on the border between Brazil and Paraguay.

Because this book is a collection of chapters, each one written by a different group of authorities, there is inevitably some overlap. Most obviously, many of the species occur in several or all of the six river basins.

Just how much overlap there is in species composition, and how many and varied are the aliases each goes by, can be seen at a glance in Appendix A. These tables show that their status, the threats they face, the kinds of fisheries on them and even their common names may be different in different places.

South America is just too big, and its geography and social ecology too varied, to allow a one-size-fits-all description of the life and times of pintado or tambaqui. Hence we have not only allowed repeated description of certain species, we in fact consider it one of the book’s strengths. This way, each chapter is as complete as the author can make it, and for readers whose interests go beyond a single river basin, encountering the same fish in two different places will be like running across an old friend and looking out for changes since the last meeting.

The reason so many species inhabit geographically separate basins, of course, relates to the prehistory of the continent. Because the Amazon River originally drained into the Pacific, then into the Caribbean (through the present-day Magdalena River), and then into the northern coast of South America (through the present-day Orinoco River), many of the fish species in the different river systems are the same.⁴ Present-day conditions developed from the rise of the Andes, starting about 89 million years ago. Studies of mitochondrial DNA, for example, suggest close genetic relationships between the Prochilodus species in the Paraná, Amazonas, Orinoco, and Magdalena basins.⁵ Since so many of the same species occur in different basins, and because so many basins cross national boundaries, it should be no surprise that certain migratory species pose unique management problems. The sábalos (Prochilodus spp.) and the large catfishes (for example, Pseudoplatystoma spp.), both of which migrate extensively, are prominent examples of this problem.

The Migratory Fishes as Examples of Freshwater Biodiversity

The contribution of inland waters to the global economy and local livelihoods is under-appreciated, and the migratory fish species are just

⁴ Lundberg et al., 1998

⁵ Sivasunder et al., 2001

one part of a complex web of inland biodiversity. Despite their relative insignificance in terms of area (less than 0.5% of the world’s water), inland waters contain 40% of all aquatic species. And, largely because of the “captive” geographic nature of inland waters that makes them so susceptible to habitat degradation, freshwater fish species by far outnumber marine ones on the current IUCN Red List (84% freshwater). Freshwater species face special risks, of which fishing is certainly not the greatest, yet they are less well known than marine ones. Those risks are not just the familiar ones of habitat loss and pollution – the impact of global warming on water levels will be profound, and for a group of species like the migratory fish whose biology is completely evolved around the ebb and flow of floodwaters, the implications are enormous.

One of the results of the shortage of information on global taxonomy is that it’s difficult to compare the numbers of migratory and non-migratory South American species. In the one basin where guesses have been hazarded, namely the Amazon, estimates hover around 3,000 fish species and would seem to relegate the forty-six migratory species described by Araujo-Lima and Ruffino (Chapter 6) to part of a distinct minority. Incomplete identification of species, and deficient fisheries landing statistics, make it impossible to be more precise in this or any other South American basin.

Of course, the South American species are not the only migratory fishes in the world. Although the patterns are often different from those seen in South America, migration is a prominent feature of the lives of a huge variety of fish species in other parts of the world, and the effects of damming and redirecting rivers have been especially singled out for study. A cursory look at some of these species (in North America, Europe, Asia and Africa) is provided in Appendix B. For species in South America, Africa and Asia the exhaustive review by Welcomme (1985) is highly recommended.

The Future

What is the future for the migratory fishes of South America? There is no simple answer, in large part because of the vast geographic area over which they are spread, and the great differences in status, use, and especially the

political and bureaucratic structure of local management systems. One certainty, however, is that the general lack of data is unlikely to change without better international awareness of these remarkable species. The migratory fish described in this book need to be promoted at home and on the world stage, in scientific meetings and in the popular media. As the profile of inland waters struggles upward, migratory fishes need to be more visible, and so do the communities that depend on them. Governments cannot be expected to push for research and management reforms for an obscure target. We hope this book will be the beginning of such an awareness.

The authors of each section offer their own detailed recommendations for conservation and management of the South American migratory fishes in their respective basins. Common elements of these recommendations are:

• Specifically and urgently address problems created by damming rivers, by regulating new development to ensure that floodplains remain accessible above reservoirs, improving fish passage, and developing water flow management protocols that re-instigate seasonal flooding patterns in downstream river sections. Several authors (although by no means all) recommend an improved stocking program for reservoirs in their area that includes monitoring of effectiveness and impacts;
• Reduce pollution, deforestation, floodplain destruction, and agricultural impact, including, in the case of Colombia, the use of herbicides to combat illicit agriculture. All authors felt that existing regulations could address many of the problems of environmental degradation, but that enforcement needs to be improved and that public education is an essential element in effecting that improvement.
• Improve knowledge of the migratory fish species, including better documentation of how they are affected by pollution, habitat loss, alterations of flow and overfishing;
• Implement fisheries management programs that accommodate the various interest groups in their development. In the Amazon, community-based management is recommended. Where a basin is shared between countries, as in the Paraná-Paraguay and Colombian

Amazon, authors stress the need for co-ordination amongst neighbouring countries. Both the Amazon authors and the Upper Paraná authors emphasize that agencies must consider more carefully the social implications of management regimes;

• Revise and implement broader biological survey and fisheries monitoring programs.

A Note on Usage

The authors use the terms “fisherman” and “fisher.” While men do most of the fishing in the areas described in this book, women are heavily involved in processing, maintenance and marketing (see for example Nordi’s first-hand description of fishing on the São Francisco River, page 175). The fact that most current dictionaries have no entry for “fisher,” and define “fisherman” as “a person who catches fish,” indicates how unsettled the terminology is, so we have elected to allow the individual authors their preferences.

REFERENCES

Coates, D. 2002. Inland capture fishery statistics of Southeast Asia: current status and information needs. Asia-Pacific Fishery Commission, Bangkok. RAP Publication No. 2002/11. 113 p.

Froese, R., and A. Torres. 1999. Fishes under threat: an analysis of the fishes in the 1996 IUCN Red List. In Pullin, R. S. V., D. M. Bartley and J. Kooiman (Eds.). Towards policies for conservation and sustainable use of aquatic genetic resources. ICLARM Conf. Proc., 59:131–144.

Kottelat, M., and T. Whitten. 1996. Freshwater biodiversity in Asia, with special reference to fish. World Bank Technical Paper No. 343. World Bank. ISBN: 0-8213- 3808-0

Lucas, M. C., and E. Baras. 2001. Migration of freshwater fishes. Blackwell Science Ltd, Oxford. 420 p.

Lundberg, J. G., L. G. Marshall, J. Guerrero, B. Horton, M. C. S. L. Malabarba, and F. Wesselingh. 1998. The stage for Neotropical fish diversification: a history of tropical South American rivers. In Malabarba, L. R., R. E. Reis, R. P. Vari, Z. M. S. Lucena, C. A. S. Lucena (Eds.). Phylogeny and classification of Neotropical fishes. EDIPUCRS, Porte Alegre, Brazil. 13–48 p.

Sivasundar, A., E. Bermingham, and G. Ortí. 2001. Population structure and biogeography of migratory freshwater fishes (Prochilodus: Characiformes) in major South American rivers. Molecular Ecology, 10:407–418.

Welcomme, R. L. 1985. River fisheries. FAO Fisheries Technical Paper 262. Food and Agriculture Organization of the United Nations. Rome.

2
MIGRATORY FISHES OF THE
Upper Paraná River Basin
Brazil

Angelo Antonio Agostinho
Luiz Carlos Gomes
Harumi Irene Suzuki
Horácio Ferreira Júlio Jr.

Núcleo de Pesquisas em Limnologia, Ictiologia e Aqüicultura (Nupelia)

Universidade Estadual de Maringá

Maringá, Paraná, Brazil

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TABLE OF CONTENTS CHAPTER 2

CHARACTERISTICS OF THE BASIN

Geography and Geology

The Paraná River is formed by the junction of the Grande and Paranaíba rivers in south-central Brazil, and flows into the Rio de la Plata in Argentina. It is the tenth longest river in the world (4,695 km) and has a 2.8 x 10⁶ km² drainage area that includes most of the south-central part of South America (18^o to 34^o S; 45^o to 68^o W) from the Andes to Serra do Mar near the Atlantic Ocean (Figure 1). The Upper Paraná River includes approximately the first third of the Paraná River Basin, and lies completely within Brazilian territory, except for a stretch within the Itaipu Reservoir,

FIGURE 1. Map of the Upper Paraná River Basin showing location of principal dams

which borders Paraguay. The Upper Paraná River Basin has an area of 891,000 km² or 10.5% of the total area of Brazil. The river flows south-southwest, through the region of the greatest population density in Brazil. The climate in the Upper Paraná region is tropical/sub-tropical, with an annual average temperature of 15^oC and more than 150 cm precipitation per year.⁶

The two rivers that form the Paraná River begin in the central plateau and run through sedimentary and volcanic rocks of the Paraná and Chaco sedimentary basins, which are bordered on the eastern side by the highlands of the Andes and on the north and east by the Precambrian rocks of the Brazilian Shield.⁷

River Profile

The rivers that form the Paraná River are similar to other plateau rivers, with an average slope of 0.8 m per km, decreasing in the middle portion to 0.3 m per km.⁸ The Upper Paraná River floodplain stretches from the Porto Primavera Dam to the upper part of the Itaipu Reservoir. This 230 km stretch is not dammed, and drops 0.2 m per km. This floodplain, especially on the western margin, may reach up to 20 km in width. Here the Paraná is braided with an accumulation of sediments in its channel forming sandbars and small islands, and a few large islands. The complex anostomosis in this stretch involves secondary channels, the Baia River and lower parts of tributaries on the western margin (Ivinheima, Amambai, and Iguatemi rivers). On the eastern margin, the main tributaries are the Tiête, Paranapanema, Ivai, Piquiri and Iguaçu rivers (Figure 1).

Water Uses

In São Paulo State the estimated urban demand for water is 87 m³/s, with 50% returned to rivers. Only 8% of this water receives treatment. Industrial water demand in São Paulo State is 113 m³/s, with 68% returned to rivers. The demand for the irrigation of around 470,000 ha is also great.⁹ Ever increasing demands for water for human consumption, agriculture and

⁶ IBGE, 1990

⁷ Petri & Fulfaro, 1983

⁸ Agostinho et al., 2000

⁹ CERH-SP, 1990

cattle, the intense use of pesticides and fertilizers and the removal of riparian vegetation have all worsened water quality in the main tributaries and in the Paraná itself.

Dams are the most common signs of human interference on the physiography of the region. Over time there has been a steady increase in the inundated area.¹⁰ Dams are present in all major tributaries (Grande, Paranaíba, Tietê, and Paranapanema rivers) and in the Paraná main channel as well. There are more than 130 major reservoirs in the region (dam > 10 m high); among these, 20% are larger than 10,000 ha. Four are in the Paraná main channel and range in area from 48,200 to 225,000 ha. The first large reservoir, the Edgard de Souza Reservoir on the Tietê River near the city of São Paulo, was formed in 1901. However, 80% of the reservoirs in the Upper Paraná River were built after the 1960s¹¹.

Habitats Used by Migratory Species

Three types of habitats are needed by migratory fish to complete their life cycles in the Upper Paraná Basin. They are:

Spawning habitats

The spawning habitats, in general, are in the upper parts of large tributaries of the Paraná. Vazzoler et al. (1997a) showed this in two tributaries (Piquiri and Ivinheima rivers), where the number of reproducing individuals and eggs increased towards the upper parts of the main tributaries (Figure 2). Observations of fish spawning in the Upper Ivinheima River indicated that Characiformes prefer shallow water (less than 3 m), of relatively narrow width (less than 80 m) and usually with moderate turbulence. The river bed is usually rocky or of sand/gravel, and spawning takes place during floods, when water is turbid and conductivity and temperature are high. Although some Siluriformes spawn in similar habitats (for example Rhynodoras dorbigny and Hemisorubim platyrhynchos), most prefer the less lotic water and sandy bottoms of the Lower Ivinheima River.¹² Other species were found reproducing exclusively in the main channel of the Paraná (Paulicea luetkeni, Piaractus mesopotamicus).

¹⁰ Agostinho et al., 1995a

¹¹ Agostinho et al., 1995a

¹² Vazzoler et al., 1997a; Nakatani et al., 1997

FIGURE 2. Frequency of reproductive individuals, egg density and designation of spawning areas in different portions of two tributaries of the Upper Paraná¹³

Nursery habitats

Nursery habitats are generally lagoons in the lower parts of the tributaries and along the Paraná River banks and islands. These lagoons are heterogeneous in shape, area, mean depth, and degree of connection with the river. Drifting larvae reach these lagoons when the river overflows. Later, when the water is receding, fry may actively enter the lagoons through the remaining channels. Results from several habitat studies of the Upper Paraná floodplain suggest that lagoons are the environments richest in diversity of phytoplankton, periphyton, rotifers, aquatic macrophytes, benthos and fishes; the greatest abundance of phytoplankton, zooplankton, aquatic macrophytes and fishes is also observed here.¹⁴ During high water, when the lagoons are deeper, thermal stratification may persist for more than 24 hours, leading to vertical stratification of nutrients and gases¹⁵ and, frequently, anoxic layers close

¹³ Modified from Vazzoler et al., 1997a

¹⁴ Agostinho et al., 2000

¹⁵ Thomaz et al., 1992; Lansac-Tôha et al., 1995

to the sediment.¹⁶ During low water, complete mixing of the water column occurs during the night or morning when the lagoons are usually shallower than 2 m.¹⁷ Despite low levels of dissolved oxygen in the lower water layers, lagoons provide a profusion of shelter and food for fish fry.

Feeding habitats

Feeding habitats are places used for feeding by adult fish along the Upper Paraná, its tributaries and reservoirs. These habitats can be classified as the Paraná River channel, meandering rivers, rapid rivers, secondary channels, the Itaipu Reservoir, and small streams and creeks.

The bottom of the Paraná River channel, in the stretch free from dams (between downstream Porto Primavera Dam and upstream Itaipu Reservoir), is sandy or arenitic, and of low declivity. There are more than 300 islands and numerous sandbars, with a maximum water depth of 30 m. The main tributaries are meandering or rapid rivers.

Meandering rivers are located on the western margin of the Paraná. They have low slope, sandy bottoms, and, in general, are short (less than 400 km long). Springs in the sedimentary basin give rise to the Ivinheima, Iguatemi, and Amambai rivers.

Rapid rivers are located in the eastern margin, have high slopes, rocky bottoms, and are long (more than 400 km). Springs in crystalline rocks of the Serra do Mar give rise to the Piquiri, Ivai and Iguassu rivers.

Secondary channels are a net system (anostomosis) composed of the lower part of the tributaries on the western side of the Paraná and channels that connect the floodplain to the river. Substrate in the secondary channels is sandy or muddy. Discharge, flow direction, and limnological conditions depend highly on the flood regime and on the water level differences between the effluent basin/lagoon and the Paraná.

The Itaipu Reservoir marks the southern limit of the migratory fish populations in the unimpounded stretch of the Paraná. This reservoir is 150 km long, with an area of 1460 km², an average depth of 22 m, a hydraulic retention time of 40 days, and limnologically acts as a warm mesotrophic and monomictic water body.¹⁸ In its upper third, because of the influence of the Paraná, processes of transport predominate. Here it

¹⁶ Thomaz, 1991

¹⁷ Thomaz, 1991; Lansac-Tôha et al., 1995; Paes da Silva & Thomaz, 1997

¹⁸ Agostinho et al., 1994a

is possible to catch all the migratory species, but most of them are low in abundance. Some species such as Pterodoras granulosus, Rhaphiodon vulpinus, Prochilodus lineatus and Rhinelepis aspera are very common in the reservoir and are important to the artisanal (or “professional”) fisheries.

Small streams and creeks, more conspicuous on the eastern side of the river, vary highly in gradient, substrate, size, proportion of riffles to pools, cover, and conservation of riparian vegetation. Juveniles of long-distance migrators may be observed only near the mouth of these systems (less than 5 km), and in low abundance. Only juveniles of Leporinus obtusidens, Pimelodus maculatus and P. lineatus have been recorded in creeks.

MIGRATORY SPECIES AND MIGRATION PATTERNS

As in other river basins of Brazil, fish surveys in the Upper Paraná remain incomplete and controversial. The 221 fish species registered to date may become as many as 300 once the many taxonomic questions are resolved.¹⁹ Information on aspects of ecology exists for only 86 of the 221 described species. Only 16 of these 86 species generally travel over 100 km in their migrations to reproduce. Of the remaining 70 species, some migrate moderate or short distances to reproduce (Figure 3).

These migratory species depend directly on upstream migration to complete the development of their gonads and to spawn. They fertilize externally, migrate long distances, and show no parental care. Generally they are large fishes (maximum standard length > 40 cm) with seasonal and total spawning, small eggs and high fecundity.²⁰ Winemiller (1989, 1992) calls these species “periodic strategists”.

In addition to reproduction, other reasons for migration may include: temperature, feeding, ontogenetics, growth, refuge and avoidance of adverse environmental conditions. These factors may overlap and be dependent on one another,²¹ but all are in some way related to the flood pulse.²² The hydrological cycle is synchronised with biological events such as gonad maturation, migration, spawning and larval development,

¹⁹ Agostinho & Júlio Jr., 1999

²⁰ Suzuki, 1992

²¹ Bonetto, 1963

²² Bonetto & Castello, 1985

* Short distance migrants migrate less than 100 m

FIGURE 3. List of species in the Upper Paraná River Basin according to migratory behaviour and reproductive strategy

growth and feeding²³ and a close relationship exists between recruitment success and the time, duration and intensity of floods.²⁴

Distribution

Surveys since 1982 have reported adults and juveniles of migratory species in diverse habitats in the Upper Paraná Basin. Most of the large migratory fishes occur throughout the basin. P. luetkeni, P. mesopotamicus and R. aspera primarily inhabit the main channel of the Paraná, reservoirs and major tributaries. Other species, such as Salminus hilarii and Steindachneridion sp., prefer lotic habitats in minor tributaries. Among these five species, Steindachneridion sp. is the least abundant and is

²³ Gomes & Agostinho, 1997; Agostinho & Júlio Jr., 1999; Agostinho et al., 2000

²⁴ Gomes & Agostinho, 1997

considered rare.²⁵ P. granulosus and R. vulpinus, on the other hand, are now widely distributed in the Upper Paraná, but came originally from the middle and lower parts of the basin, colonising the upper stretches after the Itaipu Dam (in 1983) inundated a natural barrier (Sete Quedas Falls). These two species are not however present in upstream rivers where dams were built before 1982.

A longitudinal gradient has been reported for eggs and larvae of large migratory fishes, from the upper to the lower parts of tributaries of the Upper Paraná (Figure 4).²⁶ Eggs were more frequent in the upper reaches and larvae in the lower. This trend was verified in all large rivers of this part of the Paraná Basin, providing evidence for the presence of spawning areas in the upper portion of the river and nursery areas in the lower portion.

Feeding

Among 16 migratory species, information on diet exists for the 13 most common species (Table 1).²⁸ Information on the feeding of S. hilarii, P. luetkeni, and Steindachneridion sp. is inconclusive. Some of these species are naturally rare or live in habitats difficult to sample, such as rapids (Steindachneridion spp.) or at great depths (P. luetkeni).

FIGURE 4. Longitudinal gradient of egg and larval densities of migratory fishes in the Ivinheima River, a tributary of the Upper Paraná²⁷

²⁵ Agostinho et al., 1994a

²⁶ Nakatani et al., 1997

²⁷ Nakatani et al., 1997

²⁸ Hahn et al., 1997; Agostinho et al., 1999a

TABLE 1. Dietary habits and principal food items of migratory fish from the Upper Paraná River Basin²⁹

²⁹ Agostinho et al., 1995; Hahn et al., 1997, Agostinho et al., 1997

Among the migratory species, six have been identified as piscivores (Salminus maxillosus, Pseudoplatystoma corruscans, R. vulpinus, H. platyrhynchos, P. luetkeni and Pinirampus pirinampu). S. hilarii and Steindachneridion spp. can be added to this category based on the analyses of stomach contents³⁰ and gut morphology. Piscivores usually include the larger fish in the basin and also compose the most preferable group of fish in the commercial fisheries in the Upper Paraná. Some piscivores, such as H. platyrhynchos and P. pirinampu, are not as specialised in relation to their food intake. They may include plant and other non-fish groups in their diet; however, fishes composed at least 90% of the diet.

Five species were identified as omnivorous (P. granulosus, Leporinus elongatus, L. obtusidens, P. maculatus and P. mesopotamicus) feeding on plants, molluscs, aquatic insects and other invertebrates. Most of these feed opportunistically and may be interpreted erroneously as specialists when studies are conducted in restricted environments where some food items that may be taken as food are abundant. Before the Corumbá Dam closure, L. elongatus and P. maculatus were herbivorous and omnivorous, respectively, with a tendency to insectivory. After the dam closed and the reservoir began filling, L. elongatus was classified as omnivorous, with a tendency to piscivory and P. maculatus as piscivorous.³¹ P. mesopotamicus is now rare in the Upper Paraná. Considered a frugivore in the Amazon Basin³², it eats plants and insects in the Upper Paraná.³³

Growth

Studies on growth of neotropical inland fish species are not numerous,³⁴ but are important information for fisheries management. Data on growth of migratory species in the Upper Paraná are limited to four species (P. lineatus, P. maculatus, R. vulpinus and R. aspera). Two further species (P. corruscans and S. maxillosus) were studied in other regions of the basin (Table 2). The maximum lengths registered for other species in the Upper Paraná are also listed in Table 2. P. luetkeni is the heaviest fish in the basin and may grow up to 150 kg.

³⁰ Agostinho, unpublished data

³¹ Agostinho, unpublished data

³² Goulding, 1980

³³ Hahn et al., 1997; Agostinho et al., 1997

³⁴ Lizama & Vazzoler, 1993

TABLE 2. Maximum total length and reproductive characteristics of migratory fish from the Upper Paraná River Basin³⁵

³⁵ Suzuki, 1992; Agostinho et al., 1995a, 1995b; Vazzoler et al., 1997a, 1997b; Nakatani et al., 2001

Abundance

Surveys to assess the fish population abundance in different parts of the basin have included impounded stretches, such as in the Grande³⁶, Corumbá³⁷, Tietê³⁸, Paranapanema³⁹ and Iguaçu⁴⁰ rivers. The unimpounded segment of the Paraná and unimpounded tributaries were also sampled.⁴¹ Nupélia-Uem/Itaipu Binacional monitors landings of artisanal fisheries, useful for assessing the abundance of fishes, in the Itaipu Reservoir. The Companhia Energética do Estado de São Paulo and Furnas Centrais Elétricas collect the same information in other reservoirs of the Upper Paraná.

In impounded upper stretches of the Paraná migratory species are absent from, or sporadic in, experimental and artisanal fisheries. Two exceptions are P. lineatus and P. maculatus, which are found where there is a free-flowing stretch of river above a reservoir or where a large tributary empties into a reservoir.

Large migratory fishes are the second most abundant group in the stretch of river between Itaipu Reservoir and Porto Primavera Dam, including the floodplain and main tributaries, contributing 21% of the total catch.⁴² In general, the abundance of migratory fish fluctuates according to flooding intensity and duration. The floodplain of the Upper Paraná, sampled for four years under different flood intensities, revealed that two of the years (1985–1987) were dry (low or absent floods) and the other two (1992–1993) were wet (high water levels). The abundance of most migratory fish was greater in the wet year.

Migratory species contributed 39–57% of the total catch to artisanal fisheries in the Itaipu Reservoir between the 5th and 17th year after dam closure (Figure 5). Among the ten most important species in the fishery, seven use the lotic environments upstream to reproduce,⁴³ where important unimpounded tributaries and a wide floodplain exist. Natural

³⁶ Santos, 1999

³⁷ FUEM-Nupélia-Furnas, 1999

³⁸ CESP,1996

³⁹ Dias, 1995; CESP, 1996

⁴⁰ FUEM-Nupélia-Copel, 1998

⁴¹ Benneman et al., 1995; Agostinho et al., 1997

⁴² Gomes & Agostinho, 1997

⁴³ Agostinho, 1994

and artificial variations in the flood regime over the floodplain are the main causes of changes in migratory species abundance.⁴⁴

In the Iguaçu River, an important tributary of the Paraná, large migratory fishes are absent, with the exception of Steindachneridion sp., a large pimelodid restricted to the lower river. The fish fauna in the Iguaçu River evolved in a fluvial scenario. The river was fragmented by waterfalls and isolated from the remaining Paraná Basin by the Iguaçu Falls, formed approximately 22 million years ago. Fragmentation by waterfalls is considered the main cause of the fish fauna isolation and further speciation through time, resulting in high endemism in headwaters.⁴⁵ The absence of large migratory fishes that are common in other parts of the basin was used as an argument that the construction of five dams in the Iguaçu River would have little impact.⁴⁶ However, studies in Segredo Reservoir demonstrated that most of the species migrate short distances, entering small tributaries or reaching the fluvial zone of the reservoir to reproduce.⁴⁷ Similar behaviour is reported for non-migratory species in other reservoirs in the Upper Paraná Basin.⁴⁸

FIGURE 5. Annual yield of the artisanal fishery of the Itaipu Reservoir⁴⁹

⁴⁴ Gomes & Agostinho, 1997; Veríssimo, 1999

⁴⁵ Sampaio, 1988; Severi & Cordeiro, 1994; Garavello et al., 1997; Agostinho et al., 1997

⁴⁶ Agostinho et al., 1999c

⁴⁷ Suzuki, 1999

⁴⁸ FUEM-Nupélia-Itaipu Binacional, 1999; FUEM-Nupélia-Furnas, 1999

⁴⁹ Agostinho et al., 1994b; Petrere et al., 2002; Agostinho, unpublished data

Migration Patterns

Migration plays an important role in reproductive success because it promotes the meeting and high concentration of both sexes in an area appropriate for egg fertilisation, development (high oxygenation) and low predation (low water transparency). Fish migration is therefore bound to the adequacy of the environment for the eggs and the advantages of collective spawning and the simultaneous releases of enormous numbers of gametes, thus improving fertilisation and chances of egg survival.

Tagging experiments in the Mogi Guaçu River revealed that some species migrate more than 1000 km.⁵⁰ Similar studies in the Paraná channel showed displacement in the order of 450 km for P. lineatus.⁵¹ Figure 6 shows the ascending movements of P. lineatus starting from the Itaipu Reservoir. Individuals captured downstream and released in the reservoir were recaptured 180 km above it.⁵² However, in an 80 km lotic stretch of the Paranapanema River between the Capivara and Salto Grande reservoirs, fifteen years after the construction of the dam schools of the migratory S. maxillosus and P. corruscans are still found during the reproductive period.⁵³ These results suggest that migratory fish populations vary widely in their requirements for a home range, depending on the species.

In the lower stretch of the Upper Paraná (230 km long), where the incoming tributaries are not impounded, populations of all the migratory fishes are still found. Three of these species (P. lineatus, R. vulpinus, and L. obtusidens) are among the most abundant in the region. In floodplain habitats the abundance of adults varies seasonally. Sixteen species that were restricted to the Middle Paraná before the Itaipu Dam was built expanded their range into the Upper Paraná after the Sete Quedas Falls were submerged in the reservoir.

⁵⁰ Godoy, 1975

⁵¹ Agostinho et al., 1993a

⁵² Agostinho et al., 2002

⁵³ João Henrique Pinheiro Dias, personal communication

FIGURE 6. Movements of P. lineatus tagged at the Itaipu Dam, Santa Teresinha, São João do Itavó and Guaira⁵⁴

Spawning

In the Upper Paraná, as in other tropical floodplain rivers, the flood pulse is the primary factor in fish reproduction. Monitoring of migratory fishes spawning at the Cachoeira das Emas, Mogi Guaçu River (Figure 1) from

⁵⁴ Agostinho et al., 2002

1943 to 1970 demonstrated that flooding is important as a synchronizing cue for spawning, and that lotic water is fundamental to oocyte fertilisation, fluctuation and drifting.⁵⁵

All the migratory species considered in this study are broadcast spawners (external fertilisation without parental care) and generally show total spawning, releasing all of the oocytes at the same time. Migratory fishes may shed a great number of eggs – from 52,000 by P. maculatus to 2,600,000 by S. maxillosus – in fast-moving waters, in which the water movement facilitates gamete mixing and fertilisation. Hydration increases egg volume up to four times⁵⁶ and reduces specific weight, prompting flotation and drifting. In slow-moving water, however, even hydrated eggs sink. Hydrated eggs drift along the river, under conditions of increasing water level, and spill over onto the floodplain. There they complete their development as the larvae hatch and are carried onto the flooded area. Some species, such as R. aspera, although a broadcast spawner, release eggs, which after 10 or 15 minutes become adhesive and attach themselves to a substrate.

Synchronisation of spawning with periods of rain, when water levels begin to rise, is frequently mentioned in the literature.⁵⁷ Godoy (1975) reported that large migratory fishes do not spawn when the river water level is stable or falling. Other authors also mention this dependence. In monitoring young of the year (YOY) in temporary lagoons in the Upper Paraná floodplain, a complete absence of YOY of large migratory species during years without floods was reported.⁵⁸ There was also a positive correlation between the duration and timing (season) of the flood in the Upper Paraná floodplain and P. lineatus recruitment in the Itaipu Reservoir, located downstream of the floodplain.⁵⁹

For species with similar reproductive strategies, Agostinho et al. (2001) used the annual average CPUE (catch per unit effort) of individuals with ripe and/or semi-spent gonads as an indicator of reproductive intensities in years of different flood intensities in the Upper Paraná (1985–1987 were dry years, whereas 1992–1993 were wet years). The abundance of

⁵⁵ Godoy, 1975

⁵⁶ Godoy, 1975

⁵⁷ Godoy, 1975; Vazzoler & Menezes, 1992; Agostinho et al., 1995a, 1999a; Araujo Lima & Goulding, 1998

⁵⁸ Verissimo, 1999

⁵⁹ Gomes & Agostinho, 1997

most migratory fish was greatest in the wet years. In terms of reproductive activity (Figure 7), it was concluded that (i) among sedentary species, which include those that spend their entire life cycle on the floodplain,

FIGURE 7. Annual variation of the abundance of reproductive adult fish and young fish of different migratory strategies in the Upper Paraná River relative to the extent of flooding⁶⁰

⁶⁰ Agostinho et al., 2001; CPUE = catch per unit effort; 1986–87 = flood absent; 1987–88 = moderated flood; 1992–93 = normal flood

reproductive activity was greater during droughts; (ii) “reproducing” individuals among the long-distance migratory species were more abundant in the year of the highest flood; (iii) among short-distance migratory species, intermediary variation in abundance was verified. However, the abundance of juvenile forms was low for all the reproductive strategies in the floodless year, due to factors such as increased exposure to predation.⁶¹

Oocyte development up to, but not including, final maturation seems unrelated to hydrologic cycle. Gonads develop in ponds or even in some isolated lagoons, where they reach an advanced stage of maturation but undergo regression if no stimulus for spawning is registered. Vazzoler et al. (1997b) considers the increase of temperature and daylight as proximate factors related to the gonad maturation that, in general, occurs from August to November or December.

As size varies among the migratory fish species, so does size at first maturation (Table 2). For 25 species from the Upper Paraná, the size at first maturation is approximately 40% of the maximum length.⁶² Most of the migratory fishes analysed here reach first maturation at a proportionally larger size, from 45% to 55% of the maximum size registered. P. lineatus is an exception, reaching maturity at 36% of the maximum length (28 cm).

Reproductive Strategy

Besides high fertility, migratory fishes have small oocytes, short incubation times and small larvae (Table 2). Oocyte diameter varies little, ranging from 0.8 mm (P. maculatus) to 1.6 mm (Brycon orbignyanus). Other non-migratory fishes, especially those that develop parental care such as Hypostomus spp., have oocytes of more than 5.0 mm. Despite the bias arising from measuring eggs and oocytes preserved in formalin, hydration increases egg sizes by 42% (P. corruscans) to 170% (P. lineatus), except for eggs of R. aspera (just 11%), which do not float. Small eggs have a short incubation time and produce small larvae⁶³. Egg development times depend on mean temperature. This time ranges from 326 degree-hours

⁶¹ Agostinho et al., 2001

⁶² Vazzoler et al., 1991

⁶³ Balon, 1984

for L. obtusidens to 818 degree-hours for R. aspera, compared to more than 4,200 degree-hours for non-migratory fishes, such as those with parental care (Geophagus spp). Larval size is greater among non-migratory fish and among species that have large eggs such as Parauchenipterus galeatus, whose larvae hatch measuring 4.9 mm.⁶⁴ Oocyte diameter, incubation time, larval size and hydration are important adaptations that allow eggs to float and drift, and to reach the nursery areas in lower parts of the basin.

In general, migratory fishes are total spawners. However, oocyte development, in contrast to that reported for non-migratory species with total spawning, is not synchronous. From studies of oocyte development of P. lineatus in ponds, it was concluded that during maturation eggs initially develop non-synchronously in the ovaries.⁶⁵ As maturation proceeds, a synchronous grouping of eggs that will be shed simultaneously occurs. This kind of development was observed in other large migratory species (S. maxillosus and L. obtusidens) and in short migratory species (Astyanax bimaculatus, Apareiodon affinis and Leporinus friderici) and has been classified as “non-synchronous cumulative development”.⁶⁶ We believe that this type of oocyte development gives migratory fishes the flexibility to spawn when the appropriate environmental conditions appear.

Timing of Spawning

In the Upper Paraná Basin, migration and spawning occur between October and March, when flooding begins and peaks. Characiformes, in general, spawn earlier (Oct. to Jan.) than Siluriformes (Dec. to Mar.). Reproductive movements and spawning are rapid and their timing seems to be regulated by flooding. If the rain and flooding are delayed, most of the migratory species may start spawning in February. A failure of fish reproduction was reported⁶⁷ in the Upper Paraná as a consequence of the absence of flooding during the spawning season, despite the late increase in the river level (flooding from March to July).

⁶⁴ Nakatani et al., 1997

⁶⁵ Fenerich-Verani et al., 1984

⁶⁶ Suzuki, 1992

⁶⁷ Gomes & Agostinho, 1997

In the flooded areas, larvae and fry of migratory species find warm temperatures and ample food and shelter. As the water level drops, juveniles concentrate in floodplain depressions or swim out with currents into the main channel, where they search for lentic waters (bays and lagoons connected to the river). In general, juveniles inhabit these environments for a time that varies according to species. P. lineatus, for example, remains in these habitats for about two years.⁶⁸

During decreasing water levels, mortality of juveniles is high. There are three major causes: (i) predation where water is flowing out of the floodplain (vazantes or corixos); (ii) mortality in lagoons that dry up completely, and (iii) predation by birds, mammals or reptiles in very shallow water bodies. Duration, regularity and timing of the floods all contribute to these types of mortality and subsequent recruitment to the adult population.⁶⁹

After spawning, parental stock start returning downstream, but more slowly and by a sinuous route. They may go inside lagoons, apparently looking for food to replace energy lost in the migration upstream.⁷⁰

Spawning Sites and Migratory Behaviour

The minimum stretch required by migratory fish to complete their life history varies according to species and regional characteristics, and may even vary within the species itself. For example, parts of tagged schools of the migratory species P. lineatus and S. maxillosus remained for a long time where they were released in the Upper Paraná, suggesting that some populations of these species complete their life cycles without migrating, while others require long displacements upstream to maintain the population and spawn.⁷¹ In the last free stretch of the Upper Paraná, below Porto Primavera Dam and above Itaipu Reservoir that has been isolated from the upper and lower stretches since 1994 some migratory fish (S. maxillosus, P. corruscans, P. lineatus, L. elongatus, and B. orbignyanus) were found reproducing.⁷² However, not only the length of the stretch,

⁶⁸ Agostinho et al., 1993a

⁶⁹ Gomes & Agostinho, 1997

⁷⁰ Bonetto & Castello, 1985; Agostinho et al., 1993a

⁷¹ Bonetto & Castello, 1985

⁷² Agostinho & Zalewski, 1995; Vazzoler et al., 1997a; Nakatani et al., 1997

but also its characteristics, such as the availability of spawning sites, and more importantly nurseries, are vital.

Agostinho et al. (1993a) studied the migratory behaviour of the curimbatá (P. lineatus) in a 380 km stretch of the Upper Paraná Basin, which included the Itaipu Reservoir and the unimpounded stretch upstream (Figure 8). Juvenile fish, up to the time of their first maturation

FIGURE 8. Conceptual model representing the behaviour of Prochilodus lineatus in the Upper Paraná River Basin (A) and environments used during its life cycle (B)⁷³

⁷³ Modified from Agostinho et al., 1993a

at age two, live in floodplain lagoons. They then migrate during flooding via the anastomosing floodplain channels to the main river, reach the main channel of the Paraná, and are finally recruited to the stock in the Itaipu Reservoir.

Neotropical migratory fishes seem to have less need to return to historical spawning sites than do salmonids. In the Piquiri River, upstream from Sete Quedas Falls (inundated by the Itaipu Reservoir), no schools of P. lineatus and S. maxillosus had been registered before the formation of Itaipu Reservoir. After the filling of the reservoir, schools inhabiting the 170 km downstream from the mouth of the Piquiri River started to use the river as a spawning ground.⁷⁴ The distribution of eggs and larvae of different species collected in the Upper Paraná Basin suggests that schools may enter different affluents simultaneously to spawn.⁷⁵ After the closure of Porto Primavera Dam (in the main channel of the Paraná) fish tagged during upstream migration and released downstream were recaptured 48 hours later in a tributary on the western margin, 40 km from where they were released. This suggests that during upstream migration, an obstacle may lead the fish to search for another place. However, histological examination of these fish showed a high frequency of atresic oocytes in the ovaries, indicating that if spawning occurred it would be less effective.⁷⁶ An intense regression in gonads of fish was also registered during the spawning season immediately below the Itaipu Dam.⁷⁷

Details of the migration patterns of most of the other species, especially the big catfishes (P. corruscans, P. luetkeni and P. pirinampu) are still unknown. It appears nonetheless that flooding is also important in stimulating their migration and spawning. Complete understanding of these mechanisms, differences between species, and requirements for critical spawning and nursery areas require more study.

Description of Principal Species

The migratory fish species in the Upper Paraná Basin consist primarily of fish with scales belonging to the Characiformes and fish without scales

⁷⁴ Agostinho et al., 1993a

⁷⁵ Nakatani et al., 1997

⁷⁶ Agostinho, unpublished data

⁷⁷ Agostinho et al., 1993b

belonging to the Siluriformes (catfish). Figure 3 lists species according to migratory behaviour and reproductive strategy. Principal species are described below, with maximum and maturation lengths summarized in Table 2.

Brycon orbignyanus

B. orbignyanus is a medium-sized characid known as piracanjuba in Brazil and salmón criollo in adjacent Spanish-speaking countries. The Brazilian name is derived from the native tupi-guarani language, referring to the fish’s distinctive yellow head (pira= fish; acanga= head; yuba= yellow) and the Spanish name refers to the salmon-like pink colour of the fish’s flesh. The meat is of excellent quality for human consumption and is much sought after.

The species was once common in the basin, but is now captured only sporadically in the fisheries of the Paraná River, and seems to be virtually absent in the upper⁷⁸ and lower⁷⁹ stretches. About 40 years ago, individuals of up to 80 cm (8 kg) were caught, but more recently the maximum size has been 63 cm.

The fish is omnivorous, with a preference for fruits and other plant parts. Insects and small fish are considered secondary in the diet.⁸⁰ However, in the stretch of the Paraná River without dams, where it is fished with hooks using fruit as bait, it is mainly insectivorous, with plants as secondary items.⁸¹ The species is nevertheless strongly dependent on alloctonous food items⁸² and reduced numbers have been attributed to the removal of riparian vegetation by agriculture, cattle ranching and damming in the basin. In the Itaipu Reservoir, the species was caught only during the first 14 months after reservoir formation, and in other reservoirs it is rare.⁸³

Size of first maturation in the species is 30cm (2–3 yrs of age), with peak reproductive activity in December and January.⁸⁴ Ovaries at this time constitute more than 20% of body weight, with more than 850,000 oocytes

⁷⁸ Agostinho & Julio Jr, 1999

⁷⁹ Quirós, 1990

⁸⁰ Schubart, 1943; Godoy, 1975

⁸¹ Hahn et al., 1997

⁸² Godoy, 1975; Lowe-McConnell, 1986

⁸³ Agostinho et al., 1994b; CESP, 1996

⁸⁴ Vazzoler et al., 1997a

per individual (mean diameter of 1.5 mm). However, with annual variation in the hydrologic cycle, spawning may occur from October to January.

Duration and intensity of floods are important in determining recruitment of this species. Our unpublished data show that fry of B. orbignyanus were abundant in months that followed the intense and long-lasting floods of 1983–84, 1990–91 and 1997–98, but were rare when floods were moderate or absent (1985–86; 1995–96; 1996–97).

The species is of considerable interest to aquaculture, so most of the current publications on the species are devoted to this topic, particularly dealing with nutritional aspects.⁸⁵

Hemisorubim platyrhynchos

H. platyrhynchos is a medium-sized catfish commonly known in Brazil as jurupoca. It is the only species of this genus and is widespread within South America, from the Orinoco to the Paraná rivers. The snout is flattened and the back is brown, with elongated or oval dots along the body. In some environments the colour changes to yellowish brown on the back. It grows up to 63 cm, and is a nocturnal piscivore, feeding in lotic and lentic habitats. The first maturation is reached at 30 cm and spawning occurs in December and January, including November in some years, during the flood period. Ecology of the species is unknown, with publications dealing primarily with morphological and parasitological aspects.⁸⁶

Leporinus elongatus

L. elongatus, known in Brazil as piapara, is a medium-sized characid (maximum length = 61 cm) that reaches first maturation at 27 cm. It is of moderate abundance in the dams-free stretch of the Paraná River, primarily occurring in the main channel of this river, but is also caught in the upper parts of the Paraná River Basin.⁸⁷ Juveniles are found in marginal lagoons of the river. Artisanal and sport fisheries target this species, and in cities along the Paraná River bank fishing tournaments for piapara are common.

⁸⁵ e.g. Esquivel et al., 1999; Garcia et al., 2000; Cavalcanti et al., in press.

⁸⁶ Pavanelli & Rego, 1989; Lundberg et al., 1991; Chambrier & Vaucher, 1999

⁸⁷ Santos & Formagio, 2000

Early studies considered the species essentially herbivorous.⁸⁸ However, recent studies in the Upper Paraná River indicate that the species is omnivorous, feeding primarily on insects.⁸⁹ Changes in diet after alteration of the environment have been documented in the Corumbá River (a tributary of the Paranaiba River). The piapara in this river was apparently a herbivore, with a tendency towards insectivory, before the construction of the Corumbá Dam, but after dam closure and the formation of the reservoir, turned to omnivory with a tendency to piscivory.⁹⁰

Spawning of the piapara occurs in the upper stretches of large tributaries during December and January, when the water level in the river is rising. During this period, ovaries represent up to 25% of the body weight and have more than 1.8 million oocytes of 1 mm mean diameter.⁹¹ L. elongatus were second only to P. lineatus amongst migratory species in successful ascents of an experimental fish ladder at Itaipu Dam.⁹²

This species is also a good aquaculture candidate, and most of the published information about it is related to cultivation in ponds.⁹³

Leporinus obtusidens

L. obtusidens, popularly known in Brazil as piavuçu (pi’au=spotted skin, uçu=big in the tupi-guarani language) or piapara, is smaller than its congener L. elongatus (maximum length = 49 cm) and reaches first maturation at a smaller size (25 cm). It has moderate abundance in the basin, but is restricted to stretches with intact floodplains. It is frequent in lotic habitats but also occurs with moderate frequency in lagoons, thus differing from L. elongatus. Its preference for semi-lotic habitats is demonstrated by its abundance in meandering rivers like the Ivinheima and Iguatemi.⁹⁴ Juveniles live in marginal lagoons. Artisanal fisheries and weekend anglers target L. obtusidens in rivers, generally using hook baited with fruit (Cecropia sp.). Its importance for the fisheries in the Paraná River led the hydropower companies to stock the fish in reservoirs of the

⁸⁸ Godoy, 1975

⁸⁹ Hahn et al., 1997

⁹⁰ Gaspar da Luz et al., in press

⁹¹ Godoy, 1975

⁹² Fernandes, 2000

⁹³ Godinho & Santos, 1996; Sato et al., 2000

⁹⁴ Agostinho & Julio Jr, 1999

basin. However, except for the fluvial zone, L. obtusidens avoids reservoirs, and no data are available to evaluate the efficiency of the stocking programs.

Piavuçu is omnivorous, eating mainly plants and some insects, but may also feed on small fish, algae and detritus.⁹⁵ Spawning occurs from November to January, when gonads represent up to 18% of the body weight.

Little information is available about the biology and ecology of this species. Publications deal with nutrition of the fry,⁹⁶ condition factor,⁹⁷ cytogenetics⁹⁸ and semen characteristics.⁹⁹

Paulicea luetkeni

P. luetkeni, known in Brazil as jaú (ya-ú =big eater in the native language), is the heaviest fish in the basin, growing up to 144 cm in length and 150 kg in weight. In both the Paraná River¹⁰⁰ and the Amazon River¹⁰¹ the fish carries out its whole life cycle in the main channel, sheltering primarily in deep areas as adults and in the mouth of creeks and other small tributaries as fry. Unlike other migratory species, fry of the species have not been found in marginal lagoons and channels of the Paraná River. Almost absent in the upper regions of the Upper Paraná Basin, it was an important species in early landings of the artisanal fisheries in the Itaipu Reservoir. During this time, juveniles were captured in the reservoir and adults in the riverine zone. However, yield of this species has reduced drastically over the last decade, probably due to overfishing of smaller sized individuals and thus preventing adequate recruitment. In the dams-free stretch of the Upper Paraná, weekend anglers still target this species in the main channel, using hooks baited with worms.

P. luetkeni is a nocturnal piscivore and reaches first maturation with 70 cm total length. It spawns from December to February. Information about biology and ecology of this species is scarce, and most of this is related to nutrition of the fry,¹⁰² parasitology¹⁰³ or morphology¹⁰⁴.

⁹⁵ Hahn et al., 1997; Agostinho et al., 1997

⁹⁶ Mello et al., 1999

⁹⁷ Araya, 1999

⁹⁸ Jorge & Moreira Filho, 1996

⁹⁹ Kabeya et al., 1998; Murgas et al., 1999

¹⁰⁰ Agostinho & Júlio Jr., 1999

¹⁰¹ Santos & Ferreira,1999

¹⁰² Pelli et al., 2000

¹⁰³ Rego et al., 1986; Eiras et al., 1986; Rego, 1994; Takemoto & Pavanelli, 1994

¹⁰⁴ Lopes et al., 1994

Piaractus mesopotamicus

P. mesopotamicus, popularly known as pacu in Brazil (“fast eater” in the native language), grows up to 62 cm, reaching first maturation at 34 cm. Originally endemic to the Paraná-Paraguay River Basin, it is now more widespread in distribution through aquaculture activities. It was found only sporadically in experimental fisheries in the Upper Paraná River, but it is more abundant downstream of the Itaipu Dam and in the Ivinheima River. The species was stocked in several reservoirs of the basin, but with unknown results. It prefers lotic and semi-lotic habitats and, while omnivorous, depends strongly on allochthonous food items. Adults feed on plants and insects, whereas fry and juveniles feed on micro-crustaceans.¹⁰⁵ Anglers, however, use fruit as bait to catch the pacu.

Spawning of the pacu occurs from October to January.¹⁰⁶ The number of oocytes ranges from 59,000 to 426,700 per fish, according to the size of the fish, with an average diameter of the mature oocyte of about 1.4 mm.

A variety of information has been published on the species: it can tolerate temperature ranging from 15 to 35^oC, but does not feed below 18^oC;¹⁰⁷ it is reported to have an efficient pheromonal warning system for the presence of predators;¹⁰⁸ and it shows morphological and behavioural adaptations for survival under low oxygen conditions.¹⁰⁹ However, most of the studies on the species are on its artificial breeding,¹¹⁰ nutrition¹¹¹ and parasitology and pathology.¹¹²

Pimelodus maculatus

P. maculatus, a small catfish known in Brazil as the mandi, is widely distributed in the basin. It is abundant in rivers and the riverine zone of reservoirs, if the reservoirs have lotic stretches upstream or large lateral tributaries to spawn. The species needs less free river stretches than other migratory species, despite its ability to migrate more than 1000 km to spawn.¹¹³ Females grow to more than 45 cm in length, with first maturation at 20 cm.

¹⁰⁵ Hahn et al., 1997

¹⁰⁶ Ringuelet et al., 1967; Lima et al., 1984; Romagosa et al., 1998

¹⁰⁷ Milstein et al., 2000

¹⁰⁸ Jordão & Volpato, 2000

¹⁰⁹ Saint Paul & Bernardino, 1988; Severi et al., 1997; Rantin et al., 1998

¹¹⁰ Carolsfeld et al., 1988; Romagosa et al., 1990

¹¹¹ Canzi et al., 1992; Borghetti & Canzi, 1993; Macarin et al., 1994

¹¹² Boeger et al., 1995a; Pavanelli & Takemoto, 1995; Szakolczai et al., 1999

¹¹³ Bonetto, 1963; Godoy, 1967

The mandi is omnivorous, feeding on insects, molluscs, small fish, and plants.¹¹⁴ A tendency towards insectivory was recorded in the Corumbá River before the construction of the dam, but after the dam closure it was classified as a piscivore.¹¹⁵

The species spawns from November to January, with multiple spawning events during this period: a characteristic unusual for migratory species. It also possesses the smallest oocytes of migratory species (0.8 mm), which could be related to its success in reservoirs in that these may sink less quickly than the eggs of other species.¹¹⁶ The number of oocytes per fish was estimated at around 70,000 for a fish of maximum size.¹¹⁷ Other studies have been published on gonad maturation and reproductive cycle;¹¹⁸ biometry and sex dimorphism;¹¹⁹ induced spawning;¹²⁰ captive breeding;¹²¹ growth curve;¹²² and parasitology.¹²³

Pinirampus pirinampu

P. pirinampu is another medium-sized catfish known in Brazil as barbado, barba-chata, Patí, or mandi-alumínio. It has distinctive long band-like oral barbells with broad silvery membranous borders. The fish is widely distributed throughout the basin, including reservoirs in the Paraná River and its tributaries.¹²⁴ The abundance of the species in reservoirs increases toward the mouth of the Paraná, with the maximum abundance in the Itaipu Reservoir, where it is very important to artisanal fisheries in the riverine zone.

The fish grows to over 95 cm in length, with first maturation at 46 cm. It is caught by long-lines or hand-lines in impounded and unimpounded rivers with a special kind of fishing gear called the cavalinho. A cavalinho is a two meter-long trotline attached to a float with a single

¹¹⁴ Agostinho et al., 1997; Hahn et al., 1997

¹¹⁵ Gaspar da Luz et al., in press

¹¹⁶ Agostinho et al., 1999a

¹¹⁷ Godinho et al.,1977; Lamas, 1993

¹¹⁸ Godinho et al., 1974a, 1974b; Colares de Mello, 1989; Carvalho & Grassiotto, 1995; Bazzoli et al., 1997

¹¹⁹ Vignes et al., 1981; Barbosa et al., 1988

¹²⁰ Fenerich-Verani et al., 1984; Souza & Stiles, 1984

¹²¹ Sato et al., 1999, 2000

¹²² Fenerich et al., 1975

¹²³ Moreira et al., 1991; Petter, 1995a; Sato & Pavanelli, 1998, 1999; Gutierrez & Martorelli, 1999a, 1999b

¹²⁴ CESP, 1993; Agostinho & Julio Jr., 1999; Santos & Formagigio, 2000

hook baited with live fish. Fishers watch from canoes nearby for the float to bob to indicate a bite.

The barbado is a particularly aggressive piscivore species, with diurnal¹²⁵ and pelagic habits¹²⁶ not found in other pimelodid catfish. No information is available on its reproduction, other than that individuals with ripe gonads are caught downstream from the Itaipu Dam during December and January.

Studies on P. pirinampu are restricted to parasitology¹²⁷ and cytogenetics.¹²⁸

Prochilodus lineatus

Known as curimbatá in Portuguese and sábalo in Spanish, P. lineatus is the most studied fish species in the basin. It has a wide distribution, including rivers, lagoons and reservoirs.¹²⁹ Its abundance in reservoirs is correlated with the presence of free stretches upstream or large lateral tributaries. In unimpounded stretches of the Paraná River, recruitment is extremely variable according to the annual flood regime that is controlled by dams.¹³⁰ Adults live in running waters and juveniles in marginal lagoons. Juvenile P. lineatus can represent more than 70% of the biomass in lagoons after an intense and prolonged flood period, whereas when flooding is short and/or weak, they may be entirely absent.¹³¹

The species grows up to 78 cm in length and reaches its first maturation at 28 cm, based on a variety of studies on ageing and growth.¹³² It is iliophagous, feeding mainly during the day¹³³ and in shallow water¹³⁴ on detritus and sediments containing tiny particles of inorganic sediment, fine detritus and algae.¹³⁵ Food is taken from the bottom or from flooded vegetation,¹³⁶ with microorganisms in the detritus and periphyton an

¹²⁵ Hahn et al., 1997

¹²⁶ Agostinho et al., 1999a

¹²⁷ Kritsky et al., 1987; Rego & Pavanelli, 1992; Chambrier & Vaucher, 1999

¹²⁸ Swarça et al., 1999, in press

¹²⁹ CESP, 1993; Agostinho & Julio Jr, 1999; Santos & Formagio, 2000

¹³⁰ Gomes & Agostinho, 1997; Smolders et al., 2000

¹³¹ Agostinho & Zalewski, 1995; Veríssimo, 1999

¹³² Cordiviola de Yuan, 1971; Bayley, 1973; Toledo Filho, 1981; Hayashi et al., 1989; Domingues & Hayashi, 1998

¹³³ Hahn et al., 1997

¹³⁴ Lowe McConnell, 1975; Bowen, 1983

¹³⁵ Sverlij et al., 1993; Fugi et al., 1996

¹³⁶ Bowen, 1983

important nutrient source for the fish.¹³⁷ The fish has a significantly elongated intestine to deal with this kind of food source.¹³⁸ Based on studies of fatty acid composition, fry have diets based on zoo and phytoplankton, and detritus becomes gradually important as the fish grows.¹³⁹

Spawning occurs in running waters of upper stretches of some of the large tributaries of the Paraná River from October to January (as water levels rise). During this period, ovaries may represent more than 20% of the body weight, and contain up to 1.5 millions oocytes with a mean diameter of 1.5 mm. After fertilization and hydration to a diameter of 3.9 mm, the eggs drift in the river current during embryonic development and wash into the flood plains of the lower parts of the tributaries as the larvae hatch. The fish stay in the lagoons that remain as the flood water recedes for up to two years, or until their first maturation is complete.¹⁴⁰ The ready availability of food and shelter in the lagoons during the first months of life are essential to avoid high mortality rates from predation.¹⁴¹

Numerous studies have been carried out on the migration of the curimbatá.¹⁴² Reproductive migration can cover distances of greater than 1000 km,¹⁴³ but in general, they migrate for 450 to 500 km (Figure 6).¹⁴⁴ The return migration after spawning is more irregular, and can include moving into the floodplains to feed and recover the energy spent during reproduction. This is one of the species of Brazilian migratory fish that is able to ascend fish ladders and other fish pass facilities quite readily.¹⁴⁵

Other published information on this species include pesticide contamination;¹⁴⁶ genetics;¹⁴⁷ semen preservation and spermatogenesis;¹⁴⁸

¹³⁷ Bowen et al., 1984

¹³⁸ Sverlij et al., 1993; Fugi et al., 1996

¹³⁹ Bayo & Yuan, 1996

¹⁴⁰ Agostinho et al., 1993a

¹⁴¹ Gomes & Agostinho, 1997; Agostinho & Julio Jr, 1999

¹⁴² Godoy, 1957, 1975; Bonetto & Pignalberi, 1964; Bonetto et al., 1971; Bayley, 1973; Roldan & Canon Veron, 1980; Bonetto et al., 1981; Bonetto & Castello, 1985; Delfino & Baigún, 1985; Petrere Jr., 1985; Quirós & Cuch, 1989; Espinach-Ros et al., 1990; Agostinho et al., 1993a, 1994a

¹⁴³ Godoy, 1975; Espinach-Ros et al., 1990

¹⁴⁴ Agostinho et al., 1993a; Sverlij et al., 1993

¹⁴⁵ Quirós, 1988; Borghetti et al., 1994

¹⁴⁶ Matsushita & Souza, 1994; Moraes et al., 1997a; Ranzani-Paiva et al., 1997; Rodríguez et al., 1997; Mazon et al., 1999; Fernandes et al., 2000, Colombo et al., 2000

¹⁴⁷ Pauls & Bertollo, 1983; Verani et al., 1990; Revaldaves et al., 1997; Dias et al., 1998; Cavallaro & Bertollo, 2000

¹⁴⁸ Coser et al., 1984

morphology;¹⁴⁹ respiratory metabolism;¹⁵⁰ and parasitology.¹⁵¹ However, most of the publications are related to cultivation in hatcheries.¹⁵²

Pseudoplatystoma corruscans

P. corruscans, known in Brazil as the pintado or surubim, is the largest catfish in the Paraná Basin, with individuals up to 152 cm in length (slightly smaller than the maximum size encountered on the São Francisco River¹⁵³), but with only females exceeding 130 cm in length.¹⁵⁴ The fish occurs in moderate abundance in the sport and artisanal fisheries in the dams-free stretches of the Paraná Basin, but can enter the riverine zone of reservoirs to feed. The species is very popular in the marketplace, particularly for restaurants, and is among the ten most captured species in the Itaipu Reservoir.

The pintado is a nocturnal piscivore in all habitats, sizes or seasons.¹⁵⁵ Juveniles and adults are most abundant in marginal lagoons and meandering rivers, but only adults are found in the main channel of the Paraná River.¹⁵⁶ The examination of 481 stomach contents revealed the presence of 38 other fish species, invertebrates and the occasional other small vertebrate.¹⁵⁷ Experimental studies on gastric evacuation demonstrated that it takes 7.6 to 14.6 hours to complete the evacuation, depending on temperature.¹⁵⁸ The fish stops feeding when temperature drops below 18^oC. Growth curve parameters have been calculated.¹⁵⁹

P. corruscans spawns in running and shallow waters, from November to February, when the ovaries represent about 6% of the body weight. The number of oocytes can be up to 2.5 million per individual,¹⁶⁰ each

¹⁴⁹ Leite et al., 1988; Rizzo et al., 1998; Nachi et al., 1998; Blasquaz et al., 1990; Barbieri et al., 1989; Moraes et al., 1997b

¹⁵⁰ Fernandes et al., 1995; Barrionuevo & Fernandes, 1998; Severi et al., 1998

¹⁵¹ Ranzani-Paiva et al., 1995, 2000

¹⁵² Castagnolli & Cyrino, 1981; Rocha et al., 1989; Pinto et al., 1989; Verani et al., 1989; Castellani et al., 1994; Tamelli et al., 1994; Kawamoto et al., 1996; Cestarolli et al., 1997; Rizzo et al., 1997; Nuñer & Verani, 1998; Furuya et al., 1999; Galdioli et al., 2000; Portella et al., 2000a, 2000b

¹⁵³ Godinho et al., 1997; Sato et al., 1997

¹⁵⁴ Godinho et al., 1997

¹⁵⁵ Marques, 1993

¹⁵⁶ Agostinho & Julio Jr, 1999

¹⁵⁷ Marques, 1993

¹⁵⁸ Marques et al., 1992

¹⁵⁹ Palmeira, 1990; Mateus & Petrere, in press

¹⁶⁰ Sato et al., 1997

with diameter of about 0.9 mm. Sexual maturity is reached at 67 cm.¹⁶¹ The migratory behaviour of this species has been reported on by several researchers.¹⁶²

Other published studies on this species are on parasitology and pathology;¹⁶³ contamination by pesticides;¹⁶⁴ cytology, histology and embryology;¹⁶⁵ genetics;¹⁶⁶ and cultivation.¹⁶⁷

Pterodoras granulosus

P. granulosus is an armoured catfish known in Brazil as the armado or abotoado due to a row of bony plates along each side and a large and robust dorsal spine. This is the principal species captured by the artisanal fishery in the Itaipu Reservoir. Originally from the middle and lower parts of the basin, it colonized the upper stretches of the Paraná after the Itaipu Reservoir inundated Sete Quedas Falls, a natural barrier to distribution upstream. The current northern limit to the distribution of this species is a stretch impounded before 1982 (Jupiá Dam in the Paraná River). In the floodplain, it can be found in all types of environment, except creeks. It is most abundant in the riverine zone of the Itaipu Reservoir and in meandering rivers.¹⁶⁸ The maximum size recorded for P. granulosus in the Upper Paraná River was 69.6 cm and the first maturation of females is reached at 36 cm.

The armado is omnivorous, feeding on plants (fruits, seeds, and leaves), filamentous algae, molluscs, crustaceans, insects and small fish.¹⁶⁹ In the riverine zone of the Itaipu Reservoir, juveniles are concentrated in the transitional zone between the tributary and the reservoir, whereas adults are more frequent in the main body of the reservoir. In this area, the juveniles feed primarily on filamentous algae and microcrustaceans,

¹⁶¹ Suzuki, 1992

¹⁶² Cordiviola, 1966; Bayley, 1973; Lowe-McConnell, 1986.

¹⁶³ Pavanelli & Rego, 1992; Moravec et al., 1993a, 1993b; Machado et al., 1994, 1995, 1996; Moravec et al.,1994; Petter, 1995b; Kritsky & Boeger, 1998; Rall et al., 1998

¹⁶⁴ Matsushita & Souza, 1994; Moraes et al., 1997a; Hylander et al., 2000

¹⁶⁵ Satake et al., 1994, 1995; Cardoso et al., 1995; Soares et al., 1995, 1996; Bazzoli & Godinho, 1997; Rizzo et al., 1998

¹⁶⁶ Souza et al.,1997

¹⁶⁷ Freire Filho et al., 1997; Miranda & Ribeiro, 1997; Ribeiro & Miranda, 1997; Rizzo & Bazzoli, 1997; Sato et al., 1997; Giovane et al., 1999; Tavares et al., 2000

¹⁶⁸ Agostinho & Julio Jr, 1999

¹⁶⁹ Hahn et al., 1992, 1997

whereas adults feed mostly on plants and molluscs.¹⁷⁰ The analysis of stomach contents from individuals caught in the floodplain upstream of the Itaipu Reservoir showed a large incidence of seeds, especially during the rainy season. Twenty seven plant genuses were identified in the diet, dominated by plants of the Moraceae family and with Ficus, Cecropia and Polygonum the most abundant. The quantity of intact and viable seeds in the final portion of the gut suggests that this fish can be important for the dispersion of plant species¹⁷¹ such as Cecropia pachystachya.¹⁷²

The armado uses the area upstream of the Itaipu Reservoir, and probably the large lateral tributaries, to reproduce. The best records of individuals spawning are from a meandering tributary, the Iguatemi River. Spawning occurs repeatedly during the spawning season, which occurs later than that of other migratory species (January to March). During this period, ovaries constitute 6.6% of the body weight and contain about 724,000 oocytes per individual,¹⁷³ each with a diameter of about 1.1 mm.¹⁷⁴

Tagging experiments with P. granulosus revealed that upstream movements occur from October to January, while downstream movement occurs from January to March.¹⁷⁵ Individuals of this species caught and tagged downstream of the Itaipu Dam and released into the reservoir were recaptured 180 km above the reservoir, demonstrating their ability to continue migration through a still water body. Bonetto et al. (1981) recorded displacement of up to 1000 km for this species.

Other published studies about the species are on parasitology¹⁷⁶ and hematology.¹⁷⁷

Rhaphiodon vulpinus

R. vulpinus, a distinctive long-bodied and laterally compressed characid known in Brazil as the dourado-cachorro, peixe-cachorro or facão due to two large and prominent canine teeth. It inhabits open waters, and is currently an abundant fish in the Paraná Basin in both running water

¹⁷⁰ Agostinho & Julio Jr, 1999

¹⁷¹ Stevaux et al., 1994

¹⁷² Pilati et al., 1999

¹⁷³ Gosso & Iwaszkiw, 1993

¹⁷⁴ Suzuki, 1992

¹⁷⁵ Agostinho et al., 1994a

¹⁷⁶ Thatcher, 1981; Lopes et al., 1991; Hoineff et al., 1992; Pavanelli et al., 1994; Petenusci et al., 1996; Moravec & Thatcher, 1997

¹⁷⁷ Satake et al., 1991

and reservoirs located in or close to the Paraná River.¹⁷⁸ In the Itaipu Reservoir, the fish is most abundant in the top 5 m of water and is important in the landings of the artisanal fisheries.¹⁷⁹ This species grows up to 71.8 cm in length with first maturation occurring at 40 cm. Growth curve parameters were estimated by Perez-Lizama (1994).

The dourado-cachorro is piscivorous, feeding primarily in running water at night, and generally hunting in shoals close to the bank where they capture small characins. Invertebrates are a secondary food item found in the stomach of juveniles.¹⁸⁰

Spawning occurs in running waters, from October to January, when the ovaries represent more than 15% of the body weight,¹⁸¹ and contain around 348,500 oocytes,¹⁸² with diameters of 1.1 mm.¹⁸³

Little other information is available about the biology and ecology of R. vulpinus, other than studies on parasitology¹⁸⁴ and morphology.¹⁸⁵

Rhinelepis aspera

R. aspera, known as cascudo preto in Brazil, is another armoured catfish. At one time, this fish was widely distributed in the Paraná River Basin, living on rocky bottom in running waters. Many regional stocks were recognized, but most of these now appear to be extinct.¹⁸⁶ In 1959, the cascudo preto was the most important species in the fisheries of the Piracicaba River, contributing 50% of the landings.¹⁸⁷ In the 1980s it was also a prominent part of the fisheries in the Paranapanema River.¹⁸⁸ It is now absent in the commercial catches of both of these rivers, probably due to pollution, impoundments and overfishing.

In the case of the Itaipu Reservoir, this species historically supported an important fishery in the river immediately above the reservoir. In 1984, some daily catches approached a metric ton. From 1987 to 1991, R. aspera

¹⁷⁸ CESP, 1993; Agostinho & Julio Jr, 1999; Santos & Formagio, 2000

¹⁷⁹ Fuem.Nupélia/Itaipu Binacional, 1998

¹⁸⁰ Almeida et al., 1997; Hahn et al., 1997

¹⁸¹ Suzuki, 1992

¹⁸² Iglesias & Schubart, 1999

¹⁸³ Suzuki, 1992

¹⁸⁴ Moravec et al., 1993a, 1993b

¹⁸⁵ Nelson, 1949

¹⁸⁶ Agostinho et al., 1995b

¹⁸⁷ Monteiro, 1963, 1965

¹⁸⁸ Agostinho & Barbieri, 1987a, 1987b

was among the five most important species in the landings, averaging an annual catch of 64 metric tons. However, since 1991 the fisheries of this species has been declining, showing signs of overfishing.¹⁸⁹

The cascudo grows up to 54 cm in length, and reaches its first maturation at a size of 25 cm. Growth curve parameters were estimated by Agostinho et al. (1991). The fish is iliophagous, feeding on finely grained detritus. It takes food in by suction, and possesses adaptations such as a respiratory membrane and well developed branchial rack¹⁹⁰, rudimentary labial and pharyngeal teeth, thin stomach wall, and very long intestine to deal with this feeding habit.¹⁹¹

Spawning occurs from October to January after long migrations in running water. Ripe ovaries represent up to 15% of the body weight, and contain up to 180,000 oocytes, with diameters of 1.3 mm.¹⁹² Suzuki et al. (2000) compared oocyte morphology and reproductive strategies of five species of loricarid catfish and concluded that the cascudo preto differs considerably from the others with its reproductive migration, a curtailed spawning period, high fecundity, small eggs and broadcast spawning with no parental care.

Gill morphology and respiration of the cascudo preto have been extensively studied¹⁹³. Other published studies addressed parasitology,¹⁹⁴ gonad histology,¹⁹⁵ cultivation¹⁹⁶ and systematics.¹⁹⁷

Salminus hilarii

S. hilarii, known in Brazil as the tabarana, is a migratory characid smaller than its better known congeneric dourado (S. maxillosus), with reported maximum sizes of 42 cm for females and 30 cm for males.¹⁹⁸ This species inhabits main tributaries of the Paraná River, and is extremely rare in the main channel of this river. The preference for small water bodies makes

¹⁸⁹ Agostinho et al., 1995b

¹⁹⁰ Castro et al., 1999

¹⁹¹ Delariva & Agostinho, 2001

¹⁹² Agostinho et al., 1991

¹⁹³ Santos et al., 1994; Perna et al., 1995; Perna & Fernandes, 1996; Armbruster, 1998a, 1998b; Takasusuki et al. 1998; Panepucci et al., 2000

¹⁹⁴ Ribeiro et al., 1989; Eiras et al., 1990; Moravec et al., 1992; Petter, 1994

¹⁹⁵ Agostinho & Barbieri, 1987a, 1987b

¹⁹⁶ Sato et al., 1998; Soares et al., 1998

¹⁹⁷ Armbruster, 1998a, 1998b

¹⁹⁸ Godoy, 1975

this species more susceptible than the dourado to local extinctions from pollution and impoundments.

The tabarana is a piscivore as an adult,¹⁹⁹ whereas fry feed on zooplankton and juveniles eat insects tending towards piscivory as they grow. Spawning occurs from November to January, with mature ovaries representing up to 15% of the body weight and 30,000²⁰⁰ to 52,000²⁰¹ oocytes per individual. Magalhães (1931) reported that reproductive migration begins when the rainy season starts, ascending the upper stretches of the tributaries and concentrating to spawn in areas where the water is clean and shallow (<1.0 m deep).

Just one recent publication was found about this species, and this refers to parasitology.²⁰²

Salminus maxillosus

S. maxillosus, known in Brazil as the dourado, is the largest characin of the Paraná Basin. Once common, it is now only caught sporadically in rivers such as the Paranaíba, Grande, Tietê and Paranapanema. In the dams-free stretches of the basin it has moderate abundance compared with other migratory species, and is targeted by artisanal and sport fisheries, particularly by weekend anglers. The species is the most valuable sport fish in these sections of the river, exemplified by a large annual international tournament in the first kilometers of the river below the Itaipu Dam. The maximum total length recorded in this area was 92 cm, but fish up to 116 cm have been reported.²⁰³ Males are smaller than females, with a maximum length of 75 cm. Maturity in females is reached at 51 cm. Ageing and growth were studied by Sverlij and Espinach-Ros (1986).

The migratory behaviour of this species is conspicuous and has been mentioned by many authors.²⁰⁴ Petrere Jr. (1985) reviewed the migration information for this and other species. S. maxillosus can migrate up to 1000 km at up to 21 km/day to reach spawning sites in the upper stretches of tributaries of the Paraná River. However, in an 80 km lotic stretch of the Paranapanema River, between Capivara and Salto Grande reservoirs,

¹⁹⁹ Godoy, 1975

²⁰⁰ Godoy, 1975

²⁰¹ Nomura, 1973

²⁰² Kohn et al., 1997

²⁰³ Godoy, 1975

²⁰⁴ Bonetto & Pignalberi, 1964; Godoy, 1967, 1975; Bonetto et al., 1971; Bayley, 1973

schools of this species were still observed during the reproductive period, 15 years after the construction of these dams, without access to the upper tributaries. The Canoas Reservoir has now also impounded this last free stretch of the river.

Reproduction occurs from October to January, depending on the flood regime of the particular year. Ripe ovaries represent up to 16% of the body weight,²⁰⁵ and contain up to 2.6 millions oocytes²⁰⁶ with diameters of 1.4 mm.²⁰⁷ According to Godoy (1975), this fish spawns in running water after the water levels have begun to rise. As with other characins, the eggs drift to the lower parts of the tributaries while undergoing embryonic development and are washed into the floodplains and marginal lagoons where the larvae complete development and juveniles find food and shelter.

The adult dourado is a top piscivore of the aquatic food chain, feeding in fast running water primarily during the twilight period.²⁰⁸ Fry, on the other hand, may feed on zooplankton,²⁰⁹ though they are also piscivorous in culture.

Other published information on the species refers to parasitology,²¹⁰ contamination by pesticides,²¹¹ genetics,²¹² and cultivation techniques.²¹³

Steindachneridion spp.

Steindachneridion, also known as surubi in Brazil, is a genus of pimelodid catfishes that includes an unknown number of species. The most popular is S. scripta. Similar to S. hilarii, it inhabits tributaries of the Paraná River and is never caught in the main channel of this river. Like other pimelodids, it prefers deep water in mid-sized streams with rocky bottoms. Traditional knowledge suggests that species of this genus are naturally rare, however, it is the only large migratory fish in the Iguaçu River, an important tributary of the Paraná.

²⁰⁵ Vazzoler, 1996

²⁰⁶ Godoy, 1975

²⁰⁷ Suzuki, 1992

²⁰⁸ Hahn et al., 1997; Agostinho et al., 1997; Almeida et al., 1997

²⁰⁹ Godoy, 1975

²¹⁰ Boeger et al., 1995b; Petter, 1995a, 1995b; Pavanelli et al., 1995; Kohn et al., 1997; Molnar et al., 1998; Isaac et al., 2000

²¹¹ Matsushita & Souza, 1994

²¹² Margarido & Galetti Jr., 1999

²¹³ Coser et al., 1984; Amutio et al., 1986; Pelli et al., 1997

There is little published information on this genus. Unpublished data from the Iguaçu, Piquiri and Corumbá rivers (probably different species) show that the fish may grow up to 73 cm, is piscivorous, and spawns from December to February with oocytes of about 1.8 mm diameter. All the recent literature deals with taxonomy and systematics.²¹⁴

IMPACTS ON MIGRATORY SPECIES

Fisheries Impacts

As in other basins in South America, data on fisheries are scarce for the Upper Paraná and information that is available from different parts of the basin, especially from reservoirs, is scattered. Long-distance migratory fishes in the Upper Paraná include all the large species and some of the medium-sized fishes present. Because of their size and excellent flesh, they bring the best price in the market and are therefore the preferred catches of artisanal fisheries. Sport fisheries also target most of them, in particular the large piscivores.

Surveys in the Upper Paraná Basin have identified three types of fishery:

• Artisanal – by fishers who live in small towns along the river bank.
• Subsistence – undertaken by small farmers or day workers who live on islands or along the rivers and reservoirs.
• Recreational or sport – by inhabitants of major cities in the region.

These three fisheries have been characterised in both reservoirs²¹⁵ and rivers.²¹⁶

Artisanal fisheries

Reservoirs – Reservoirs dominate the landscape in the Upper Paraná Basin. In the artisanal fishery, fish are caught mainly with nets (gill and trammel nets), but long lines and cast nets may be used to catch some species. In the Itaipu Reservoir, over 60 species may be exploited, seven of

²¹⁴ Lundberg et al., 1991; Oliveira & Moraes Jr, 1997; Figueiredo & Carvalho, 1999a, 1999b

²¹⁵ Agostinho et al., 1994b; CESP, 1996; Okada et al., 1996

²¹⁶ Petrere & Agostinho, 1993

the ten most important being migratory species (Figure 9).²¹⁷ Among the four most important species in the reservoir (accounting for more than 75% of the 1,560 tons landed annually), two are migratory: P. lineatus (caught with gillnets) and P. granulosus (caught with long lines), and make up 14% and 16%, respectively, of the catch.²¹⁸ P. lineatus was initially the most abundant in the fisheries when the reservoir first formed, but has now decreased and has been replaced by P. granulosus as the lead fishery. Migratory fish are caught primarily in the fluvial and transitional zones of the reservoir, ²¹⁹ being virtually absent from the lacustrine zone.²²⁰ Other than P. granulosus and P. pirinampu, the numbers of large migratory fish in the reservoir is decreasing, as indicated by a decreasing CPUE.

The maximum sustainable yield for all species from the Itaipu Reservoir has been estimated at 1,600 tons, with an optimum fishing effort of 96,000 fisher-days.²²¹ In 1993, fishing effort was 120,817 fisher-days (exceeding the optimum) with a catch of 1,500 tons, suggesting possible overfishing. Growth overfishing was identified for stocks of some migratory species (P. granulosus, P. luetkeni, P. corruscans) and recruitment and growth overfishing were identified for the stock of R. aspera, whose catches declined by 70% and in which only small individuals were landed by the end of the period.²²²

In spite of the high fishing effort, yield in reservoirs of the Upper Paraná Basin is low compared with other parts of the world. Estimates since 1986 indicated annual commercial yield averaged about 9 kg/ha. In contrast, commercial fishery yield averaged 152 kg/ha in reservoirs of northeastern Brazil²²³, 88 kg/ha in African lakes and reservoirs²²⁴, and 13 kg/ha in recreational fisheries in reservoirs in the USA.²²⁵ Possible reasons for the low yield include low primary production, absence of lacustrine-adapted species, long food chains, high numbers of piscivorous species, and fishing effort and gear restrictions. Low hydraulic retention time of the reservoirs probably interacts with precipitation patterns to

²¹⁷ Agostinho et al., 1995a; Okada et al., 1996

²¹⁸ Agostinho et al., 1999b; Miranda et al., 2000

²¹⁹ Thornton et al., 1990

²²⁰ Agostinho et al., 1999a

²²¹ Okada et al., 1996

²²² Okada et al., 1996

²²³ Paiva et al., 1994

²²⁴ Marshal, 1984

²²⁵ Miranda et al., 2000

FIGURE 9. Annual catches of large migratory species in the artisanal fisheries of the Itaipu Reservoir as total yield (bar graph) and CPUE (line graph)

curtail primary production.²²⁶ Fishery nonetheless remains important for the region because it is the sole protein source for local people, and because wages earned for most local jobs are inadequate for supporting a family.²²⁷

Surveys in seven reservoirs in the basin showed that migratory species are important components of the landings (Figure 10).²²⁸ Reservoirs with greater fishery yields (around 11 kg/ha) are those with upstream stretches without dams (Itaipu and Barra Bonita reservoirs) or large lateral tributaries (Jupiá Reservoir). For large migratory species such as P. lineatus, P. maculatus and P. granulosus, the existence of free stretches upstream or large lateral tributaries are essential. Among these species, the most important for the artisanal fishery in all reservoirs is curimbatá (P. lineatus). Its contributions to the total catch varied according to reservoirs, from 12% (5 tons/yr) in Ibitinga Reservoir to 37% (61 tons/ yr) in Jupiá Reservoir. In the Itaipu Reservoir, where fishing is more intense, this species makes up 14% of the catch (224 tons/yr).

Rivers – Information on lotic fisheries in the Upper Paraná is sparse. Preliminary surveys indicate that artisanal fisheries in rivers differ from

FIGURE 10. Yield of large migratory fishes from reservoirs of the Upper Paraná River Basin²²⁹

²²⁶ Fernando & Holcik, 1982; Paiva et al., 1994; Agostinho & Zalewski, 1995; Petrere, 1996; Gomes, 1999; Agostinho et al., 1999a

²²⁷ Agostinho, 1994b; Agostinho et al., 1999b

²²⁸ Torloni et al., 1993; Petrere & Agostinho, 1993; Agostinho et al., 1995a, CESP, 1996

²²⁹ CESP, 1996; Agostinho et al., 1994a

those in reservoirs. Fishers target large catfishes (pimelodids, such as P. corruscans), a characid (S. maxillosus), anostomids (L. elongatus and L. obtusidens) and a prochilodontid (P. lineatus).

After the closure of the Itaipu Dam and dispersion upriver, P. granulosus (an armoured catfish) started to appear in the landings of the commercial fisheries. Four thousand eight hundred individuals of P. corruscans, totalling 24 tons, were taken and measured over one year (1987–1988) in the artisanal fishery of the Upper Paraná close to the town of Porto Rico, and it was concluded that this species seemed to be fairly abundant.²³⁰ P. corruscans and S. maxillosus are caught with hooks baited with live fishes (Gymnotus carapo, Hoplosternum littorale and young P. lineatus may be used as bait). In fishing for P. corruscans, the most preferred species, fishers set their branch hooks late at night to avoid attacks on the bait by piranha (Serrasalmus marginatus and S. spilopleura). Fishers also follow the movements of P. corruscans schools, sometimes for more than 100 km.²³¹ S. maxillosus and P. luetkeni are also caught with hooks (long lines and hand lines), but these fisheries are usually performed during daylight in the Paraná channel where piranhas are less abundant.

P. lineatus and P. granulosus are caught with gillnets, and P. granulosus is also caught with long lines baited with fruit. During their migration upriver to reproduce, beach seining around sandbanks is used to catch P. lineatus and R. aspera. As winter progresses and catches per unit effort decrease, the fishers work floodplain lakes and secondary channels.²³² Absence of data allows no inferences on yields.

The stocks of some migratory fish depend on the integrity of the flood pulse. In studies of the influence of flooding on P. lineatus on the Itaipu Reservoir fishery, it was concluded that low water levels, persisting for a relatively long period (as observed in 1986–1987), might be responsible for the total absence of young-of-the-year, and thus failing recruitment.²³³ This seemed to be the case for P. lineatus, whose stock decreased dramatically in commercial catches of the Itaipu Reservoir within a single year. In the year leading up to and including 1987 this species was the

²³⁰ Marques, 1993; Petrere & Agostinho 1993

²³¹ Buck, 1988; Petrere & Agostinho, 1993

²³² Petrere & Agostinho, 1993

²³³ Gomes & Agostinho, 1997

most important catch of the reservoir,²³⁴ contributing about 500 tons, but in the next and following years it contributed only about 220 tons annually.

Fish are usually marketed at both local and regional levels. Most of the fishers are linked to middlemen that buy the catch. Data from the commercial fishery in the Itaipu Reservoir indicate that the middlemen pay low prices for the harvested fish and sell them for at least double the price, enjoying most of the profits.²³⁵ Some of the catch goes to supermarkets in big cities in the region and some to neighbouring states such as São Paulo.

Subsistence fisheries

Virtually all islanders and a considerable part of the riverine population fish for subsistence, as fish are their main protein source. Islanders employ basic gillnets and to a lesser extent hook and line or poles, to catch medium-sized species, including some migratory species such as S. maxillosus, P. corruscans, P. mesopotamicus, L. obtusidens, L. elongatus, and P. granulosus.

Sport fisheries

The sport fishery along rivers occurs primarily during the weekend throughout the year. The river anglers target mainly S. maxillosus, B. orbignyanus, P. mesopotamicus, L. elongatus, L. obtusidens, P. corruscans, and P. luetkeni, and are restricted to the main channel and major tributaries. Techniques used are hook and line (poles), baited with live fish for catching S. maxillosus and P. corruscans, pieces of fish for P. luetkeni, seasonal fruit for P. mesopotamicus, and worms for the remaining species. Some tournaments are held in cities along the river bank, especially to catch L. elongatus. There is no information on their yields. The sport fishery in reservoirs is practised on small and medium sized sedentary fish by fishers from local and neighbouring cities.

²³⁴ Agostinho et al., 1994b

²³⁵ Agostinho et al., 1999b

Other Impacts

Genetic effects

There is some uncertainty about the impact of impoundments and fish stocking on the genetic diversity of migratory fish populations in the Upper Paraná. Few studies have characterised the population or analysed possible effects. Over the last four decades more than 26 large reservoirs have been constructed in the basin and 25 species have been stocked, including migratory species (P. lineatus, S. maxillosus, Leporinus spp.), hybrids (P. mesopotamicus x Colossoma macropomum) and exotic species (Plagioscion squamosissimus, Triportheus angulatus, Hoplias lacerdae, Astronotus ocellatus, Oreochromis niloticus).

After depletion of large migratory fish stocks in the higher reaches of the Upper Paraná Basin, especially in bigger tributaries such as the Tietê, Grande and Paranapanema, attention has been devoted to the possible loss of genetic variability. The loss could be a result of population fragmentation, loss of spawning sites, and especially the genetic quality of the hatchery fry used in stocking. In the stretch of the Upper Paraná free from dams, electrophoretic analysis of 19 enzymatic systems of P. lineatus from the Paraná and two tributaries (Ivinheima and Baia rivers) revealed that the three sub-populations share a high degree of heterozygosity and polymorphism.²³⁶ The values for the Nei statistic,²³⁷ used to estimate the degree of genetic similarity among populations, were high.²³⁸ This suggests that these populations are a single stock, indicating their appropriateness for use as parental stock for the basin. However, the material analyzed in that study was collected from a short stretch of the Paraná Basin unaffected by dams. The authors of the study are currently developing a project to investigate the effects of damming on the genetic variability of P. lineatus in the Plata Basin. The aim is to examine the usefulness of RAPD in P. lineatus as a source of genetic markers to quantify genetic variability of the sub-populations that will be collected in some locations of the two most important rivers in the Plata Basin: the heavily dammed Paraná, and the Paraguay River, which has not been dammed.

²³⁶ Revaldaves et al., 1997

²³⁷ Nei, 1978

²³⁸ Paraná x Ivinheima = 0.999; Baia x Ivinheima = 0.999; Paraná x Baia = 0.996

Negative impacts of dams

Electricity plants in Brazil generate 78,000 MW annually. Presently 90% of the energy consumed in the country comes from hydroelectric power, of which dams in the Upper Paraná and other small basins in southeast Brazil generate more than 70%.²³⁹ The main impacts on migratory fishes in the Upper Paraná are therefore a result of dam construction.

The series of dams in the main tributaries of the Upper Paraná has been blamed for the virtual absence of large migratory fish in the basin.²⁴⁰ Abundant before the impoundments,²⁴¹ these species were important in artisanal fisheries along the upper tributaries of the Paraná.²⁴² Today, S. maxillosus, P. luetkeni, P. corruscans, B. orbignyanus, and P. mesopotamicus are caught only sporadically in rivers such as the Paranaíba, Grande, Tietê, and Paranapanema. However, P. lineatus and Pimelodus maculatus still make a reasonable contribution to the bulk of the catches in reservoirs, that have large tributaries or upstream stretches without a dam, where they may reproduce. Short-distance migrators such as Hypophthalmus edentatus, A. bimaculatus and P. squamosissimus (Figure 3) can also inhabit a reservoir, reproducing in lateral tributaries, upstream stretches or even the fluvial zone of the reservoir.²⁴³

Migratory neotropical species generally range widely, with spawning sites and growth areas up to 1000 km or more apart.²⁴⁴ For the early life stages the species also require nurseries, which are lentic and more vegetated, usually between spawning sites and adult habitats. The most conspicuous impact dams have on migratory fish in the Upper Paraná is the separation of spawning grounds from nurseries and feeding sites. The intensity of impacts from damming will thus depend on the dam site in relation to the three types of habitats required by migratory species. Adults of migratory species may inhabit fluvial parts of reservoirs, and spawn when long stretches of unimpounded river exist upstream. However, the lentic conditions in the main parts of a reservoir are unfavourable to migratory fishes.

²³⁹ Petrere et al., 2002

²⁴⁰ Agostinho et al., 1999a

²⁴¹ Godoy, 1975

²⁴² Monteiro, 1963

²⁴³ Agostinho et al., 1995a, 1999a

²⁴⁴ Godoy, 1957; Bonetto, 1963; Petrere, 1985; Agostinho et al., 1994a

Besides blocking migratory routes, dams also alter the flood regime. Above the dam, the floodplain is permanently inundated by the reservoir. Below the dam, floods are reduced and time lags are introduced into the peaks (Figure 11). As a result, the area seasonally inundated is reduced, or is flooded at the wrong time, altering the connectivity between the river and important nursery habitats and interfering with the stimuli that lead to spawning.

Positive impact of dams

The succession of reservoirs in the Upper Paraná tributaries appear to serve as settling chambers that improve the water quality. Thus, the intense pollution in the headwaters of the Tietê River from São Paulo City and from industries results in very poor water quality in the initial reservoirs, but is no longer detectable six reservoirs downstream where the river enters the Paraná.²⁴⁵ These tendencies improve the quality of fish for human consumption, but decrease productivity due to the sedimentation of nutrients. Despite the virtual absence of large migrants in these reservoirs, production of fish biomass is greater than in the rivers, and intense artisanal and recreational fisheries are present.

Agriculture and ginseng extraction

Intense agriculture and cattle-raising (mostly with inadequate soil management), the heavy use of agricultural chemical agents and the

FIGURE 11. Natural and regulated discharges of the Paraná River upstream of the Itaipu Reservoir²⁴⁶

²⁴⁵ Barbosa et al., 1999

²⁴⁶ Agostinho & Zalewski, 1995

elimination of riparian vegetation have degraded water quality in the chief tributaries of the Upper Paraná, the spawning grounds for migratory fishes. In the stretch of the Upper Paraná that is not dammed, the environment is still altered significantly by changing water levels induced by upstream dams and by cattle-raising, irrigated rice culture, extraction of Pfaffia (Brazilian ginseng, a tuber used in the cosmetic industry), mining (sand extraction) and navigation.

Cattle enter the islands mainly during low water periods when landowners have difficulties keeping the cattle on their own pastures. Trampling compacts the soil, erodes the borders of the islands and destroys emerging vegetation, which can be important during the formation of temporary lagoons. Deforestation and fire (intended to favour growth of herbaceous vegetation) both worsen the situation. To find the Pfaffia shrub (the first species to emerge out of charred ground), extractors burn the riparian vegetation, an important food source for P. mesopotamicus. Rice culture in flooded areas involves draining and sometimes the use of chemical agents. Absorbing the varzeas (flooded forests) into agricultural production in these ways eliminates an important nursery area for migratory fishes.

Mining and navigation

Although limited to the main channel of the Paraná, mining by nearly 30 companies has a significant impact on riparian vegetation and river channel habitats. Navigation projects for the Upper Paraná bring heavy traffic of medium-sized and big boats that ship agricultural products from the western and eastern regions of the states of Paraná and Mato Grosso do Sul, respectively, to the port of Santos in São Paulo State. These boats begin their trip in the Itaipu Reservoir, navigate along the free stretch of the Paraná, pass through locks of the Paraná and the Tiête rivers, and dock in the latter. Pollution from the ships and erosion of the river banks by their wake are expected consequences with the potential to affect migratory fish.

MANAGEMENT AND MITIGATION

Legislation

The São Paulo State Law Number 2250, dated December 28, 1927, Article 16, mandated the installation of fish ladders on dams. This Law was so controversial at the time that a specialist from the US (J. H. Brunson) was consulted to analyse the need for fish ladders in Brazil. In 1929, he concluded that fish ladders more than 9 m high were not efficient. This conclusion was based on the US experience because there was no information available for Brazil.²⁴⁷ In 1934 a new Federal Law was promulgated,²⁴⁸ which stated that all dams producing electricity should have mechanisms to allow the preservation and movement of fish. In 1938 a new law²⁴⁹ stated that dams must have mechanisms that allow the preservation of ichthyofauna, either by the construction of fish ladders or by constructing hatcheries. As a result, and in light of Brunson’s conclusions on the inefficiency of fish ladders, the hydroelectric companies built several hatcheries. In 1967, Decree Law 221 (28/02/67) delegated to SUDEPE (Federal Agency for the Development of Fisheries) the task of determining the best mechanism for the protection of the aquatic fauna. This agency, whose main purpose was fish culture development, through Resolution 46 (27/01/71) made one hatchery mandatory in each sub-basin where dams were built.

Consideration of Environmental Impacts Studies dates from 1981.²⁵⁰ In 1983 it became mandatory to submit a Report of the Impacts on the Environment that would include a survey of the area, a description of the proposed action and alternatives, and identification, analysis and prediction of the major positive and negative impacts.

A new law²⁵¹ makes it a crime to kill, hunt, take or use wild fauna either native to the location or in migration, without official permission, licence or authorisation.

²⁴⁷ Alzuguir, 1994

²⁴⁸ Decree number 24,643; July 1934; Article 143, named Water Code

²⁴⁹ Decree Law number 794; October 19, 1938; Article 68

²⁵⁰ Law Number 6938; August 31, 1981

²⁵¹ Article 11 of Decree Law Number 3179, September 21, 1999

Legislation to reduce exploitation of long-distance migratory fish juveniles and to protect spawning grounds prohibits fisheries during the spawning season and restricts the mesh-size of nets and the number of hooks used by fishers. More restrictive regulations are published annually to control fisheries during spawning (piracema) in state border rivers (Federal Agency) and rivers within a given state (State Agencies). The legislation is enforced by a State Environmental Agency. However, these regulations are unsuccessful because of the absence of exploitation/ resource monitoring, because money and human resources are lacking, because there is no clear target for action, and because there is a shortage of information locally about the species.

In the unimpounded stretch in the Upper Paraná where migratory fish such as S. maxillosus, P. mesopotamicus and L. elongatus are valuable to the recreational fishery, the ban on fishing during spawning (November to February) is rarely enforced. No information exists on the number of illegal fishers or on how many fish are taken from the Upper Paraná during the ban. It is also not uncommon that in some years, when floods are delayed, the season reopens just when the fish are beginning to migrate or spawn.

In tributaries of the Upper Paraná, fisheries are regulated by different legislation. Artisanal fishing is not permitted in the Goiás and Mato Grosso do Sul states and is regulated in the Paraná, São Paulo and Minas Gerais states. Recreational fisheries however, are permitted in all of the states.

Fish Passages

The adequacy of fish passage facilities as mitigative tools in the Paraná is doubtful, particularly because the reproductive strategies of migratory fishes rely on passive drifting of eggs and larvae until adequate development habitats such as shallow marginal lagoons are entered. The reservoirs that lie between the spawning sites and the nursery lagoons are usually calm water, causing the eggs to stop and sink before they reach the lagoons; because the water of the reservoirs is relatively clear, the eggs are seen by small omnivorous fishes and eaten.²⁵² Studies of eggs and larvae

²⁵² Agostinho & Gomes, 1997

conducted by Nupélia/Universidade Estadual de Maringá in the first kilometer below the Itaipu Reservoir demonstrate that (i) the larvae registered originated from the reservoir, as demonstrated by the fact that they belonged to essentially two species (90% sardela and 8.5% curvina) that reproduce in this environment, with their adult and reproductive forms absent from the stretch below the dam, (ii) the rate of damaged larvae (mutilated and crushed) reached values greater than 30% of the total, suggesting high mortality, in as much as those fragmented were not kept back by the ichthyoplankton net and (iii) no large migrator larvae were recorded.²⁵³ Thus, although adult migratory fishes may successfully use the passages, only a small proportion of their eggs may hatch out as fry.

Fish ladders are the device most relied on to mitigate impacts from dam construction in the Upper Paraná. The first fish ladder in Brazil was built in 1911 at the Itaipava Dam²⁵⁴ and is 7 m high. In the 1920s, the second fish ladder (3 m high) was constructed at the Cachoeira das Emas Dam (on the Mogi Guaçu River, a tributary of the Paraná).²⁵⁵

Based on the US experience with salmonids, fish ladders became mandatory in Brazil in 1927.²⁵⁶ The legislation stated that in every dam constructed (river, stream, or creeks), a facility to allow migratory fish to pass upstream was mandatory. But no studies were carried out on the fish fauna or appropriate ladder design. As a result, a fish ladder was constructed just above a 70 m high waterfall,²⁵⁷ or in streams where no migratory fishes were registered.²⁵⁸ Nor was evaluation performed after construction of the fish ladders, with a few exceptions. A few studies reported the high efficiency of the ladder in Cachoeira das Emas,²⁵⁹ and it was reported that several fish species were able to reach the upper part of a 27 m high experimental fish ladder at Itaipu Dam.²⁶⁰ However, the 11 m high ladder constructed at Salto Morais Dam (Tijuco River) was ineffective.²⁶¹

²⁵³ Agostinho et al., 2002

²⁵⁴ Pardo River, a tributary of Paraná River

²⁵⁵ Godoy, 1985; Quirós, 1988

²⁵⁶ Law No 2250/SP, 28/12/1927

²⁵⁷ in Negro Stream, São Carlos, State of São Paulo

²⁵⁸ Charlier, 1957

²⁵⁹ Godoy, 1957, 1975

²⁶⁰ Borghetti et al., 1993; 1994

²⁶¹ Godinho et al., 1991

Between 1957 and 1980, 23 ladders were built in dams in northeast Brazil, and all were reported to give satisfactory results.²⁶² However, other than recent data from the experimental fish ladder at the Itaipu Dam, there is no data on the efficiency of fish ladders in the big reservoirs of the Upper Paraná Basin. A fish ladder and elevator under construction in Porto Primavera Dam will be the first such facility in a large reservoir in the Upper Paraná.

Godoy (1985) concluded that ladders of less than 16 m in height would allow species to swim upstream, although problems in the ladder design could lead to malfunction. Data obtained by the Department of Environment of Itaipu Binacional²⁶³ showed that a vertical slot experimental ladder at Itaipu Dam (27 m high; 155 m long; and velocity of 1.2 m/s) enabled 28 out of 68 species registered downstream of the dam to reach the top of the ladder. Among the migratory species (large and medium) abundant in the ladder were P. lineatus, P. maculatus, and L. elongatus. Other large species, such as P. corruscans and B. orbignyanus were observed sporadically. P. mesopotamicus and P. luetkeni, registered downstream, were not seen in the ladder. The authors suggest that these species could not get into the ladder because they were either too high along the spine (P. mesopotamicus) or too large (P. luetkeni).²⁶⁴ The drive to spawn was suggested as an explanation for the high number of species and individuals in the ladder, as many of the fish had mature gonads. However, later work found a great number of juveniles, suggesting other factors may also be involved.

All the information available in the literature reported only the efficiency and ability of fish to use a ladder to reach reservoirs. No literature evaluated the influence of the ascended fish on the stocks upstream and downstream. Another problem associated with fish ladders and discussed only recently in Brazil is the continuation of migration once fishes reach a reservoir, specifically because the current that fish may need to navigate is greatly reduced in the reservoir. Tagging at Itaipu Reservoir²⁶⁵ suggested that migrants caught downstream and released upstream were able to

²⁶² Godoy, 1985

²⁶³ Fernandez, 2000

²⁶⁴ Borghetti et al., 1994

²⁶⁵ Agostinho et al., 1993a

continue their journey.²⁶⁶ Marked P. lineatus and P. granulosus from downstream of Itaipu Dam, released into the reservoir, were recaptured 180 km above the reservoir. Movement of these fish within the reservoir was slower than that of fishes released directly into the river. However, the velocity of fishes caught downstream and released into the reservoir was greater than the velocity of fishes caught and released within the reservoir. Seven of the nine recaptured individuals with the greatest displacement had been caught downstream and released upstream.²⁶⁷

Fish Elevators

The elevator installed in Yacyretá Dam, in the Middle Paraná, seems to be working more satisfactorily than others in the river system.²⁶⁸ In 1995, the elevator moved 44% of the species registered in the tailrace (totalling 1,767,000 individuals and 252 tons). These results have led to recent installation of elevators in the Porto Primaveira Dam of São Paulo as well. The results of these installations are not yet known.

Stocking

Stocking with exotic and native fish has been the most conspicuous strategy used by hydropower companies over the last decades to mitigate impacts on migratory fish in the Upper Paraná. Several hatcheries were constructed, billions of fry were stocked in most of the reservoir, and large amounts of money and effort were expended to restore fisheries. Initially stocking was done with exotic non-migratory species, of which more than two-dozen species were introduced from the Amazon Basin or from other continents. Fifteen of them are recorded in rivers and reservoirs of the Upper Paraná. However, only four species (P. squamosissimus, Cichla monoculus, O. niloticus and Tilapia rendalli) are harvested in commercial quantities. P. squamosissimus is currently the principal species in most of the artisanal fisheries of the Upper Paraná. Since 1980, species native to the basin have been stocked, but monitoring is restricted to only a few reservoirs and started only late in the decade.

²⁶⁶ 7,855 marked and 315 recaptured

²⁶⁷ FUEM.Nupélia-Itaipu Binacional, 1990

²⁶⁸ Convenio SECY T, 1996

Some native migratory species have also been stocked, especially Leporinus spp., P. lineatus, B. orbignyanus and pimelodid species. Among the native migratory species P. lineatus was the most stocked, making up 81% (up to 46,000,000 fry) of the total (Table 3). Other large migratory species used in stocking programs, but less intensely, were P. mesopotamicus, L. obtusidens, S. maxillosus, P. luetkeni and R. aspera.

TABLE 3. Number of fry released by the Companhia Elétrica de São Paulo in reservoirs of the Upper Paraná River Basin, 1979–1995²⁶⁹

Absence of monitoring or difficulties in distinguishing between stocked and unstocked fish in the catches do not allow conclusions on stocking efficiency, but current artisanal fisheries in the reservoirs are based on species that are not stocked.²⁷⁰

Protected Areas

The importance of the last unimpounded stretch of the Upper Paraná to the maintenance of biodiversity, including the conservation of migratory fishes, was recently recognised by the federal and state governments through the creation of three conservation units: (i) Environmental Protection Area of the Island and Varzea of the Paraná (10,031 km²); (ii) Ilha Grande National Park, occupying the lower half of the Ilha Grande Island; and (iii) Ivinheima State Park, including the main nursery area at

²⁶⁹ CESP, 1996

²⁷⁰ Agostinho et al., 1999a

Mato Grosso do Sul State (700 km²). These conservation units have different levels of use restrictions. However, the effectiveness of this strategy is still unclear, and many problems still exist. Fire, cattle-raising and drainage are forbidden, but enforcement is poor. In addition, the effects of upstream dam operation are substantial but are not considered in the strategy.

RECOMMENDATIONS FOR CONSERVATION AND RESEARCH

The outlook for migratory fish in the Upper Paraná is worsening. A new government hydroelectric plan foresees several dams in the main tributaries that are not yet impounded.

The lotic segment of the Upper Paraná is the last remaining stretch with a viable population of migratory fishes in this river inside Brazilian territory. Studies show that the integrity of the Upper Paraná floodplain is fundamental for the maintenance of the present recruitment levels that sustain the basin fisheries, especially artisanal fisheries in the Itaipu Reservoir. These studies also show that many species present in the region are absent in stretches of the river further upstream due to impoundments and poor water quality.

The majority of the human activities in the area violate the present environmental legislation. Organisations created to protect the region are pressuring landowners to remove cattle from the varzeas and islands. Prohibition of Pfaffia extraction should also be promoted. State environmental secretaries are presently working with academic and non-governmental organisations to find solutions to provide a harmonious balance between regional development and floodplain integrity.

The maintenance of fish diversity in the last free stretch of the Paraná within Brazilian territory, particularly in regard to populations of the large migratory species, depends on the integrity of the floodplain. Maintaining this integrity needs to deal with the ongoing human occupation in the region and will rely on better management of dams upstream.²⁷¹ The newly created conservation districts in the floodplain are appropriate for improving the level of preservation of the migratory fish nurseries, but there is neither enough money nor personnel to manage the districts,

²⁷¹ Agostinho & Zalewski, 1996

which fail to take in the spawning areas in the upper parts of tributaries. The main problem in the region (flow regulation by dams) also cannot be controlled by the administration of conservation districts. The level of information on the biology and ecology of migratory fish is also poor.

Proposed Conservation Strategy

A conservation strategy for the area should consider:

• Developing a research program to identify ecological zones that would provide information for decisions on alternative uses, and to evaluate the impact of anthropogenic activities;
• Evaluating the conservation status and biological/ecological requirements of migratory fish stocks;
• Identifying the potential users of migratory fish resources (i.e. sport and artisanal fisheries), their social, economic and environmental aspirations and constraints;
• Evaluating gear selectivity and impacts on fish stocks;
• Developing hatchery production of migratory species for stocking purposes, and methods for monitoring the genetic quality of the brood and the success of stocking programs;
• Identifying minimum instream flow and flood duration needed to trigger spawning and assure viability of eggs and larvae of the migratory species;
• Creating basin committees composed of municipal governments, research institutions, governmental and non-governmental organisations related to the environment, and others responsible for the management of the area. The purpose of these committees would be to propose guidelines to control the uses and occupation of the basin, including new impoundments and the operation of those already constructed;
• Requesting from power companies a broad research program before decisions on the siting of future dams in unimpounded tributaries are made, including areas critical to migratory fish spawning; and
• Promoting the restoration of spawning areas in the upper parts of the tributaries, in particular the rehabilitation of the riparian vegetation that has been illegally stripped.

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Sato, Y., N. F. Verani, J. R. Verani, L. J. S. Vieira, and H. P. Godinho. 2000. Induced reproductive responses of the neotropical anostomid fish Leporinus elongatus Val. under captive breeding. Aquaculture Research, 31:189–193.

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Smolders, A. J. P., G. van der Velde, J. G. M. Roelofs, and M. A. G. Hiza. 2000. El Nino caused collapse of the sabalo fishery (Prochilodus lineatus, Pisces: Prochilodontidae) in a South American river. Naturwissenschaften, 87(1):30–32.

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Soares, T. R. S., I. S. Watanabe, and R. A. Lopes. 1996. Light and scanning electron microscopic study of the stomach mucous of catfish Pseudoplatystoma corrucans, Agassiz, 1829 (Pisces, Pimelodidae). Brazilian Journal of Morphological Sciences, 13(1):152–152.

Souza, A. B., C. G. Fonseca, L. P. Ribeiro, and L. E. L. Pinheiro. 1997. Análise cromossômica do surubim Pseudoplatystoma corruscans das bacias dos rios S. Francisco e Paraguai. In Surubim. IBAMA, Belo Horizonte, Minas Gerais, 57–68 p.

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Suzuki, H. I. 1992. Variações na Morfologia Ovariana e no Desenvolvimento do Folículo de Espécies de Peixes Teleósteos da Bacia do Rio Paraná, no Trecho entre a Foz do rio Paranapanema e a do Rio Iguaçu. Dissertação (Mestrado em Zoologia), Universidade Federal do Paraná, 140 p.

Suzuki, H. I. 1999. Estratégias reprodutivas de peixes relacionadas ao sucesso na colonização em dois reservatórios do rio Iguaçu, PR, Brazil. Tese (Doutorado em Ecologia e Recursos Naturais), Centro de Ciências Biológicas e da Saúde, Universidade Federal de São Carlos, 97 p.

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Swarça, A. C., L. G. Caetano, A. L. L. Vanzela, and A. L. Dias. In press. Heteromorphism of rDNA size in Pinirampus pirinampu (Pisces: Pimelodidae) detected by in situ hybridization. Genetics and Molecular Biology.

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3
MIGRATORY FISHES OF THE
Paraguay–Paraná Basin
Excluding the Upper Paraná Basin

Emiko Kawakami de Resende

Empresa Brasileira de Pesquisa Agropecuária (Embrapa)

Embrapa Pantanal

Corumbá, MS, Brazil

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TABLE OF CONTENTS CHAPTER 3

CHARACTERISTICS OF THE BASIN

Introduction

The Paraná-Paraguay Basin encompasses most of southeastern Brazil, Paraguay, eastern Bolivia, and northern Argentina. As such, together with the smaller Uruguay River, it drains most of the central part of the continent southward into the Rio de La Plata estuary on the east coast (Figure 1). In size, it covers 2,800,000 square kilometers, second only to the Amazon Basin in South America.

FIGURE 1. The Paraguay-Paraná River Basin, showing river sections and principal features discussed in text²⁷²

²⁷² Also see Chapter 2

The Brazilian highlands and adjacent plateaus of the center of the continent are drained to the south by the Paraguay and Parana rivers; the São Francisco drains these to the northeast and the Amazon to the north. These highlands were worn down to sea level during the Paleozoic Era but were then uplifted again to their present elevation as the Andes formed, variously stagnating water drainage in temporary saline lakes and seaways and changing directions and connectivity of river systems in the process.²⁷³ The present topography ranges from level plateaus to rolling hills and deeply cut valleys.

Most of the drainage system of the Paraná-Paraguay Basin is hot and humid throughout the year, but with rains during the wet season primarily from October to March. Fifty percent more rain falls in the highlands than on the plains (respectively 1200 mm and 800 mm per annum), leading to substantial seasonal floods²⁷⁴ that are important to the biology of the basin.

The Paraná River originates at the confluence of the Grande and Paranaíba rivers in southern Brazil, and then runs generally southwest for 3,998 km before draining into the Rio de La Plata estuary. Eastern tributaries in the upper part, such as the Tietê, Paranapanema, and Iguaçu rivers, originate in the coastal mountains a short distance from the Atlantic but drain inland to contribute to the Paraná system. In some cases, as with the Tietê, the headwaters are situated in some of the most densely populated areas of the continent, and the upper reaches of the Paraná are the areas most intensively developed for hydroelectric generation.

The Paraná River can be divided into upper, high, middle, and lower sections,²⁷⁵ each with distinctive geographic, social or biological characters. Of these, the Upper Paraná has historically been adequately separated from the rest of the basin by the falls of Sete Quedas to be recognized as a distinct ictiofaunistic “province”.²⁷⁶ This portion of the basin is also sufficiently distinct in terms of social character that it is treated separately in the previous chapter, whereas the remainder of the basin is discussed here.

The Paraguay River originates west of the Mato Grosso plain in south-central Brazil, at 298 m above sea level. It is the fifth longest river in South

²⁷³ Lundberg et al., 1998

²⁷⁴ Lima Barros Dolabella, 2000

²⁷⁵ Agostinho et al., 1995; Bonetto, 1998

²⁷⁶ Bonetto, 1998

America (2,550 km), and is the principal western tributary of the Paraná. Its basin spreads over more than 973,000 square kilometers, including large parts of Brazil, Paraguay, and Bolivia. Throughout the basin, elevations rarely exceed 200 meters above sea level. The river is accessible to ocean-going ships and is plied mainly by local steamers travelling between the capitals of Argentina and Paraguay.

The Paraguay River has also been described in four sections by some authors, with the Upper and High Paraguay together constituting an ictiofaunistic province distinct from the rest of the basin.²⁷⁷ However, the distinction of the subdivision of the two halves of the river are not as clear in the Paraguay as in the Paraná, so I have opted to use the more common terminology of simply the Upper and Lower Paraguay.

Upper Paraguay

Geography, geology and river profile

The basin of the Upper Paraguay lies in the west-central region of South America, with a catchment area of around 496,000 km². Most of the basin lies within Brazil (358,514 km²) with the remainder in Bolivia and Paraguay.

Two great geological regions can be found in this portion of the Paraguay Basin: the highlands and the Pantanal, corresponding to Bonetto’s (1998) “Upper” and “High” river sections. The Paraguay first becomes navigable (84 m wide, 6 m deep) about 240 km downstream from its source in Brazil, after its confluence with the Sepotuba River. Where the Jauru River joins it (another 30 km downstream), it enters the Mato Grosso Pantanal floodplain, skirting the Pantanal’s western edge over a sandy bed and flowing around many islands. Important tributaries in this section are the Cuiabá, Taquari and Miranda rivers. Shortly before reaching Paraguay the river is joined by the Apa River, which flows in from the east and marks the end of the Upper Paraguay.

In the highlands, dense evergreen forest galleries grow along stream banks, whereas the Pantanal is a vast seasonally flooded plain. The fluctuation in water level over the plains depends largely on waters from the Pantanal to the north, with flood peaks from May to August and low

²⁷⁷ Bonetto, 1998

water from December to January. Geologically this portion of the river remained isolated from the Paraná Basin, draining into an inland saltwater lake where the Pantanal now stands, until the Paraguay River found a channel into the Paraná during the Holocene. The fish fauna of the Upper Paraguay therefore differs slightly from that of the Lower Paraguay and Paraná.²⁷⁸

The Pantanal

The Pantanal is a vast, virtually level inland plain that is flooded a large part of the year, due to the very low slope (1–3 cm/km from north to south and 6–12 cm/km from east to west). The Pantanal covers almost 40,000 square miles or approximately 175,000 km²; with 80% in the Brazilian states of Mato Grosso do Sul and Mato Grosso and 20% in Bolivia and Paraguay (Figure 1). Geologically, the basin is a relatively new sedimentary basin, whose non-consolidated alluvial sediments were washed down from the highlands during the late Quaternary (12,000–13,000 years ago).²⁷⁹ They are markedly sandy, with restricted areas of clay and organic deposits. Vegetation of the region is predominantly savannah, with scattered small trees and much grass. Plant species from the Amazon and from the Atlantic rainforests can be found in the Pantanal, along with typical Chaco vegetation.²⁸⁰

Despite its sandy character, the Pantanal floodplain is one of the largest and most complex wetlands of the world. There are surface lakes, floodable depressions, anastomosed channels, small temporary ponds, and the rivers themselves.

During the rainy season, the rainwater that comes from the highlands slowly covers the plain from north to south and from west to east, along the Paraguay River and its tributaries. When it rains intensely in the highlands and the plain at the same time, the Pantanal lies under a great sheet of water that leaves only the cordilheiras (low hills) dry. Unlike the grasslands of Rio Grande do Sul, which have been largely converted into pastures and wheat fields, the Pantanal has been left largely untouched, though it is used as a natural grazing land during the dry season.

²⁷⁸ Lundberg et al., 1998; Britski et al., 1999

²⁷⁹ Ab’Saber, 1988

²⁸⁰ Lima Barros Dolabella, 2000

The regional names for the Pantanal rivers include corixo, a temporary or permanent water channel that has its own river bed; vazante, a temporary river without its own bed that generally connects one lake to another during the rainy season; baías, temporary or permanent lakes; and salinas, saline lakes generally found in the Pantanal of Nhecolandia.²⁸¹ The rivers meander markedly, and there are many oxbow lakes and, on the western side, five large lakes; Uberaba (10,841 hectares), Gaíva (7,887 ha), Mandioré (13,765 ha), Vermelha (2, 846 ha) and Jacadigo (4752 ha).²⁸²

The most important tributaries of the Paraguay in the Pantanal are the Jauru, Sepotuba, Cuiabá, São Lourenço, Itiquira, Taquari, Negro, Aquidauana, Miranda and Apa rivers. The confluence with the Apa River is the southern limit of the Pantanal and the start of the Lower Paraguay River.

Because of the trapping and holding capacity of its wetlands, the Pantanal acts as a large buffer that releases its water downstream slowly, supporting an abundant fish fauna and other animals that depend on the fish for survival. Based on the type of dominant soils, vegetation, flooding depth and flooding duration, at least eleven different regions in the Pantanal can be identified. One of the most beautiful is Nhecolandia, with its numerous lakes and abundant wild animals, including marsh deer, jabiru storks, capybaras and caymans. Fish, apart from their importance to humans, are also a food base for several of these species, including the cormorant, jabiru, wood storks, caymans and giant otters.

Social characteristics

When the Bandeirantes, the pioneer European explorers of Brazil, first reached the west-central region in the early 1700s, the Mato Grosso area was inhabited by Bororo Coroado, Bororo Cabaçal, Bororo Campanha, Paresi, Umutina and Guató Indians. Today, the indigenous population has been reduced to the Paresi, Umutina and Bororo Coroado groups, living in seven of the eight indigenous reservation areas. The indigenous population in Mato Grosso do Sul State is made up of groups of Guarani-Kaiowá, Guató, Kadiwéu and Terena. The Guató population is estimated at 700 people, approximately 400 Living in urban areas (Corumbá and

²⁸¹ Resende, 1998

²⁸² Resende, 1998

Cáceres) and the rest in the Guató Island Insua and in riverside regions along the Paraguay and São Lourenço rivers. The Kadiwéu reservation has an area of 538,536 hectares and is inhabited by 1500 natives of the Kadiwéu and Terena groups, who lease their lands to non-natives for agriculture and cattle rearing. The Terena indigenous group occupies 17,329 hectares distributed into seven areas. Their main cultivated crops are rice, beans, corn, cassava and cotton.²⁸³ In some areas along the Miranda River, it is not uncommon that they lease the river out for fishing.

Approximately two million people now live in the Brazilian Upper Paraguay Basin, mostly in the highlands in a few large centres such as Cuiabá, Várzea Grande and Rondonópolis of Mato Grosso State. This region was accessible only by the Paraguay-Paraná rivers until the mid- 1900s, and the isolated human populations developed mechanisms to adapt and survive that are still found in a few rural communities and on traditional cattle farms. Today, the population consists predominantly of immigrants or their descendants originating from all over Brazil.²⁸⁴ Based on demographic indicators, a human population of 3,450,000 is estimated for the year 2025 for this part of the Paraguay Basin. Most will live in the highland cities.

The population of the Pantanal is about 206,000 inhabitants, at an average density of 1.8 inhabitants per square kilometer, which contrasts with the overall Brazilian average of about 17 inhabitants/km². Settlement of the region has been largely dictated by the flood patterns, which make much of the region unsuitable for year-round occupation.²⁸⁵ The population of the Pantanal plain is largely found on an estimated 3,500 cattle ranches, which, since the cattle range freely on natural pastures, employ very few workers.

Ninety percent of municipalities in the area have a reliable supply of water. However, treatment of solid waste, sewage and residual water is critically inadequate. Most of the urban houses use septic tanks for wastewater. In other situations wastewater is released directly to rivers without any treatment. In most cases the solid wastes collected by public services are spread on open fields or in trenches.²⁸⁶

²⁸³ PCBAP, 1997

²⁸⁴ PCBAP, 1997

²⁸⁵ Lima Barros Dolabella, 2000

²⁸⁶ PCBAP, 1997

The main economic activities in the highlands are cultivation (primarily soybean and corn) and beef cattle ranching based on seeded pastures. Sugar cane is also of great economic importance for some municipalities in Mato Grosso. Gold and diamond mining are important in the northern regions.

In the Pantanal plain, the most important traditional economic activity is beef cattle rearing on natural pastures. Sport fishing has grown in the last ten years to become the second most important economic activity in the Pantanal, with 56,000 fishermen arriving each year in the South Pantanal. The number visiting the North Pantanal is unknown, but 65,000 are estimated for the whole of the Pantanal. Some cities, such as Corumbá, Miranda and Porto Murtinho, depend on sport fishing for their economic survival.²⁸⁷

Lower Paraguay

Geography, geology and river profile

The Lower Paraguay begins at the confluence with the Apa River (Figure 1). It runs along the northeastern border of Paraguay for approximately 200 km before crossing Paraguay from north to south (more than 320 km). Crossing Paraguay, the eastern bank is elevated, while a low plain known as the Chaco Boreal spreads out on the west. The floodplain of this section is very poorly studied. Meeting the Pilcomayo at Asuncion, the river forms the southwestern border of Paraguay with Argentina for 330 km south to Corrientes, where it drains into the Paraná. Authors that divide the Lower Paraguay into two sections²⁸⁸ do so with the division at Asunción.

From the Apa to the Paraná, the Paraguay flows on a broad, shallow bed, averaging about 600 m wide. In Argentina, where it broadens to 700 m, the banks are very low and floodwaters create a very large floodplain between 5 and 15 km wide. Similarly to the Lower Paraná, the climate changes from subtropical in the north to temperate in the south.

To the west of the Lower Paraguay and the Middle Paraná lies the Gran Chaco, an immense lowland plain. Composed of extremely deep unconsolidated sand and silt, nearly free of stones, the Gran Chaco is the

²⁸⁷ PCBAP, 1997

²⁸⁸ Bonetto, 1998

alluvial fill of a vast geosynclinal basin formed by downwarping or submergence of the area between the Andean Cordillera on the west and the Brazilian Shield on the east. It is largely uninhabited, arid and subtropical. Two main rivers, the Pilcomayo and Bermejo, cross its low forests and savannahs. Roads and rail lines are rare. The Gran Chaco covers about 730,000 square kilometers, of which slightly more than one-half lie inside Argentina, one-third in Paraguay, and the remainder in Bolivia.

No major obstacles have yet been built in this section of the river that alter water flow, and the major impacts recognized to date are due to agriculture and cattle rearing along the tributaries.²⁸⁹

The Bermejo and Pilcomayo rivers, which drain from the Andes foothills into the Gran Chaco, are typical of most rivers of the Chaco and are called “Chaco streams”. Their courses are marked by countless sloughs, oxbow lakes, braided channels, sandbars and vast swamplands; losses from flooding, seepage, and evaporation are so high that little of their full flow reaches the mouth. Most of the Chaco is so poorly drained that the very shallow and irregular channels lead to rapid and extensive flooding during the very rainy summers and Andean draining. At the peak of these floods, as much as 15% of the Chaco may be under water.²⁹⁰

Social characteristics

The upper portion of this part of the Paraguay Basin lies in Paraguay, the country with perhaps the most racially homogeneous population in South America. A large majority of the people are of mixed white (especially Spanish) and Guarani Native American descent. More than half live in rural areas. In the last census of 1993 the population was estimated at 5,070,856. The density is higher in the western region, on the left bank of the Paraguay River, and most sparse in the Chaco, on the right bank.

Farming is the principal industry of Paraguay. The main crops are cassava, sugar cane and soybean. Livestock breeding and forestry are other major occupations. The country has 7.8 million cattle and, in the late 1980s, about 8.2 million cubic meter of timber were cut yearly. Fishing is negligible, the annual catch being some 13,000 metric tons.²⁹¹ The

²⁸⁹ PCBAP, 1997

²⁹⁰ Encyclopaedia Britanica, 1980

²⁹¹ CIH, 1997

Paraguay River is practically the only transport route by which fish caught in the Paraguayan Pantanal can reach the capital, Asunción.²⁹²

Carron (2000) writes that the natives of the region support themselves through a combination of fishing, hunting, farming, cattle-raising, and by working for large cattle ranches or with timber companies. Intrusion by cattle farmers is eroding the lands held by native groups, whose main subsistence resource is fishing. Large properties formerly owned by timber companies that concentrated on extracting quebracho wood for use in tannin production are now being sub-divided, attracting people of Brazilian origin and placing further environmental and social pressures on the region.²⁹³

The Pilcomaya and Bermejo Rivers provide water for drinking, irrigation, fishing and mining in Bolivia, though seasonal droughts and flooding are problematic.²⁹⁴ Fishing itself is only a small component of the official Bolivian economy (total reported catch in 1995 of 6,300 tons: 0.04% of the GDP). Up to 40% of Bolivian fisheries have relied on a seasonal catch of migrating Prochilodus in the Pilcomaya River²⁹⁵, even though this fishery peaked in 1986 and the Bolivian Government now lists the fish stock as “vulnerable”. The fish are probably also substantially contaminated with lead contamination.²⁹⁶ Contamination from mining is a serious concern in the Pilcomaya River²⁹⁷, while erosion and siltation are of prime concern in the Bermejo.²⁹⁸

High Paraná

Geography, geology and river profile

The historical barrier to upriver fish movement in the Paraná River, and the traditional dividing point between the Upper and High Paraná River sections, is the Salto das Sete Quedas (Guaíra Falls) and canyon in the Serra de Maracuja of southeastern Brazil. However, due to flooding by

²⁹² Carron, 2000

²⁹³ Butler and Gaston, 1994. Cited in Carron, 2000

²⁹⁴ Mochek & Pavlov, 1996; Civic, 1999

²⁹⁵ Bayley, 1973; Espinach-Ros & Delfino, 1993

²⁹⁶ Mochek & Pavlov, 1996

²⁹⁷ Mochek & Pavlov, 1996

²⁹⁸ Civic, 1999

the Itaipú Reservoir, the functional barrier is now the Itaipú Dam, just upriver of the confluence with the Iguaçu River and the tri-national border corner of Brazil, Argentina and Paraguay. This is now also the logical start of the section of the river considered the “High” Paraná.²⁹⁹

The 1,944 km of river in this section³⁰⁰ flow southwest and then west, forming the border between Paraguay and Argentina from the Iguaçu River on. Flanked to the east by the Sierra de Misiones, it flows in a rocky river bed through patchy deposits of sedimentary material up to approximately Posadas. Tributaries that enter the river in this stretch include the Iguaçu, Urugua-í, Piray Mini, Piray Guazú, Paranay, and Capioví rivers from the west and the Acray, Monday, Nacunday and Tembey rivers from the east. All are characterized by falls close to their confluence with the Paraná, generally varying from 10–20 m in height (over 100 m for the Iguaçu) and limiting fish passage upriver from the mainstem. Of these, the headwaters of the Iguaçu and Urugua-í have been dammed.

At Posadas, the approximate half-way point of the High Paraná, the river bed turns west and broadens, with sections of anastomosing creeks and oxbows, floodplains and islands alternating with more restricted sections that pass through basaltic formations. The river bed here lies in an ancient alluvial fan, and varies between a shallow rocky base and sandy substrate. Vegetation in this area is alternately savannah grassland and mixed jungle, with a distinctive riparian zone along the river.

The large and controversial Yacyretá hydroelectric project crosses the river mainstem in the mid-section of the High Paraná. This dam is designed as essentially a run-of-the-river barrage, with a set reservoir height and very low retention time for water (3–7 days). It was equipped with two fish elevators to help mitigate effects on the fish populations in addition to navigation locks.³⁰¹ The top of the 70 km-long reservoir is just downriver of the cities of Posadas in Argentina and Encarnacion in Paraguay.

Climate in the High Paraná River Basin is sub-tropical, hot, and humid, with only a short dry season in the winter (July–August). Mean precipitation is 1.8 m/yr, with air temperatures that vary between approximately 0–40^oC and river water temperatures of 17–30^oC.³⁰²

²⁹⁹ Agostinho et al., 1995; Bonetto, 1998; García, 1999

³⁰⁰ García, 1999

³⁰¹ García, 1999

³⁰² García, 1999

Social characteristics

The areas around the High Paraná are used primarily for agriculture both in Argentina and Paraguay. Principal cities are Posadas in Argentina and Encarnacion in Paraguay, with smaller cities and fishing villages distributed along the river. Many of the fishing villages and indigenous communities on islands in the river were displaced by the Yacyreta development.³⁰³

Middle and Lower Paraná

Geography, geology and river profile

Below the confluence with the Paraguay River at Corrientes, the Middle Paraná turns south and runs through Argentina. It is a typical plains river in this stretch, banked by its own alluvial deposits and having an extensive floodplain on its eastern shore, with tracts up to 39 km wide. Its permanent bed, about four kilometers wide at Corrientes, also narrows to about 2,438 m at Bella Vista, about 2,100 m at Santa Fé, and about 1,830 m at Rosario in the lower river section. Throughout this stretch the river is strewn with chains of islands.

At Santa Fé the Paraná receives the last large tributary, the Salado River, and becomes the Lower Paraná. Between Santa Fé and Rosario the west bank rises as the river skirts the lowlands and turns to the east. This plains grassland flanks the river all the way to the delta at altitudes of 9 to 20 meters above the river. Due to the constant erosion of the west bank, which is higher than the east, the river becomes increasingly turbid and divided into many branches.

The delta of the Paraná begins as far north as Diamante (just south of Santa Fé), where the river begins to anastomose and turn southeast for the last 320 km into the Río de la Plata. About 18 km wide at its upper end, the delta is 64 km wide at its mouth. Covering 8,850 square kilometers in 1970, the Paraná delta appears to be advancing into the Río de la Plata at the rate of 70 m each year, due to an annual deposit of alluvial material estimated at 165 million tons. The most important branches in the delta are the two last great channels, the Paraná Gaçu and the Paraná de las Palmas. The islands of the delta, formed of the alluvial deposits, have

³⁰³ Inter-America Development Bank, 1997

consolidated embankments covered with trees, but are still submerged during times of high water.

Formerly the velocity of the Paraná changed frequently throughout its course. However, the construction of large hydroelectric reservoirs has turned the Upper Paraná River into a succession of lentic water bodies (see Chapter 2), and has modulated the variability of flow in the rest of the river to some degree.

The water level in the Middle and Lower Paraná nevertheless still fluctuates between two to six meters, depending primarily on rainfall in the upper basins. Flooding generally occurs from March to April, followed by a low water season from August to October. During the dry season, the lakes of the alluvial plain are isolated from the main river channel. Such environments provide food and shelter for a large number of fish species, and this portion of the river is possibly the most productive of the basin.³⁰⁴

About 25% of the total volume of water of the Middle Paraná comes from the Paraguay River. High water normally occurs in February or March in the headwaters, slowly coming south and reaching the border of the country Paraguay in June/July. Low water begins in November or December with similar downstream delays. The Upper Paraná and the Paraguay reach their maximum flows at different times. The mountainous basin of the Upper Paraná drains so rapidly that water begins to rise at Corrientes in November and peak in February, whereas the swamps of the upper basin of the Paraguay absorb floodwaters and keep them from reaching Corrientes until May. The consequence is that the flow of the Middle and Lower Paraná is moderated throughout the year, and floods extend over months rather than weeks.

Río de la Plata

Geography, geology and river profile

The Río de la Plata is a submerged saline estuary, though it is sometimes called a gulf. The rivers that enter the estuary drain about one-fourth of South America, so a large portion of the upper part is fresh enough to support large numbers of fresh-water fish species. Montevideo, the capital of Uruguay, is on the northern shore of the estuary, and Buenos Aires, the

³⁰⁴ Bonetto, 1998

capital of Argentina, is on the southern shore. From where the delta of the Paraná and the mouth of the Uruguay meet in the Río de la Plata, the open Atlantic lies about 290 km to the east. The mean annual temperature is 55^oF (13^oC) and monthly averages never go below 50^oF (10^oC). However, winter frosts are frequent in the south and can range as far north as Asunción in Paraguay, and Paraná State in Brazil.

Every year the Paraná and Paraguay rivers bring down about 56,620,000 cubic meter of silt. The winds and the tides keep the suspended material from settling quickly, so the deposits form great shoals, banks, or bars of clay, sand, and organic matter. The water volume discharged into the Atlantic by the Río de la Plata is estimated at 22,000 cubic meters per second. Water depth varies from 1.8 m above the shoals to 20 m in the intervening channels.

Although the water of the tributary rivers is so widely distributed over the length and breadth of the estuary that variations in their volume do not affect the water level, the level is considerably affected by tides and winds. Rainfall is copious in all seasons, amounting to 990 mm a year.

Social characteristics of the Middle & Lower Paraná and La Plata basins

Along these basins lie the Pampas, a lowland well suited for production of grains such as wheat, barley, oats and oilseed. Most of the Argentinean population of 18 million³⁰⁵ lives in these basins, together with industries such as petroleum, chemical and agro-industrial plants. Wastewater treatment varies regionally from individual to public septic tanks. The water of the estuary is exploited for urban and industrial purposes as well as for navigation. Fishing, except for that of the abundant detritivore curimbatá or sábalo (Prochilodus sp.), appears to be of little overall commercial importance, though in some areas local populations may rely on the activity for their livelihood.³⁰⁶

Habitats Used by Migratory Species

Migratory fishes use different habitats for food, for shelter and for reproduction. In the Upper Paraguay River Basin, the habitats used for

³⁰⁵ 1991 census

³⁰⁶ www.ramsar.org/profiles_argentina.htm

feeding are the floodable areas, temporary water courses, oxbow lakes along the rivers and large lakes found along the Paraguay River. The main river channel is used for migration and the headwaters for spawning.³⁰⁷

Bonetto and co-workers observed a similar pattern for the Middle and Lower Paraná River Basin and the Río de la Plata Basin.³⁰⁸ During the flooding season, the Paraná River overflows its valley and forms many shallow lagoons, where the young and juveniles of important migratory fishes such as Prochilodus platensis, Salminus maxillosus, and Pseudo-platystoma corruscans can be found.

For freshwater fishes, the Upper Río de la Plata can be considered a continuation of the Middle and Lower Paraná and the Lower Uruguay River, as indicated by the results of tagging experiments on the principal migratory species (such as the sábalo (Prochilodus lineatus), the boga (Leporinus obtusidens), the dourado (Salminus brasiliensis), the patí ( Luciopimelodus pati) and the common armado (Pterodoras granulosus)). This section of the Río de la Plata is an area of concentration for these species.³⁰⁹

MIGRATORY SPECIES AND MIGRATION PATTERNS

Most of the economically important fish in the Paraguay-Paraná River are migratory. Species that are widely distributed geographically include the characins P. lineatus, S. maxillosus, Piaractus mesopotamicus, species of the genus Leporinus (macrocephalus, friderici), Schizodon borellii, Brycon microlepis, Brycon orbignyanus and catfish such as P. corruscans, Pseudoplatystoma fasciatum, Paulicea luetkeni, Sorubim lima and Hemisorubim platyrhynchos. Some differences can be found in fish fauna composition through the entire basin, and economic importance of the migratory species varies regionally. For example, B. microlepis and the pacu-pevas of sub-family Myleinae are economically important only in the cities of Cuiabá and Várzea Grande in Mato Grosso State, North Pantanal.

One of the most striking features of South American fish assemblages is the abundance of detritivorous fishes. The most prominent of these is

³⁰⁷ Rondon, 1990; Resende et al., 1996a, 1996b; Resende & Palmeira, 1999; Lima et al., 1984a, 1984b

³⁰⁸ Bonetto et al., 1969, 1970, 1971, 1981

³⁰⁹ Nión, 1996

the curimbatá (P. lineatus),³¹⁰ which feeds on detritus resulting from flooding in shallow areas. Detritus makes up more than 77% of its food, with algae and other items making up the rest. The large catfish Pseudoplatystoma spp. is commonly seen feeding on P. lineatus when it begins to leave the flooded areas and large lakes in which it remains during the flood season. The catfishes appear to leave the flooded areas when their prey starts to migrate upstream.

In the Paraguay River Basin, the first species that begin to migrate upriver are the characins, of which the best known is P. lineatus. Large shoals of P. lineatus moving upstream can generally be seen from September to October in a migration known as the piracema. By the end of the dry season they have reached the headwaters of the rivers, where they wait for the first rains, which usually fall from December to February. Their spawning is famous for the noise made by the males during mating.³¹¹ In the warm river waters (generally 28^oC in the Pantanal rivers) the eggs hatch within 24 to 48 hours. Carried passively by currents, the larvae and fry enter flooded areas, where they feed and find shelter from predators (Figure 2).

FIGURE 2. Migratory fish life cycle in the Pantanal

³¹⁰ Resende et al. 1996a

³¹¹ Godoy, 1967; Bayley, 1973; Resende, personal observation

After spawning, the adults gather in preparation for downstream migraton in a phenomenon known as rodada. They then move slowly back to the downstream floodplains, arriving in very poor condition. From February to May or June, depending on the extent and duration of floods, they feed. By June or July they are again in good condition and ready to return upstream to spawn, leaving the draining floodplain in what is known as the lufada (characterized most markedly by large numbers of small forage fish). Figure 2 presents the relationships between the rivers, their laterally floodable areas and the yearly flood cycle. The large catfishes, such as P. corruscans and P. fasciatum, follow the characins, migrating to the headwaters and spawning from December to February.

Young migratory fish remain in the lower stretches of the rivers until they become adults. In the floodplain they can be found in the temporary water courses known as corixos and vazantes or in permanent water bodies such as lakes and lagoons or oxbow lakes. Mortality in this phase depends on how much water remains in the water bodies during the dry season.

Migratory routes of fish in the Paraná River Basin are incompletely known, though some trends have been hypothesised based on tagging studies, fisheries data, and biological studies of adults and larvae (Figure 3). The information suggests that extensive reproductive migrations may occur (one tagged dourado, S. maxillosus, travelled from the Rio Plata Estuary over 1,440 km to Posadas, in the High Paraná³¹²), but shorter routes are also likely. For example, migration of P. lineatus in the Pilcomaya River probably is restricted to the 450 km between the Andes foothills upstream of Villa Montes and the river’s floodplains in the Gran Chaco, without involving the Paraguay River mainstem³¹³; migratory stocks of the Pantanal probably only migrate between the headwaters of tributaries in the adjacent highlands and the Pantanal wetland³¹⁴; and the High, Middle and Lower Paraná River may contain several distinct sections with regards to migratory routes of fish.³¹⁵

The migratory fish species of the Paraná-Paraguay River Basin that are of importance to humans are primarily characids and silurids. In alphabetical order, the main species are:

³¹² Sverlij & Espinach-Ros, 1986

³¹³ Bayley, 1973

³¹⁴ Resende, unpublished

³¹⁵ Espinach-Ros & Delfino, 1993; Sverlij & Espinach-Ros, 1986; Oldani, 1994

Characids

Brycon spp.

B. microlepis, previously classified as B. hilarii, is endemic to the Upper Paraguay Basin. This fish is particularly appreciated in the cities of Cuiabá and Várzea Grande in Mato Grosso State, where several restaurants specialize in grilled pera, a popular local name for this fish (otherwise

FIGURE 3. Examples of migratory patterns of fish hypothesised for the Paraná River Basin deduced from tagging experiments and/or fisheries data³¹⁶

³¹⁶ Information presented is illustrative and likely to be far from a complete picture of migratory patterns in the basin; (1)–(4) adapted from Espinach-Ros & Delfino, 1993. (1) & (2) based on fisheries information and tagging experiments of dorado (S. maxillosus) by Sverlij & Espinach-Ros, 1986. (3) & (4) based on fisheries information and biological studies of sabalo (P. “platensis”) by Bayley, 1973; Payne & Harvey, 1989. No citation given for the Bermejo River information. (5) based on recent tagging experiments of the curimbatá (P. lineatus) by Agostinho et al., 2002; also see Chapter 2. (6) based on tagging experiments with curimbatá (P. “scrofa”) by Godoy, 1967 prior to the construction of recent dams. (7) is an example of migratory pattern of characids and silurids in the Pantanal, based on biological studies by Resende et al., 1996a; unpublished data.

known in Portuguese as piraputanga and in Spanish as salmón). The species is a good swimmer and comes to the surface in search of food. It is not uncommon to see it feeding on flowers that have fallen into the river from the riparian vegetation. The species is omnivorous.³¹⁷

B. orbignyanus occurs only in the Lower Paraná River. While not very abundant, the species has great sport fishing value. Its food habits are probably similar to that of B. microlepis.

Leporinus spp.

L. obtusidens, a characid known in Portuguese as piava and piapara and in Spanish as boga, is found throughout the Paraná-Paraguay Basin but not much is known of its biology in this area. It has an elongated body, and grows to a maximum size of around 40 cm. It normally weighs around 3 kg, though some specimens can grow to 6 kg. It inhabits both calm and running waters, and shelters among stones. Males and females in advanced stages of gonad development were captured in the Taquari River headwater falls, at Cachoeira das Palmeiras, in late September.³¹⁸ Vegetal remains were most abundant and frequent in the stomachs of fish captured in the Bento Gomes River, North Pantanal.³¹⁹

Leporinus macrocephalus has only recently been described as a new species. It is a large Leporinus species that occurs throughout the Paraguay Basin and in the Paraná River, but is less frequent in the Upper Paraná Basin. It grows to a length of about 60 cm or more, and can be found in flooded areas, though it prefers running water.³²⁰ It prefers a herbivorous diet,³²¹ but also feeds on crabs and freshwater aquatic snails, which are used as bait by fishermen. Vegetal remains were the only food found in the stomach of one specimen of L. macrocephalus caught in the Bento Gomes River, North Pantanal.³²²

Leporinus friderici, a third species of this genus, grows to more than 40 cm in length and occurs throughout the Paraná-Paraguay Basin. Little is known of its biology.

³¹⁷ Silva, 1990

³¹⁸ Resende, unpublished

³¹⁹ Mesquita, 1992

³²⁰ Resende, personal observation

³²¹ Resende et al., 1998

³²² Mesquita, 1992

Piaractus mesopotamicus

P. mesopotamicus, previously also known as Colossoma mitrei, is the most representative fish of the Pantanal and occurs in almost every part of the region during the high water period. Known in Portuguese as pacu-caranha, or simply pacu, and in Spanish as pacú, it is a large characid that historically was found throughout the whole Paraná-Paraguay Basin. However, it has been absent from the La Plata River since the 1980s, and according to Quiros (1993), had practically disappeared from the Lower Paraná River, as well as from the La Plata and Uruguay rivers, by the time of his report.³²³ It grows to 70 cm or more, with colours that can vary from almost black when in the flooded areas to bright yellow when in the river headwaters for reproduction. The body shape is oval to elliptical, and is distinctive by pronounced dentition capable of breaking hard fruits and seeds. It feeds on fruits, seeds and leaves of riparian vegetation and on crabs, molluscs and insects.³²⁴ For example, adults are commonly seen feeding on the fruit of the caranda palm during the flood season,³²⁵ and fruits and seeds of Mouriri acutiflora, a plant that grows in the floodable riverside areas, have been found in the stomachs of young fish during the flood season in Lake Acurizal of the Pantanal, in Mato Grosso State.³²⁶

Gonadal maturation of the pacu in the Upper Pantanal takes place from July to October, with spawning occurring in the river channel of the headwaters of the Cuiabá River in October-December, with a peak in November.³²⁷ Reproductive adults have also been captured in the headwaters of the Taquari River.³²⁸

In a study on trends in abundance carried out for the Brazilian Pantanal, Agostinho et al. (unpublished) found that P. mesopotamicus is overexploited. Starting in 1994, to manage this overexploitation, the minimum capture size was increased by the Mato Grosso do Sul State government from 40 to 45 cm. At the time of the study P. mesopotamicus became the most captured fish, overtaking Pseudoplatystoma spp. In the Lower Paraná River, fishing for this species is currently prohibited entirely.

³²³ Quirós, 1993

³²⁴ Silva, 1985

³²⁵ Resende, unpublished

³²⁶ Conceição, 1988; Silva, 1985

³²⁷ Lima et al., 1984a, 1984b

³²⁸ Resende, unpublished

Prochilodus spp.

Known in Portuguese as curimbatá, and in Spanish as sábalo, P. lineatus is also known as P. platensis in Argentina.³²⁹ A second species, Prochilodus scrofa, is found in the Upper Paraná Basin, though the taxonomic distinction from P. lineatus is controversial. P. lineatus is widely distributed throughout the Paraná and Paraguay basins, and clearly represents the majority of the fish biomass. Bonetto et al. (1970) estimated a standing stock of 1,100 kg/ha of sábalo for the mid-region of the Paraná River: over 60% of the total fish biomass. In the review for the proposed Hidrovia project³³⁰, this was one of the migratory species most captured in the Middle Paraná Basin by traditional commercial fishermen in the Puerto Bajada Grande, Puerto Sanchez and Corrientes regions. The fish has also been important for fisheries in the Brazilian Pantanal, but in 1994, the fishing and commercialization of P. lineatus was prohibited in Mato Grosso do Sul for conservation purposes (see below).

Resende et al. (1996a) studied P. lineatus in the Upper Paraguay. In the Miranda-Aquidauana River system of this area, it is clear that only adults migrate to the headwaters to spawn, with young adults probably migrating later in the season than the older fish. Reproductive migration begins with rising water levels as early as September and October, but spawning only occurs later, usually between December and February. The timing of peak spawning varies from year to year depending on the rains in the river headwaters.

In the Pilcomayo River, a tributary of the Middle Paraguay,³³¹ “P. platensis” migrates approximately 450 km upstream from the Gran Chaco floodplain into the river headwaters, where it has been observed spawning in large schools in a narrow, shallow, but slow-moving and mud-bottomed tributary in October-November. Peak migratory activity at Villa Montes, on the border of the Andes foothills with the Chaco, is seen earlier, in July/August, also with young adults in later schools. Spent fish move downriver again with the first major floods at the end of November– December. This species grows to six to seven years of age in this system, becoming reproductive at two and a half to three years.

³²⁹ Cabrera and Candia, 1964; Cordiviola, 1971

³³⁰ CIH, 1997

³³¹ Bayley, 1973

In the La Plata River downstream of Buenos Aires,³³² both migratory and resident “P. platensis” have been described. Migratory fish are smaller (maximum size of 40 cm vs. 72 cm for resident fish) and reported to move south in the summer and north in the winter.

Salminus maxillosus

The sub-family Salmininae of the Characidae is represented by only one genus and one species in the Pantanal, S. maxillosus. Its common names, dourado in Portuguese and dorado in Spanish, are due to its golden colour. It grows to a length of one meter or more, and is highly prized by sport and commercial fishermen alike. It is one of the few South American fish widely recognized by the international sport fishing community. A very active predator, it feeds on any fish it can capture. It occurs throughout the Paraná-Paraguay Basin, although catches have been decreasing since the late 1940s throughout the lower basin in Argentina, despite restrictions on commercial fishing. Conflicts between sport and commercial fishermen have been increasing, and the trophy size of Salminus has been decreasing at the confluence of the Paraná and Paraguay rivers, though total fishing effort seems not to have increased.³³³

Principal prey of S. maxillosus in the La Plata River has been reported as the small catfish Parapimelodus valenciennesi, whereas in the Lower Uruguay the fish preyed primarily on the detritivorous characids P. platensis, Curimata sp. and Lycengraulis olidus.³³⁴ The authors in these areas found only immature or non-reproductive S. maxillosus, but this included fish of up to 6 years of age.

In the Miranda River of the Upper Paraguay region, young S. maxillosus in oxbow lakes were preying on small fish (Trachydoras paraguayensis, Serrasalmus marginatus, and Crenicichla lepidota) and Macrobrachium spp. shrimp.³³⁵ While migratory patterns in the Pantanal are not well known, reproductive adults have been captured in the headwaters of the Taquari and Miranda rivers. Fish tagged in the La Plata River in March moved throughout the estuary, but one tagged in December of the study year migrated 1,440 km up the Paraná River to

³³² Cabera & Candia, 1964

³³³ Quirós, 1993; Sverlij & Espinach-Ros, 1986

³³⁴ Sverlij & Espinach-Ros, 1986

³³⁵ Resende et al., 1996b

Posadas.³³⁶ Cordiviola (1966) reports that female dourado in the Middle Paraná tend to be larger and older than the males. Migration in the Paraná River may extend up to 1, 400 km, From the Rio Plata to the High Paraná,³³⁷ but is probably more restricted in general.³³⁸

Schizodon borellii

This abundant characid, related to the Leporinus spp., is known in Portuguese as ximboré and in Spanish as piava. It is an herbivorous fish, feeding on vegetation, roots, and other plant parts in the southern³³⁹ and northern Pantanal.³⁴⁰ While common and a prominent component of migratory schools in rivers of the area, the fish is not highly prized for food. However, it is considered by some as a possible alternative to the grass carp for control of aquatic vegetation.

Silurids (catfish)

Hemisorubim platyrhynchos

H. platyrhynchos, known in Portuguese as jurupoca and in Spanish as tres puntos, occurs throughout the Paraná-Paraguay River Basin, with the exception of the Rio de la Plata. It grows to 50 cm in length and feeds mainly on fishes. As with S. lima, very little is known about its biology. Fish swallowed whole were the main food of H. platyrhynchos in the oxbow lakes of Lower Miranda River.³⁴¹ In the Taquari River headwaters, males and females with ripe gonads have been found from late October to the beginning of December.³⁴²

Paulicea luetkeni

P. luetkeni, known in Portuguese as jaú and in Spanish as manguruyú, is the largest of the catfishes in the Paraná-Paraguay Basin. It has practically disappeared from the Lower Paraná River, as well as from the La Plata River and Uruguay rivers.³⁴³ It has been absent from the La Plata River

³³⁶ Sverlij & Espinach-Ros, 1986

³³⁷ Sverlij & Espinach-Ros, 1986

³³⁸ Espinach-Ros & Delfino, 1993

³³⁹ Resende et al., 1998

³⁴⁰ Mesquita, 1992

³⁴¹ Resende et al., 1996b

³⁴² Resende, unpublished

³⁴³ Quirós, 1993

Basin since the 1980s. No biological studies are available about this species in the Paraná-Paraguay River Basin, but commercial fishermen indicate they can be captured in the deepest parts of the river. The species is known to be piscivorous. In a study by Agostinho et al. (unpublished) the species was found to be overexploited in the Brazilian Pantanal, and its fishing is prohibited in the Lower Paraná.

Pimelodus spp.

Pimelodus spp., small catfish know in Portuguese as mandi and in Spanish as bagre, are important to the Paraná River fishery.

Pinirampus pirinampu

P. pirinampu, known in both Portuguese and Spanish as patí, is important to the Paraná River fishery (see Chapter 2 for description).

Pseudoplatystoma spp.

P. corruscans, the catfish know in Portuguese as surubim and in Spanish as surubí, is found throughout the Paraná-Paraguay Basin. P. corruscans is becoming scarce in La Plata River, where captured individuals never exceed 60 cm in total length.³⁴⁴ It is one of the migratory species most captured in the Lower Paraná Basin. The adults are usually found in the main river beds while their young remain in the corixos and small rivers. Generally these fish migrate upriver following shoals of P. lineatus (curimbatá) from October to December, which form their main food in this season. On the other hand, Cordiviola (1966) reports that this species migrates upriver in the Middle Paraná starting in March, with males migrating before females, and the downstream movements occur in spring (December).

P. fasciatum, known in Portuguese as cachara and in Spanish as surubí atigrado, is a catfish that is very similar to the surubim, but is not found in the Upper Paraná River Basin, and is becoming scarce in La Plata River. In the Pantanal it frequents the same habitats as P. corruscans, but, according to experienced fishermen, prefers to stay near submerged tree trunks and branches. As with P. corruscans, captured individuals never exceed 60 cm in length in the Lower Parana Basin, though the species is known to grow to over one meter in length in the Upper Paraguay Basin.

³⁴⁴ Quirós, 1993

Pterodoras granulosus

P. granulosus, a medium-sized thorny catfish known in both Portuguese and Spanish as armado, contributes to the fisheries in the Paraná River (see Chapter 2 for description).

Sorubim lima

S. lima is a small catfish found in the Paraná and Paraguay rivers, some zones of the Bermejo, in the zone of confluence with the Paraguay River, and in small interior tributaries of the large rivers. It can grow to 50 cm and 2 kg. The species is carnivorous, preferring crustaceans and small fish: fish and shrimp were found in stomach contents of S. lima captured in the oxbow lakes of the Lower Miranda River.³⁴⁵ It is also one of the migratory species most captured in the Lower Paraná Basin. In the Taquari River headwaters, males and females with ripe gonads arrive by late October.³⁴⁶

IMPACTS ON MIGRATORY SPECIES

Fisheries

Fishing in the Pantanal

Fishing is a traditional activity in the Pantanal. The first people to fish were the native Indians. When the bandeirantes arrived, they also used fish as a protein source. Total consumption at this time was very low, and there was no export.

The fish harvest today varies regionally in the Paraguay-Paraná River Basin. Fishing effort is generally greater near the big cities such as Cáceres, Corumbá and Porto Murtinho in the Paraguay River in Brazil. Concepción, Asunción, Villeta, Alberdi and Pilar are the largest fishing ports in Paraguay; Corrientes, Paraná, Rosario and Buenos Aires are the largest freshwater fishing ports in Argentina; and Villa Montes is the main fishing port in Bolivia. Fishing also takes place on the Pilcomayo River in Bolivia.³⁴⁷

The first published report on fish and fisheries in the Pantanal was by

³⁴⁵ Resende et al., 1996b

³⁴⁶ Resende, unpublished

³⁴⁷ Bayley, 1973

Aguirre (1945), who gave an account of the methods used by local populations, such as hooks on lines hung from river shorelines or from small boats, and the bows and arrows used by the local Indians. Only in Aricá, a small settlement, did fishermen use a kind of trawl net of 50 to 100 m, to catch piraputanga (B. microlepis), pacu-pevas (Mylossoma paraguayensis, M. orbignyanum and some Metynnis spp.), curimbatá (P. lineatus) and other species. In some stretches of the Cuiabá River local fishermen put manihot or corn into the river to attract fish.

In the 1970s, when the federal government built roads between the west-central and the southeastern regions of the country (including São Paulo State), fishing began to increase. Table 1 gives an idea of the evolution of fish consumption in Cuiabá fish market and exports to other parts of Brazil. In 1980, half of the production was consumed locally and half was exported; but by 1983, about 70% of the catch was exported to other states (Table 1), mainly to São Paulo and Goiás State. These are the only statistics available for the part of the North Pantanal that lies within Mato Grosso State.

TABLE 1. 1980–1983 fish landings in and exports from Mato Grosso State³⁴⁸

The catches summarised in Table 1 were captured mainly in the Cuiabá River, along a stretch of 139 km between Barra do Aricá and Guia, fished throughout most of the year. In the flood season the captures came from the Lower Cuiabá River, where the fish feed in the flooded areas. Local traditions assign fishing rights to particular fishing points and times that are traded or passed from generation to generation. The Cuiabá area is also distinguished by the use of traditional preservation methods. Because they have no ice, the fishermen use large jacás - baskets made of bamboo and suspended in the river to keep fish fresh up to the time of sale.

³⁴⁸ Lima & Chabalin, 1984

When Mato Grosso do Sul State was created in 1979, the INAMB (Instituto de Controle e Preservação Ambiental) was formed and made responsible for the regulation and control of environmental issues, including the monitoring of fisheries. Fish statistics from 1979 to 1983³⁴⁹ and from 1979 to 1984,³⁵⁰ based on records of transport of commercially captured fish, are shown in Tables 2 and 3.

Most of the fish during this period were caught commercially for local consumption or for export mainly to São Paulo State. The two large Pseudo-platystoma species were the most captured, followed by P. lineatus. For 1982 to 1984, local consumption increased from 48 to 61%. However, concerns of overexploitation resulted in the prohibition of gillnets for commercial

TABLE 2. Species contribution to 1979–1983 fish landings from the Pantanal³⁵¹

TABLE 3. Utilization of 1979–1984 fish landings from the Pantanal³⁵²

³⁴⁹ data of Vieira, 1986, published in Silva, 1986

³⁵⁰ Resende, unpublished

³⁵¹ Fisheries data collected by Vieira, 1986; published in Silva, 1986

³⁵² Resende, 1986, unpublished

fishing in 1986 and the restriction of cast nets to the P. lineatus fishery.

In 1986 INAMB was shut down and fisheries statistics were no longer collected. Fish data collection did not start again in Mato Grosso do Sul until 1994, and then only after a great effort. From 1994–1998 P. mesopotamicus became the most captured fish, overtaking Pseudoplatystoma spp. (Table 4). In the 1990s, the fishing systems prevailing in the region also changed. Sport fishing expanded to become the second most important economic activity in the Pantanal, with an annual value of more than R$ 60 million. In Corumbá City, there are now almost 70 fishing hotel boats for sport fishermen. More and more, cities like Corumbá, Miranda, Aquidauana and Porto Murtinho are largely dependent on sport fishing, and the same is happening in Mato Grosso State to the north. From 1995

TABLE 4. Species contribution to sport fishing in the Pantanal, 1995–1998³⁵³

³⁵³ Sistema de Controle de Pesca de Mato Grosso do Sul, Embrapa Pantanal/Sema-MS/Polícia Florestal-MS

to 1998, commercial fishing decreased to 13.5% of the total fish catch in Mato Grosso do Sul (Table 5). In 1994, the fishing and commercialization of P. lineatus was also prohibited in Mato Grosso do Sul.

Figure 4 summarizes fisheries data available for the Pantanal, covering the period of 1979–1998. Commercial fishing predominated in this period

TABLE 5. Total fish landings from the Pantanal, 1995–1998³⁵⁴

FIGURE 4. Fish landings in South Pantanal, by fish species³⁵⁵ and year³⁵⁶

³⁵⁴ Sistema de Controle de Pesca de Mato Grosso do Sul, Embrapa Pantanal/Sema-MS/Polícia Florestal-MS

³⁵⁵ Surubim/Pintado: combined catch of P. fasciatum & P. corruscans; jaú: P. luetkeni; Dourado: S. maxillosus; pacu: P. mesopotamicus; barbado: P. pirinampu; curimbatá: P. lineatus; piranha: Pygocentrus nattereri; paivaçu: L. macrocephalus

³⁵⁶ Fisheries data of Vieira (1986), published in: Silva, 1986; Sistema de Controle de Pesca de Mato Grosso do Sul, Embrapa Pantanal/Sema-MS/Polícia Florestal-MS

until 1984. In these years, gear such as cast nets and gillnets were used for commercial fishing; drift gillnets were very efficient at capturing large catfishes such as pintado and cachara (Pseudoplatystoma spp.), while cast nets were efficient at catching P. lineatus. Unfortunately we have no data from 1984 to 1995, the years in which the transformation from commercial fishing to sport fishing occurred.

Presently in both Mato Grosso and Mato Grosso do Sul, only hook and line and rod and reel can be used to catch fish for both commercial and sport fishing. Following the 1986 prohibition of drift gillnets, cast nets were banned in 1994. Small-mesh cast nets can be used only by commercial fishermen and then only to catch bait.

Illegal fishing is known to take place in the Pantanal, mainly in the Taquari River Basin in the South Pantanal. Based on spot surveys, E. Resende (unpublished) estimates that the same amount taken by the legal fishery (~170 tons/year) is taken from this river illegally. No further estimation of the degree of illegal fishing is available.

Non-Brazilian fisheries

In Argentina, the total fish catch for the Paraná River from 1945–1984 was estimated as 3,979 tons/year, of which P. lineatus comprised 40%, and for the Río de la Plata 11,119 tons/year, of which P. lineatus comprised 73%.³⁵⁷ Data from the Instituto Nacional de Estadistica y Censos, Anuario 1993 (Table 6) show fish landings ranging from a minimum of 8,024 tons in 1989 to 11,777 tons in 1990. In 1990, 39% of the fish came from the Paraná River (including the Paraguay River), 30% from the Río de la Plata and 21% from the Uruguay River. The data from 1976 (Table 7) differed slightly from 1990. In 1976, 50% came from the Paraná River, 26% from the Río de la Plata and 23% from the Uruguay.

TABLE 6. Fluvial and lacustrine fish landings in Argentina³⁵⁸

³⁵⁷ Quirós & Cuch, 1989

³⁵⁸ Instituto Nacional de Estadistica y Censos; cited in CIH, 1997 (vol 4)

TABLE 7. Fresh-water fish production in Argentina, from rivers and provinces, 1976³⁵⁹

Espinach-Ros and Delfino described the fisheries of the Paraná and Paraguay rivers outside of the Pantanal and the Upper Paraná (see Chapter 2), as they existed in 1993, for the different river sections³⁶⁰:

In the High Paraná River, upstream of Posadas, Argentinean commercial fishing is not very intense (40–50 fishermen over 360 km), carried out primarily with a variety of types of longlines. Smaller catfish species (Pimelodus spp.) and boga (L. obtusidens) are captured along the river margin, while dourado (S. maxillosus), pacu (P. mesopotamicus), patí (Leucopimelodus pati), surubí (P. fasciatum), and manguruyú (P. luetkeni) are captured in the main channel. Sábalo (P. lineatus) and baitfish are caught with cast nets and gillnets in shallow water. Catches in the 1980’s were about 2,000 kg/yr/fisherman, with an increase as the Itaipu Dam was completed. The catch has since declined, coinciding with the completion of the Yacyretá Dam. Paraguayan commercial fishing in this area is carried

³⁵⁹ Instituto Nacional de Estadistica y Censos and the Anuario, 1993; cited in CIH, 1997 (vol. 4). 1976 is the only year for which this breakdown of total landings is available.

³⁶⁰ Espinach-Ros & Delfino, 1993

out with rod and reel and boats powered with outboard motors, targeting primarily dorado and surubí, but also catching some pacu. The activity increased with the construction of the Yacyretá Dam, with 160 fishermen registered by 1991. Productivity for Paraguayan fishermen in this area averaged 42–160 kg/day/fisherman in the late 1980s.

From the Yacyretá Dam to the confluence with the Paraguay River the High Paraná is mostly taken up by sport fishing reserves, and commercial fishing is not significant. Sport fishing is particularly intense below the Yacyretá Dam, outside of the 3 km safety perimeter.

Commercial fishing in the Middle Paraná River, between the Paraguay River and Diamantes, is also limited by sport fishing reserves to a 140 km stretch downstream of the confluence of the two rivers and small stretches near the cities of Helvecia, Paraná, and Diamantes. The activity is most active in the first of these stretches, near Corrientes and Barranqueras, with 200 to 250 registered fishermen in 1992. The commercial fishing at the time of the report targeted primarily catfish, working out of canoes with small inboard motors with the mallón net³⁶¹ in stretches of the mainstem river clear of obstacles (canchadas) and a variety of longlines in shallower water. Catch in 1992 averaged 3,000 kg/yr/fisherman, with 90% represented by surubim and patí and 10% by 10 to 16 other species. Sport fishing in this stretch is quite intense, with 6,500 licences issued in the Corrientes province in 1992, targetting dourado, surubí, and pacu, and, by 1997, up to 5,000 fishermen on the river every weekend.³⁶² At present, dorado fishing in the vicinity of the city of Corrientes is one of the principal internationally recognized sport fishing activities of South America, and is the site of numerous fishing derbies with international participation.

Commercial fishing in the Lower Paraná River has two components: a hook and line fishery in the river channel for catfishes (surubí, armado comun and patí) and the boga (L. obtusidens), and a net fishery in the floodplains for the sábalo (P. lineatus). Both are most active during the upstream migrations of the fall and winter. The river channel fishery is concentrated near cities, primarily Rosario (with 200 registered fishing families in 1991). A variety of long-line techniques are employed, depending on the species and environment. The floodplain fishery is

³⁶¹ A coarse gillnet that is either set or dragged along the bottom of the river

³⁶² CIH, 1997

concentrated in the province of Entre Lagos near the city of Victoria, with an estimated 174 active fishermen in 1990 (423 licensed fishermen) landing 1,580 kg/month/fisherman (95% sábalo). Similar numbers of commercial licences for net fisheries were issued in 2000 and 2001 (491 and 450, respectively), with approximately an additional 200 commercial licences for hook fisheries in each year.³⁶³ The trammel net³⁶⁴ was reported as the most common gear for this area in the early 1990s, either towed behind canoes or set overnight³⁶⁵, but simple gillnets and hook and line are also used, and the mallón gillnet, rather than the trammel net, is currently listed officially as the most common commercial gear for artisanal fisheries in this province.³⁶⁶ Commercial fishing is mostly seasonal or part-time (25–90% dedication),³⁶⁷ supplemented primarily by tending cattle and hunting. Nevertheless, the sábalo landings for the province of Entre Lagos, primarily through the port of Victoria, increased in the early 1990s from about 1000 tons to 5–8,000 tons in the second part of the decade (depending on the year) with an increasing proportion being exported, primarily to Brazil and Bolivia.³⁶⁸ Sport fishing is also increasingly important in the Lower Paraná River, with the number of licences issued increasing from about 5,500 in 1997 to about 7,500 in 2000.³⁶⁹ About 25% of these are for out-of-province licensees.

The freshwater fishery of the Plata River has been dominated in the past by beach seine and purse seine fisheries for sábalo (P. lineatus) for production of fishmeal and fish oil. At its peak in the 1940s, this fishery landed about 11,100 tons annually and supplied 10 processing plants. However, despite a brief resurgence in the 1980s, this fishery has ended, at least in part due to contamination from agricultural and industrial pollution. A comparable fishery continues in the Lower Uruguay River (see Chapter 4). A cast net fishery for sábalo and boga by the perjerry fishing fleet in the Plata River during their off-season also peaked in the

³⁶³ www.entrerios.gov.ar/produccion/dpesc07.htm

³⁶⁴ Three-layered gillnets with small-meshed inner panels sandwiched between two coarser-meshed panels. These nets are particularly efficient, as they entangle fish between the panels, but are controversial in that they also catch many small fish. They are called tres telas in Portuguese and tresmallas in Spanish.

³⁶⁵ Espinach-Ros & Delfino, 1993

³⁶⁶ www.entrerios.gov.ar/produccion/dpesc07.htm

³⁶⁷ Espinach-Ros & Delfino, 1993

³⁶⁸ www.entrerios.gov.ar/produccion/dpesc07.htm

³⁶⁹ www.entrerios.gov.ar/produccion/dpesc07.htm

1950s, and had been reduced to less than a third (10–15 boats) by the early 1990s.³⁷⁰ Hook and line fisheries for other species (primarily dourado, pacu, and catfish species) have shown a similar trend, purportedly due to reduced number and size of high-value species.³⁷¹ By 1997, the Argentinean fisheries in the La Plata River were reduced to three traditional fishing families with less than 50 people dependent on commercial fisheries,³⁷² though sport fishing has continued and is expanding. A small commercial fishery continues on the Uruguayan shore for the higher-priced freshwater species³⁷³, in part as a supplement to the estuarine fishery for croaker (Micropogonias furnieri).³⁷⁴

Paraguayan fisheries were studied by Bayley in the early 1980s³⁷⁵ and by Espinach-Ros and co-workers in the early 1990s.³⁷⁶ Bayley estimated landings of 16,000 tons per year, based on a survey of fish consumption in communities on the Paraguay and Parana rivers. Earlier surveys indicated substantially lower consumption in 1965 and 1978,³⁷⁷ but Bayley found that while fish consumption close to the rivers was increasing, it continued low throughout much of the country in 1984, probably due to both distribution problems and continued dietary preference for red meat. Espinach-Ros and co-workers report that, in the early 1990s, the fishery of the Paraguay River was expanding.³⁷⁸ According to these authors, the principal gear used is the mallón,³⁷⁹ dragged along the bottom in clear stretches of the river or left as gillnets in tributaries when the water is too high for fishing the mainstem. Mesh size of the nets varies with area being fished, with smaller mesh sizes used in the more intensely fished vicinity of Asunción. A variety of hook and line devices are also used, and cast nets are used to catch bait-fish. Larger-bodied fish are targeted, with, in the early 1990s, Pseudoplatystoma spp. representing about 50% of the landings.³⁸⁰ Similarly, the CIH survey in 1997 reported approximately

³⁷⁰ Espinach-Ros & Delfino, 1993

³⁷¹ CIH, 1997

³⁷² CIH, 1997

³⁷³ Espinach-Ros & Delfino, 1993

³⁷⁴ Wells & Daborn, 1997

³⁷⁵ Bayley, 1984

³⁷⁶ Espinach-Ros et al., 1991

³⁷⁷ Min. de Salud Publica, 1978. Cited in Bayley, 1984

³⁷⁸ Espinach-Ros & Delfino, 1993

³⁷⁹ Coarse gillnet set or dragged along the bottom

³⁸⁰ Espinach-Ros & Delfino, 1993

1,000 commercial fishermen in the vicinity of Asunción and 430 in the vicinity of Concepción, fishing surubí (Pseudoplatystoma spp.), dourado (S. maxillosus), manguruyú (P. luetkeni), pacu (P. mesopotamicus) and boga (Leporinus spp.). Brazilian fishermen from Porto Murtinho also contribute to the fishery in this stretch of the Paraguay River, but little data is available on their activity.

Sport fishing is popular in the Asunción region, through eight Clube de Pesca associations that lease boats and equipment to their members. More than 200 are out on a typical weekend, with 2 to 4 persons per boat. In Concepción, sport fishermen tend to use private boats and gear, and prefer large catfish, providing a market for live bait fish.³⁸¹

The Bolivian fishery for migrating sábalo (P. lineatus) of the Pilcomayo River has probably been the most important single fishery of the country, at one time representing over 40% of the national landings.³⁸² The fishery started as a traditional trap fishery in the Villa Montes region, based on fish traps made with rocks.³⁸³ The fishery was updated in the 1960s to include beach seines and expanded to the downstream floodplains.³⁸⁴ Landings increased substantially with this technology, but peaked at about 2,000 tons in 1986³⁸⁵ and gradually declined to an all-time low in 1998.³⁸⁶ This population of Prochilodus was listed as vulnerable in 1993 by the Bolivian government,³⁸⁷ but is apparently also substantially contaminated by heavy metals.³⁸⁸ Other species fished commercially in the area include the boga (L. obtusidens), Pimelodus sp. catfish, the dourado (S. maxillosus), the surubí (P. corruscans), and the pacu (P. mesopotamicus).³⁸⁹ Fisheries for the sábalo and up to 70 other species in the Chaco reaches of the Lower Pilcomayo and Berjemon rivers are also important to indigenous Wichi tribes of northern Argentina³⁹⁰, who make seasonal use of migrating schools, at times fishing with traditional cactus-fibre nets.³⁹¹

³⁸¹ CIH, 1997

³⁸² Payne & Harvey, 1989

³⁸³ Bayley, 1973;

³⁸⁴ Payne, 1986. Cited in Espinach-Ros & Delfino, 1993

³⁸⁵ Payne & Harvey, 1989

³⁸⁶ Mochek & Pavlov, 1996

³⁸⁷ Camacho, 2002

³⁸⁸ Quevillon et al., 1995

³⁸⁹ Espinach-Ros & Delfino, 1993.

³⁹⁰ Barbaran, 2000

³⁹¹ Lindsay, 2002

Trends in abundances

One of the few studies on trends in abundance in the Parana-Paraguay Basin is that of Agostinho et al. (in preparation) that has been carried out for the Pantanal in Brazil since 1994. Using the statistical data from the Fishing Control System of Mato Grosso do Sul (SCPESCA/MS) and the Schaefer model for the maximum yield, they found that the pacu (P. mesopotamicus) and the jaú (P. luetkeni) are overexploited. To manage this overexploitation, the minimum capture size was increased in Mato Grosso do Sul from 40 to 45 cm for P. mesopotamicus and from 90 to 95 for P. luetkeni. It is highly probable that the same trend towards overfishing is true in Mato Grosso, but no further data were found for the rest of the river basin.

For other species there is no concrete evidence of overexploitation, though both commercial and sport fishermen are complaining that fish are disappearing. For example, the rodada and lufada phenomena, which were common in the past, particularly in the northern Pantanal, are now rarely seen.

Other Impacts

Impacts in the Upper Paraguay

It is generally believed that in floodplains such as the Pantanal, fish production is directly related to flooding. Years of high flooding lead to high fish production and years of low flooding lead to low fish production. However, the magnitude of floods is unpredictable. From 1960 to 1974, the Pantanal had a long period of reduced flooding, but at that time the fish stocks were not as exploited as they are today. In 1998 and 1999, the flooding was also very low. The consequences of long-term low flooding could be an economic disaster for the local human population and a major disruption of fish feeding and reproductive patterns.

The Upper Paraguay River Basin Conservation Plan (PCBAP), co-ordinated by IBAMA, outlines five main problems in the region: sedimentation, dams and dyking, water contamination, illegal fishing, and large-scale works (river dredging and the liquid gas pipeline that crosses the Pantanal).³⁹² Most development impacts on migratory fish in

³⁹² Lima Barros Dolabella, 2000

the Upper Paraguay Basin are caused by agricultural development, especially in the highlands. Roads that open up areas for settlement also lead to the cutting of gallery forests, resulting in erosion. The lack of soil conservation techniques causes soil erosion and consequent silting of the rivers in the Pantanal, raising the river bed, changing the river courses, and leaving large bodies of perennial standing water where formerly the land was dry enough during the dry season to allow cattle to graze.

Gold mining in Mato Grosso State is concentrated in the city of Poconé and diamond mining in the cities of Diamantino and Alto Paraguay. Both areas lie in the headwaters of the Paraguay River. Mercury contamination has been identified as problematic in the Poconé area, though natural levels may be high in some lagoons.³⁹³ The government of Mato Grosso is working on regulatory means to minimise the environmental impact of mining wastes. Water quality is also threatened in particular by population growth, especially around large cities like Cuiabá and Várzea Grande, which dump untreated waste directly into the Cuiabá River. In Concepción the urban houses use septic pits for wastewater, and in Asunción wastewater goes into a public septic pit.

Impacts in the Pantanal

The Pantanal is almost unaltered by development, without structures such as dams or reservoirs. The only hydroelectric dam is on the Manso River, a tributary of the Cuiabá River in the highlands. This dam was recently finished and closed during the 1999/2000 fish reproduction period (piracema). The immediate effect of this closure on the fish population appears to have been substantial, but long-term effects on the area’s ecosystem are not yet known.

There are, however, potential problems in addition to hydropower development. One is the liquid gas pipeline running across the Pantanal from Bolivia to Brazil, whose first phase concluded in February 1999. A major leak from this pipeline could have severe impacts on the Pantanal³⁹⁴, but safety features of the pipeline make such a leak very unlikely. The Hidrovia project that proposed opening up over 3,442 km of the Paraguay and Paraná rivers for navigation of barge convoys has now been abandoned due to public protest and predicted environmental

³⁹³ Tümpling et al., 1995

³⁹⁴ Lima Barros Dolabella, 2000

impacts. It was felt that draining of the Pantanal wetlands, which would arise as a consequence of the faster currents achieved by deepening the channels and blasting obstructions, would lead to erosion, water contamination, the disruption of natural communities and natural cycles, and that the long-term costs of these alterations would outweigh the economic gains from lower shipping costs. It was also predicted that flooding would worsen significantly downstream, as the two-to-three-month delay between the Paraguay River’s flood peak and the Paraná River’s flood peak (due to the buffering capacity of the wetlands) would be reduced. Water quality for the millions of people downstream would also likely worsen due to the destruction of the natural sewage-treatment capacity of the wetlands. Fisheries, of course, were also expected to be damaged.

Gottgens (2000) considers that despite the cancellation of the Hidrovia project, other smaller, isolated hydrological projects to dredge the Paraguay River and its tributaries may have cumulative effects that are worse than those foreseen in the original mega project. Despite opposition to the environmental destruction, various interests continue to push for a commercial waterway into the Pantanal. While it appears that no single all-embracing decision will be made for development, many small decisions may have the same environmental effect.³⁹⁵ Destruction of the Pantanal will most likely occur if local inhabitants are given no sustainable options for development.

The PCBAP study concluded that the economic activities best suited to the Pantanal are cattle-raising on the natural pastures, and sustainable tourism, fishing and hunting.

Impacts in Argentina

In Argentina most fishery problems are related to water pollution and degradation caused by development along the Paraná River. Quirós (1993) studied impacts on the fishery in the Rio de la Plata system and concluded that the evidence pointed to impacts from toxic substances used in agriculture and industry. Relatively high levels of heavy metals and agricultural pesticides were found in fish tissues and periodic massive fish kills were reported from the Lower Paraná Delta and the Rio de la Plata. Low oxygen levels and massive fish kills were also found in the

³⁹⁵ Gottgens, 2000

Lower Paraguay River. No water quality data are available for the Upper Paraguay Basin.

Quirós also writes that fruit and seed eating species of the genera Colossoma (now Piaractus) and Brycon and the large catfish P. luetkeni have disappeared from the Lower Paraná River, and from the La Plata and Uruguay rivers. According to Quirós, marine fish species of the Basilichthys and Lycengraulis genera, which usually move upriver in winter, have also practically disappeared from the commercial catches in the Middle Paraná. As well, although commercial fishing for S. maxillosus has been highly restricted, this species has been decreasing in catches since the late 1940s throughout the lower basin. The size of the large catfish of the Pseudoplatystoma genera has been decreasing for the last three decades in the Lower Paraná. Conflicts between sport and commercial fishermen have been increasing, and the trophy size of Salminus has been decreasing at the confluence of the Paraná and Paraguay rivers, though total fishing effort seems not to have increased.³⁹⁶

Studies of the effects of the Yacyretá Dam on fish have recently been published, demonstrating reduced energy stores and sexual development in detritivorous fish at the base of the dam, compared to stations further downriver.³⁹⁷ Mortality from gas bubble disease has also been reported,³⁹⁸ and significant pollution from slaughterhouses in Encarnacion may be problematic.³⁹⁹ Original artisanal fisheries and fishing communities were disrupted by the hydroproject,⁴⁰⁰ but long-term impacts on fish stocks are not yet clear, and data on present levels of fishing have not been published. However, some reports suggest that productivity of migratory fish above the dam is well below original levels. It has been suggested that initial seeding of the reservoir by migratory species was poor, as the Yacyretá Dam was finished during a year of poor larval recruitment and at a time of year when migratory stocks were below the dam in feeding areas.⁴⁰¹

Effective fish passage could theoretically alleviate this problem. Preliminary information on the effectiveness of the fish elevators for fish passage that were installed on this dam indicates that 44% of the species

³⁹⁶ Quirós, 1993

³⁹⁷ Bechara et al., 1999; Terraes et al., 1999

³⁹⁸ Domitrovic et al., 1994; Bechara et al., 1996

³⁹⁹ Environmental Defense, 1999

⁴⁰⁰ Inter-American Development Bank, 1997

⁴⁰¹ Oldani, 1994; Oldani et al., 1992

registered in the tailrace were transferred at least to some extent (a total of about 252 tons or 1,767 million fish in 1995). The passage was used primarily by the small catfish Pimelodus maculatus (72%) and P. granulosus (12%),⁴⁰² although the dourado (S. maxillosus) and the curimbatá (P. lineatus) were also significant users.⁴⁰³ However, Oldani et al. (pers. comm.) suggest that the two elevators, operating at their current average efficiency of 50,000 fish/month, only transport one-fortieth of an estimated annual total of 12 million migrating fish that would normally pass this point in spring and early summer.

Entrapment of larval fish by pumps for irrigation projects was considered a problem in Santa Fé as early as 1952–1954, leading to regulations for appropriate screening. These pumps were killing an estimated 400 tons of juvenile fish annually. The issue was raised again in 1996, and is still currently being studied.⁴⁰⁴

The introduced species Cyprinus carpio was the most important in biomass in the experimental catches in the La Plata River, and its catch has been increasing in the Middle Paraná. Introduced species are also predicted to have effects on the fish in the Lower Paraná,⁴⁰⁵ though what these effects will be is not known. In particular, Bonetto (1998) feels that the fish Plagioscion squamosissimus (originally from Piauí) and P. scrofa will gradually invade the Lower Paraná Basin from the upper basin, facilitated by the submersion of the Sete Quedas by the Itaipu Reservoir, and the common carp is already a significant component of the Rio de la Plata fauna. In addition, the Asian freshwater mussel Limnoperna fortunei and freshwater clam Corbicula spp. were introduced to the Rio de la Plata (probably in the early 1990s and late 1980s, respectively), and are now rapidly invading the rivers of the Paraná-Paraguay Basin. These are having significant effects on hydroelectric and irrigation installations, but Bonetto (1998) suggests that they may also provide a substantial new source of food for fish and may thus have a beneficial effect on the ictiofauna in the near future. In fact, Leporinus species have recently been found to feed on Corbicula spp. extensively, to the point where mass mortalities result from intestinal blockages with Corbicula shells.⁴⁰⁶

⁴⁰² Convenio SEC YT, 1996

⁴⁰³ Oldani, 1998

⁴⁰⁴ Bonetto, 1998

⁴⁰⁵ Bonetto, 1998

⁴⁰⁶ A. Agostinho & J. Senharini, personal communication

Impacts in Paraguay

In Paraguay, water quality problems are restricted primarily to the area of Asunción, where human population, industrial and commercial activities are concentrated.

An international proposal to link the Atlantic with Pacific Ocean ports in Chile by a road through the Chaco could bring with it major environmental impacts, from road construction, the passage of hundreds of trucks daily, and from the arrival of new colonists.⁴⁰⁷

Although there is ample legislation in Paraguay protecting wetlands and the environment, many feel that widespread disregard has led, among other consequences, to illegal transfers of ecological reserves (Rio Negro National Park) to private individuals, and to destructive clearing and burning of land.⁴⁰⁸

MANAGEMENT AND MITIGATION

Legislation: Argentina, Paraguay and Bolivia

Legislation: Argentina

Fisheries are under provincial jurisdiction in Argentina, with no national legislation. Each province sets its own regulations, which regulate licensing, fishing areas and seasons, size limits, and species-specific restrictions. Sport fishing reserves are common to many of the provinces in the Paraná Basin,⁴⁰⁹ as are restrictions on some species such as the pacu (P. mesopotamicus), jaú/manguruyú (P. luetkeni), and dourado (S. maxillosus). For example, the Entre Lagos province has an extensive set of fishery regulations for both commercial and sport fisheries, prohibiting all fisheries and transport of pacu and manguruyú, establishing sport fishing reserves and areas of no fishing, regulating fishing seasons for dorado and sábalo, and regulating gear, minimum fish size and catch limits.⁴¹⁰

⁴⁰⁷ Carron, 2000

⁴⁰⁸ Carron, 2000

⁴⁰⁹ Espinach-Ros & Delfino, 1993

⁴¹⁰ www.entrerios.gov.ar/produccion/dpesc07.htm, www.portalbioceanico.com/er_turismo global_inventario_superestructura_docl01.htm

Legislation: Paraguay

Law no. 799/96, established in 1996, regulates fisheries in Paraguay.⁴¹¹ This law defines subsistence, commercial, sport, and scientific fisheries, as well as aquaculture, and regulates licensing, fishing gear, size limits, fishing reserves (e.g. nets are prohibited in river mouths and lagoon openings and long lines are prohibited in canchadas – stretches of rivers cleaned of obstacles by fishing co-operatives for net fishing), transport and handling of fish and fisheries products, and the introduction of non-native fish species. The law also mandates the annual determination of fishing seasons, and permits species restrictions.

Legislation: Bolivia

The 1975 Bolivian law no. 12301 regulates Wildlife, National Parks, Hunting and Fishing.⁴¹² Implementation of the law has been varied,⁴¹³ initially under the auspices of the Department of Fisheries Development created in 1975, and then under the Fisheries Development Centre (CDP) established in 1984. The law was supplemented by a variety of regulations, most substantially in 1990 with a Fisheries and Aquaculture Regulation.⁴¹⁴ The law defines subsistence, commercial, sport, and scientific fisheries, regulates the importation and introduction of non-native aquatic organisms, and permits the concession of aquatic bodies to private use, but mandates that each productive water body have its individually designed detailed fisheries regulation.

Legislation: Brazil

In the Brazilian Constitution of 1988 a specific chapter on the environment deals with the common use of natural resources essential for a healthy quality of life, and outlines the duty of the common people and the government to protect and preserve the environment for future generations. The chapter deals with the protection of fauna and prohibits uses that place the ecology at risk or cause species extinction. In this light, migratory fishes are protected significantly in the national legislation.

⁴¹¹ www.geocities.com/derechopy/reglamentopesca.txt

⁴¹² www.elwa.org/resources/printable.asp?id=1233

⁴¹³ Palin, 1999

⁴¹⁴ Palin, 1999

Any activity that can cause significant environmental degradation is subject to environmental impact assessment, which needs to be communicated to all that are interested or can be affected. The Brazilian Constitution states that both federal and state governments have the right to legislate concurrently on forests, hunting, fishing, fauna, nature conservation, environmental protection and pollution control, with the most restrictive legislation taking priority. Based on this article, states such as Mato Grosso do Sul and Mato Grosso have developed their own environmental legislation related to fishing. Each fisherman that goes to these states requires a state permit, the income from which is used in Mato Grosso do Sul for enforcement by Polícia Militar Ambiental, and for the maintenance of the SCPESCA, the fish statistics collection system.

Law no. 6938, of August 1981, Política Nacional do Meio Ambiente (National Environmental Policy), includes as objectives not only social and economical development but also the preservation of environmental quality and ecological equilibrium, the maintenance and recovery of environmental resources for rational use, and the permanent availability of natural resources to preserve ecological equilibrium as life support. The law also places responsibility for recovery of damaged areas on those who pollute and promote degradation, and levies taxes on users that exploit natural resources for commercial purposes. One of the most important aspects of this law is the requirement for permits for activities that have high pollution potential, high natural resource use and a high potential for environmental degradation. The building of reservoirs for hydroelectric generation thus requires environmental impact assessments and mitigation measures to prevent the disappearance of migratory fishes, including ensuring their reproductive migration.

The maintenance of natural conditions in rivers is one of the biggest challenges for maintenance of river fish populations, particularly as it relates to riparian vegetation. In this respect, Law no. 4771 of the Forestry Code (September 1965) defines riparian vegetation as areas of “permanent preservation”, which means that they cannot be removed or destroyed. The width of riparian vegetation that cannot be removed varies with river width: the larger the river, the greater the band of riparian vegetation that must be preserved. This is of particular importance for fish that feed on

leaves, seeds or fruits from riparian vegetation. Unfortunately this law is largely ignored, and farmers continue to cut and burn to the river banks.

Law no. 8171 on Agricultural Policy (Política Agrícola), enacted in 1991, includes such objectives as protecting the environment, guaranteeing rational use, and stimulating recovery of natural resources. Some aspects that are particularly significant are the promotion of technologies for natural resource conservation, particularly for fauna (including fish) and flora. According to this Law, companies that build reservoirs or dams are responsible for any environmental effects and for the recovery of the natural resources in the watersheds. One article states that the government must implement programs that promote fish-rearing activities in order to increase food production and preservation of species.

Law no. 7679 (November 1988) defines fishing prohibition periods, minimum capture sizes, catch quotas, permissible gear, and fishing permits for natural fish populations. Another important recent law is the Lei das Águas (Water Law of 1997), whose geographic scope for implementation is the watershed. Each watershed will have a Water Commission that will discuss the competing water uses, aiming for the best results for the whole community. If the planning unit is the watershed, it is possible that gains in water management can be achieved, particularly for fisheries resources.

One of the most recent laws, the Law of Environmental Crimes, or the Law of Nature of 1998, defines environmental crimes and the punishment for each. For fish and fisheries, to fish in prohibited places or in prohibited periods, the punishment will be prison for one to three years, or a fine, or both. The same will happen to someone who captures protected species, harvests sizes smaller than permitted or in amounts greater than permitted, who uses prohibited gear or methods or who markets or processes fishes caught with prohibited gears or methods. If the fishing is done during the night, on holidays or Mondays, punishment can be increased by one third. However, community service, a temporary injunction of rights, partial or total suspension of activities, fines or in-house arrest can be substituted for prison terms. It is not considered a crime if the fishing is done for subsistence.

Under the Convention on Biological Diversity Brazil has prepared a manual for assigning an economic value to environmental resources.

Regulation of Fishing in the Pantanal

The Mato Grosso and Mato Grosso do Sul governments, concerned about migratory fish reduction and extinction, have banned the capture of migratory fish during the spawning period, which generally lasts from the first of November to the end of January. For Mato Grosso do Sul, this ban extends to the end of February in the river headwaters. Table 8 shows the minimum allowable capture size, for commercial and sport fishing, based on the size needed for reproduction. Size restrictions for L. friderici, L. obtusidens, S. borellii, H. platyrhynchos and S. lima have not yet been imposed.

The amount that each sport fisherman can capture on each trip to the Pantanal is 15 kg or one specimen in Mato Grosso do Sul State and 20 kg or one specimen in Mato Grosso State. In Mato Grosso State, each commercial fisherman can transport 100 kg/vehicle or 1000 kg if transporting for a fishermen’s association, independent of fish species.

In parts of the Negro River (Mato Grosso do Sul) the only fishing allowed is “catch and release”. The “catch and release” was extended to the Abobral, Perdido and Salobra rivers in 2000.

In Mato Grosso State, in addition to seasonal and geographical restrictions, it is a crime to fish with explosive or toxic substances, within 500 meters of sewer outfalls, or within 200 meters of rapids, waterfalls, or fish ladders.

Conservation of Wetlands in Brazil

Since 1993 Brazil has substantially updated environmental laws and institutions to meet its commitments under the Ramsar Convention on Wetlands⁴¹⁵, and now has a national environment policy aimed at the sustainable use of natural resources, including water resources. Five sites have been designated for the Ramsar List, covering 4,536,623 hectares, which is the fifth largest total area among Ramsar member states.⁴¹⁶

The Water Law of 1997 recognizes water basins as the basic unit for planning and implementation. Planning of a national strategy for wetlands is underway, based on several initiatives of the Ministry for the

⁴¹⁵ The Convention on Wetlands, signed in Ramsar, Iran, in 1971

⁴¹⁶ http://www.ramsar.org/about_five_parties.htm#braz

TABLE 8. Minimum capture sizes in Mato Grosso do Sul

Environment. The first stage is the setting up of a database on the geography of Brazilian wetlands. A national wetland strategy will be established through a resolution of the National Environmental Council (CONAMA) and the Brazilian Agency for Environment Protection (IBAMA). Environmental agencies in the federal states will be responsible for implementation.

In 1986, based on Brazil’s 1981 law for environmental impact assessment, which is applicable to all sectors, CONAMA made environmental impact assessments obligatory for activities that significantly affect wetlands. Programmes are being implemented to restore and rehabilitate wetlands, including the sustainable development of the Pantanal. Legislation also promotes participation of the private sector in the establishment and management of protected areas, many of which are private. Local communities and NGOs participate in the decision-making process through management committees, especially with regard to protected areas.

In Brazil, the Environmental Protection Agency maintains both broad scope programs, such as the one that created a national inventory of wetlands in 1988, and special programs, such as those designed for teaching the population the importance of protecting water and marine resources. One such program is the Movimento dos Cidadões por l’Agua Organization (Citizenship Organization for Water), which was created by the Ministry for the Environment in 1996. In addition, a national program of environmental education (PRONEA) provides formal and informal education. Focusing on identifying training needs at the sectoral level, Brazil has developed a training program specifically for wetlands.

As part of their National Reports and based on COP6 recommendations, ten Contracting Parties to the Ramsar Convention announced steps to include under-represented wetland types in the Ramsar List of protected sites. A feasibility study was begun on the listing of new sites in the Brazilian states of Alagoas, Bahia, Goias, Maranhão, Mato Grosso do Sul, Paraná, Pernambuco, Rio de Janeiro, Rio Grande do Sul.

Relevant Conservation Programs in Argentina and Trans-boundary Programs

Argentina joined the Ramsar Convention in 1992. Three sites were designated for the Ramsar List of Wetlands of International Importance, and two more were added in 1995, another in January 1997 and 5 more by 2002, making a total of eleven sites covering 2,669,589 hectares.⁴¹⁷

Argentina has a subregional training programme funded by the Wetlands for the Future Initiative, and is currently focusing on promoting changes in land use, for economic activities ranging from cattle grazing to tourism. Argentina is also preparing to list two new Ramsar sites as part of the commitment to include under-represented wetland types in the Ramsar List, and has been co-operating with Paraguay for the management of common watersheds and fishery resources. Other regional agreements include the Amazon Co-operation Treaty, the River Plate Basin Treaty and Mercosur.

According to the National Reports, Argentina is the only Contracting Party to all environmental conventions. Brazil, Colombia, and Uruguay are parties to some of these conventions: the Convention on Biological Diversity, the United Nations Framework Convention on Climate Change, the World Heritage Convention and the Convention on Migratory Species.

Argentina is also co-operating with Paraguay to manage joint fish resources and watersheds, while Argentina, Brazil, and Uruguay are co-operating in the preparation of joint projects on migratory species as management indicators for wetlands in the Southern Cone.

Mitigation of the Effects of Dams

The National University at Misiones, the National University of the Northeast, the National University at Asunción and CERIDE/CONICET

⁴¹⁷ http://www.ramsar.org/profiles_argentina.htm

carry out the Yacyreta power authority’s program for mitigation. Fish populations, migration, and adaptation to the artificial reservoir and the System of Fish Transfer have also been studied. Fish culture stations are being built to produce and stock species whose populations have declined because of the dam. To aid migration, two elevators have been built, one at each end of the dam. As the fish cross the dam they can be identified and quantified, and samples measured, weighed, and marked in order to learn the migratory patterns and other aspects of the populations. Predictive water-quality models are also being developed.

Along the Aña Cúa branch, where three mini-dams are planned, it is hoped to minimize the impact that a decrease in the water level at specific times in the year would generate. Nevertheless, the Yacyreta Dam remains controversial.

RECOMMENDATIONS FOR CONSERVATION AND RESEARCH

The biology of the migratory fishes in the basin discussed needs more study. Basic biological information is lacking for important species such as L. obtusidens, L. macrocephalus, L. friderici, S. borellii, B. microlepis, B. orbignyanus, P. luetkeni, S. lima, and H. platyrhynchos. The role of the great lakes of the Pantanal is still unclear: are they really nursery areas and feeding ground for both young and adult fishes? Interrelationships between migratory and sedentary fishes and how these fishes are organized on assemblage or community level should also be studied.

To understand what is happening to migratory fish stocks more statistical data needs to be collected in the entire basin including in Mato Grosso State, Paraguay and Argentina. Genetic studies, based on DNA, are fundamental for stock discrimination, conservation and management programs. It is highly desirable that countries of the Paraná-Paraguay River Basin have the same or similar legislation to protect migratory fishes. There is also a need for the collection and sharing of statistical data on fishing.

Development plans for hydroelectric reservoirs are another area of concern. If existing Brazilian environmental legislation is properly put into practice through increased enforcement efforts, environmental

degradation will probably be reduced and conditions for migratory fishes will be improved.

Finally, environmental education will improve perception of the importance of fish. Not only fishermen but also farmers and others in the highlands that cause environmental degradation and put at risk the survival of migratory fishes should be educated in the consequences of continued degradation.

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Silva, M. V. da. 1986. Mitos e verdades sobre a pesca no Pantanal Sul-Mato-Grossense. Campo Grande, FIPLAN-MS. 146 p.

Sverlij, S. B., and A. Espinach-Ros. 1986. El dorado, Salminus maxillosus (Pisces, Characiformes), en el rio de la Plata y rio Uruguay Inferior. Rev. Invest. Des. Pesq., 6:57–75.

Terraes, J. C., J. A. Bechara, J. P. Roux, C. Flores Quitana, H. A. Domitrovic, and S. Sánchez. 1999. Ciclos reproductivos del sábalo (Prochilodus lineatus) y de la sardina de río (Hemiodus orthonops) (Pisces, Characiformes) en el río Paraná aguas abajo de la represa de Yacyretá, Argentina. Rev. Ictiología, 7:91–104.

Tümpling, W. V., R. R. Wilken, and J. Elinax. 1995. Mercury contamination in the northern Pantanal region, Mato Grosso, Brazil. J. Geochem. Explor., 52:127–134.

Wells, P. G., and G. R. Daborn (eds.). 1997. The Río de la Plata: an environmental overview. An EcoPlata project background report. Dalhousie University, Halifax, Nova Scotia, 248 p.

4
MIGRATORY FISHES OF THE
Uruguay River

Evoy Zaniboni Filho

Departamento de Aqüicultura/CCA

Universidade Federal de Santa Catarina

Florianópolis, SC, Brazil

Uwe H. Schulz

Fish Ecology

Universidade do Vale do Rio dos Sinos (UNISINOS)

São Leopoldo, RS, Brazil

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TABLE OF CONTENTS CHAPTER 4

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CHARACTERISTICS OF THE BASIN

Geography

The Uruguay River rises in the Serra Geral Mountains as the Pelotas River, near the southern coast of Brazil, at an altitude of approximately 1,800 m. It runs inland along the southern border of Santa Catarina State (Figure 1) until it joins the Canoas River, which drains Central Santa Catarina State. Below this confluence with the Canoas the river is generally considered to become the Uruguay. Continuing along the border between Santa Catarina and Rio Grande do Sul states, the Uruguay flows 938 km to the mouth of the Peperi River.⁴¹⁸ From the Peperi River confluence the Uruguay flows south for 1,324 km, marking the borders between Brazil and Argentina,⁴¹⁹ and Uruguay and Argentina, until it meets the Paraná River to form the estuary of the Plata River, which flows into the Atlantic Ocean (Figure 1).

The watershed of the Uruguay lies between the temperate latitudes of 28^o10’ S and 37^o08’ S, with a total course of 2,262 km. For the purpose of this study the beginning of the Uruguay River is considered to be the confluence of the Canoas and the Pelotas rivers 1,816 km from the mouth.⁴²⁰

The Uruguay is one of three rivers that form the Plata watershed,⁴²¹ which has an area of 3.1 million km²; the other two rivers are the Paraná and Paraguay. Between the mouth of the Uruguay and the Atlantic Ocean lies an area of approximately 18,000 km² that includes the Rio de la Plata, a saline estuary whose depth varies between 4 and 18 m.⁴²²

The total area of the Uruguay watershed is approximately 365,000 km². One hundred and seventy-six thousand km² are in Brazilian territory

⁴¹⁸ Santa Catarina, 1997a

⁴¹⁹ ELETROSUL, 1979

⁴²⁰ Boschi, 1989

⁴²¹ OEA, 1969

⁴²² Boschi, 1989

(equivalent to 48% of the area of the watershed), 46,000 km² in Santa Catarina State, and 130,000 km² in Rio Grande do Sul State.⁴²³

Geology

The Uruguay is the youngest river of the Plata watershed.⁴²⁴ Its hydrographic basin rests upon the sedimentary and volcanic rocks that compose the Paraná Basin. Igneous extrusive rocks (in the form of lava beds) from the Serra Geral mountains, in the São Bento Range, predominate and cover Mesozoic and Neo-Paleozoic sedimentary rocks deposited in subhorizontal spills at depths varying from 300 to 1,000 m. Radiometric dating indicates that the principal volcanic activity took place in the Middle Lower Cretaceous, from 120 to 130 million years ago. The

FIGURE 1. The Uruguay River Basin showing hydroelectric plants⁴²⁵ and regions of greatest pollution (shaded in )

⁴²³ Santa Catarina, 1997b

⁴²⁴ Soldano, 1947

⁴²⁵ UHE = Usina Hidrelétrica

geotechtonic characteristics are associated with the two predominant lithological blocks of sedimentary rocks and basalt. The soil normally has a high clay content and, in general, has little depth.⁴²⁶

The river is a series of pools and rapids, formerly highlighted by the Augusto César Gorge (1,493 km from the mouth), just below the confluence with the Peixe River, which dropped 8 m in only 7 km.⁴²⁷ This gorge was flooded by the reservoir of the Itá Hydroelectric Dam, which began to fill in December 1999. The Yucumã (or Moconá) Falls, below the mouth of the Peperi River, marks a drop of 12 m through a diagonal crevice, forming rapids approximately 1,800 m long, the widest in South America. Below the mouth of the Quarai River, the former Salto Grande Falls (353 km from the mouth of the Uruguay) dropped 9 m in only 3 km⁴²⁸; these rapids were flooded in 1979 after construction of the Salto Grande Dam. The Yucumã Falls divide the Upper and Middle Uruguay, while the Salto Grande is considered the border between the Middle and Lower Uruguay (Figures 1 and 2).

FIGURE 2. Vertical profile of the Uruguay River, showing river sections and locations discussed in the text

⁴²⁶ ELETROSUL, 1981

⁴²⁷ ELETROSUL/CNEC, 1990

⁴²⁸ CARU, 1993

River Profile

As a result of its rather broken profile and abundance of rapids, the Uruguay is less navigable than the other rivers of the Plata Basin. Currently, after dredging stretches of the Lower Uruguay, a canal 7 m deep runs from the mouth to the port of Concepción del Uruguay (184 km). Commercial navigation with small boats extends 252 km up the river, and, except for at low water, boats with a draft of up to 2 m can reach the Salto region (390 km upriver).⁴²⁹

As suggested by the vertical profile (Figure 2), the different sections of the watershed have considerably different hydrological conditions. The upper river is steep, with an average drop of 1.76% and primarily fast water. The rocky terrain and the topography of the drainage basin result in considerable and sudden variations in flow. In the upper river the maximum average flow is 9,387 m³/s; the highest historic peak flow in the region exceeded 23,000 m³/s. Flooding occurs between June and October, although great annual variations in water level can be observed (Figure 3).

The Middle Uruguay, on the other hand, begins approximately 130 m above sea level and flows nearly 800 km with an average drop of only 0.16%, with some rapids. In the Lower Uruguay, the river runs nearly 350 km with a total drop of less than 1m.

In the lower basin, the average monthly variation in water level is less than 2 meters between dry periods and high water. In the upper and middle sections the combined average variation is approximately 10 m.

Hydrological conditions of the Lower Uruguay are strongly influenced by the Salto Grande Hydroelectric Dam. Historically the variation in the river level was small, dropping only 1.2 m during droughts. In spite of this, large floods exceeded 10 meters in height. Ports above Fray Bentos were for that reason built with two levels, to allow operation in times of drought and flood.⁴³⁰ Vast floodplains accompany the main river stem.

Water Quality

According to ELETROSUL/CNEC (1990) and the Administrative Commission for the Uruguay River, or Comissão Administradora do Rio

⁴²⁹ CENNAVE, 2000

⁴³⁰ CENNAVE, 2000

Uruguai (CARU, 1993), the water of the Uruguay has, on average, a low level of pollutants. However, near the large cities, contamination from untreated sewage, and, in the upper watershed, contamination by hog and poultry farming effluents, produce locally high levels of contamination. Dissolved oxygen is normally at near-saturation levels. The pH of the water is close to neutral, while electrical conductivity and alkalinity increase along the river (Table 1).

FIGURE 3. Multi-year mean of average, maximum and minimum monthly water levels of the Upper Uruguay River⁴³¹ and the Middle Uruguay River⁴³², showing representative water flow magnitudes⁴³³

⁴³¹ Water levels for Upper Uruguay River taken at Itá (1,529 km from the mouth), between 1940–1998.

⁴³² Water levels for Middle Uruguay River taken at Uruguaiana (580 km from the mouth), between 1931–1992.

⁴³³ DNAEE (www.dnaee.gov.br)

TABLE 1. Physico-chemical characteristics of the Uruguay River water⁴³⁴

In situations free of human impact, the low phytoplankton production of the Uruguay is due to a strong current, relatively low concentration of nutrients and high turbidity.⁴³⁵ The productivity of aquatic macrophyte communities is also quite low due to the scarcity of pools and the near-absence of marginal lagoons. The low primary production makes aquatic communities highly dependent on organic material originating on land, even more so than in other rivers of the Plata Basin.⁴³⁶

Social Aspects

Human occupation of the river basin

European colonization of the Uruguay River Basin began in the mid-sixteenth century, when Spanish and Portuguese settlers established small villages along the lower river and mixed with indigenous peoples. Difficulty navigating to the upper basin impeded colonization until 1620, when Jesuit priests led a migration of Guarani Indians south from the lands east of São Paulo.⁴³⁷ After 1633, Caboclos, an ethnic group that sprang from the mixing of indigenous people and Europeans, moved in. Their principal activities were subsistence agriculture, the cutting of yerba maté for tea, cattle-raising and transport. After 1894 incentified settlement began, intensifying after 1917 when the Brazilian government, with participation of the German and Italian governments, paid the travel expenses of European immigrants. Settlement was based on 20 to 30 hectare agricultural lots, which remain characteristic of the region.

⁴³⁴ ELETROSUL/CNEC, 1990; CARU, 1993

⁴³⁵ Quirós & Luchini, 1982

⁴³⁶ Di Persia & Neiff, 1986

⁴³⁷ ELETROSUL/CNEC, 1990

Agricultural development was accompanied by exploitation of the forests that covered the entire region. During the high water season, long rafts of cedars (Cedrella fissilis), angicos (Parapiptadenia rigida), grápias (Apuleia leiocarpa) and Brazilian pines (Araucaria angustifolia) were floated down the Uruguay to Argentina.⁴³⁸ In 1940 large sawmills were built, but after years of extraction the forests were depleted and the sawmills shifted to other regions.

After 1960, hog and poultry farms began to consolidate into large conglomerates, which have since dominated the Brazilian food market. Integrating with producers, these large agri-businesses have continued to stimulate the regional economy and have steadily increased productivity in hog- and poultry-raising.

In the Upper Uruguay agriculture revolves around soybeans, corn and black beans. In the Middle and Lower Uruguay, extensive cattle-raising and cultivation of soybean and rice prevail. Only fragments of the old forest remain along the boxed river valleys and on the steepest hillsides that people have been unable to occupy. In the Brazilian section of the river basin, primary and secondary vegetation cover nearly 17.5% of the land. Reforested areas, principally pines (Pinus elliottii), occupy another 3%. Compared with its original vegetation, with the exception of a few small remaining patches of primary forest nearly the entire region has been replanted to secondary vegetation, croplands and pasture.

The population density of the Uruguay River Basin is approximately 39 inhabitants per square kilometer. Nearly 45% reside in the rural areas.⁴³⁹ Despite the wealth and the stable economy, small economically depressed regions persist, mainly in the drainage basins of the Pelotas and Canoas rivers.

Habitats used by Migratory Fish

Upper and Middle Uruguay

The upper and middle sections of the Uruguay River occupy a fairly steep-walled valley with only a small floodplain that gradually flattens towards the headwaters. These characteristics directly influence the diversity and abundance of fish. The river bed is deeply channelled, broken up by waterfalls, rapids and narrows, and there are few islands or riparian

⁴³⁸ ELETROSUL/CNEC, 1990

⁴³⁹ Santa Catarina, 1997a ; Atlas Mirador, 1987

grasslands. The number of species found along the Uruguay River Basin probably surpasses the 150 species previously described.⁴⁴⁰ Data on fish productivity are not available, but the lack of floodplains in the Upper Uruguay suggests it is low.

Tributaries of the upper and middle section are normally short and broken by waterfalls. Migratory species and large fish are therefore generally restricted to the main river and to the lower section of the tributaries.

The migratory species present in the Lower Uruguay River normally rely on floodplain lakes for larval and juvenile rearing. As these lakes are absent from the steep valleys of the Upper and Middle Uruguay, the species appear to have adapted by using the mouths of tributaries as rearing areas. These areas of confluence take on lentic characteristics when the mainstem of the river floods, and backs up the waters of the smaller tributaries. Water transparency and temperatures tend to be significantly higher in these regions,⁴⁴¹ which leads to greater planktonic production and conditions favourable for larval and juvenile rearing.

Lower Uruguay

The Lower Uruguay resembles the Lower Paraná, which lies at the same latitude and a little farther west, and the fish species are practically the same. In both, species diversity and total fish biomass are high,⁴⁴² considering the sub-tropical climate. The high productivity may be due to a low profile and extensive floodplain, favouring the formation of shallow seasonal lakes and pools that accumulate nutrients.

Between the cities of Colón (236 km) and Fray Bentos (102 km) many large islands break up the Uruguay. 110 km from the mouth, at the outlet of the Gualeguaychú River, the islands disappear and the river widens substantially, reaching 8 to 12 km in breadth over a flat plain. A series of channels links the Uruguay and Paraná rivers in this stretch, with the Plata River strongly influencing the speed and direction of the currents in the Uruguay.⁴⁴³ During low water season, tidal influence is seen above the port of Paysandu, 204 km from the mouth.⁴⁴⁴ Since the construction

⁴⁴⁰ Di Persia & Neiff, 1986

⁴⁴¹ Zaniboni Filho et al., 2000

⁴⁴² Bertoletti, 1985

⁴⁴³ Sverlij et al., 1998

⁴⁴⁴ CENNAVE, 2000

of the hydroelectric dam at Salto Grande, these tidal effects have become more pronounced, particularly when water volumes released by the dam are reduced.

At Nueva Palmira, the Uruguay spills into the Rio de la Plata, a saline estuary covering approximately 18,000 km². The temperature of the Plata varies between 10 and 24^oC.⁴⁴⁵ Phytoplankton production is generally low and the ichtyofauna is composed primarily of sediment-eating, or iliophagic, fish.⁴⁴⁶ Euryhaline species predominate, and the presence of fresh-water species is low.⁴⁴⁷

MIGRATORY SPECIES AND MIGRATION PATTERNS

The fish community of the Uruguay is very similar to that of the Paraná River. Characiforms and Siluriforms predominate.⁴⁴⁸ In 1986, 150 species of fish were described for the Uruguay River Basin, including exotic, anadromic and estuarine fish.⁴⁴⁹ However, Hahn and Câmara (2000) identified 251 species in a brief bibliographic review of the Uruguay River.

Today, more than 100 species of fish are registered for the Upper Uruguay.⁴⁵⁰ The fish community of the Lower Uruguay is characterized by species of marine origin, such as Mugiliforms, Clupeiforms, flounders and rays. However, the species of the greatest biomass is the freshwater curimbatá (Prochilodus lineatus), a characid, which is fished intensely, sustaining industrial production of fishmeal and oil. As sampled by trawler, the curimbatá was found to be the most abundant species, occurring at a relative frequency of 23%. The voga (Schizodon nasutus) and the armoured catfish (Pterodoras granulosus) were second and third most abundant, at 4% and 3% respectively.⁴⁵¹ Other migratory species of commercial or recreational importance are the piava (Leporinus obtusidens), dourado (Salminus maxillosus) and Patí (Luciopimelodus pati).

⁴⁴⁵ Boschi, 1989

⁴⁴⁶ Quirós & Baigun, 1985

⁴⁴⁷ Boschi, 1989

⁴⁴⁸ Ringuelet, 1975

⁴⁴⁹ Di Persia & Neiff, 1986

⁴⁵⁰ Zaniboni Filho, et al., 1997

⁴⁵¹ Amestoy & Fabiano, 1992

Knowledge of the fish fauna of the Middle Uruguay is limited to the study by Bertoletti et al. (1989) of the stretch downstream from the Brazilian municipa