THE EFFECTS OF A HYDROELECTRIC DAM ON FISH IN AN AMAZONIAN RIVER By JOAO PAULO VIANA A DISSERTATION PRESENTED TO THE GRADUATE SCHOOL OF THE UNIVERSITY OF FLORIDA IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF DOCTOR OF PHILOSOPHY UNIVERSITY OF FLORIDA 1997 Copyright 1997 by Joao Paulo Viana To Rosa and Daniela. ACKNOWLEDGMENTS I would like to thank the members of my committee, Drs . Claire Schelske, Carole Mclvor, Carter Gilbert, Nigel Smith, Kent Redford, and Frank Chapman, for their support throughout the many years it took for the completion of this study. Their comments and editorial help on this dissertation are very much appreciated. I would like also to thank Drs. Geraldo Mendes dos Santos and Olaf Malm. Dr. Santos shared his Rondonian experience and experimental fishery data with me, whereas Dr. Malm's laboratory carried out the mercury determinations in fish for this study. Many institutions and people were involved in one way or another with this study since my first visit to Rondonia. The Tropical Conservation and Development Program and The Tinker Foundation supported a pilot study carried out in 1990. ELETRONORTE (Centrais Eletricas do Norte do Brasil S.A.) provided housing and laboratory facilities throughout the pilot study and during the two years that took to complete the field work. ELETRONORTE ' S personnel (Mr. Fernando Fonseca, Mr. Bruno Payolla, Mr. Fernando Bastos, Mr. Rubens Guilhardi, and Mr. Carlos Frabbris) helped in a variety of problems and left me free to concentrate on my work. Mrs. Francisco Pereira and Jose Ribamar de iv Oliveira (former director and former administrative director of the Secretaria do Desenvolvimento Ambiental do Estado de Rondonia - SEDAM, respectively) support tremendously facilitated the field work. IBAMA (Instituto Brasileiro do Meio Ambiente e dos Recursos Naturais Renovaveis) provided the permits that allowed me to sample, to transport fish, and to donate voucher specimens to the Florida Museum of Natural History fish collection. I will be always in debt to Delmo Pereira dos Santos, Augusto Felicio da Costa, Jonas Brandao Ares, Francisco Rodrigues dos Santos Filho, and Carlos Felicio da Costa (but specially to the first two) for their help with the field work, and for their patience and understanding of my bad temper. Jose Batista Gomes expertise in fixing condemned gill nets allowed me to always have enough sampling gear available to replace those damaged by caimans and piranhas . This study was supported by the World Wildlife Fund (WWF-US and WWF-Brazil) and Conservation International (CI) . Several members of these organizations, but specially Dr. Cleber Alho from WWF and Dr. Gustavo Fonseca from CI, were essential to assure an easy flow of the funds that supported the field work. I am very thankful to CNPq (Conselho Nacional de Desenvolvimento Cientifico e Tecnologico) that granted me a scholarship that supported my academic work. The friendship of Jay Malcolm, Justina Ray, Gilberto and Paulina Lunardi, Claudio and Suzana Padua, Frank Jordan, John Chick, among others, during the many years in Gainesville made life much enjoyable. v Penny Magee and Gay Biery-Hamilton introduced me to the social perspective of river regulation. A very special thanks to Ms. Martha Love, whose kindness and diligence helped tremendously to speed communication with my committee members while I was in Brazil, and to deal with the incredible amount of paperwork that a Ph.D. candidate at the University of Florida has to do in order to graduate. Without the moral and financial support (during the last stages of this work) of my mother, Maria Julia Viana, the completion of this work would have taken much longer. Finally, I would like to thank Rosa Lemos de Sa for her continuous stream of understanding and unending help. Rosa and our daughter, Daniela, had to live with my frequent absence during field work, and to stand the worst of my nature while writing this dissertation. I apologize for that. vi TABLE OF CONTENTS ACKNOWLEDGMENTS iv ABSTRACT X CHAPTERS 1 INTRODUCTION 1 Background 1 2 PHYSICAL AND CHEMICAL POST-DAM ALTERATIONS IN THE JAMARI RIVER 6 Introduction 6 Methods 7 Study Area 7 The Samuel Hydroelectric Dam 7 The Study Rivers 10 Site Selection and Sampling Scheme 11 Data Analysis 14 Results 15 Hydrological Regime of the Jamari, Candeias, and Jaci-Parana Rivers 15 Daily Water Level Variation 17 Physical Characteristics of the Study Rivers 19 Samuel Reservoir Profiles 21 Water Physico-chemical Parameters of the Jamari, Candeias, and Jaci-Parana Rivers 21 Discussion 27 The Lower Candeias River 29 Water Quality in the Jamari River 31 Temporal and Spatial Variation in Oxygen and Temperature .... 32 3 LARGE FISH RESPONSES TO THE REGULATION OF AN AMAZONIAN RIVER 35 Introduction 35 Methods 3 9 Study Area and Study Rivers 3 9 Fish and Environmental Sampling 40 Gill Net Sampling 44 Laboratory Work 45 Missing Data 46 Data Analysis 46 Comparison of Gill Net Samples from the Jamari River Before and After Dam Construction 46 Differences in Yield Among the Jamari, the Candeias, and the Jaci-Parana Rivers 50 Fish Assemblages Before and After the Samuel Dam 50 Results 54 General Characteristics of the Gill Net Surveys 60 Gill Net Yield of the Regulated Jamari River in Relation to Two Free- flowing Rivers 65 vii Comparison of Gill Net Samples from the Jamari River Before and After Dam Construction 69 The Fish Fauna of the Jamari River Before and After Regulation 75 River Fish Assemblages : Their Responses to Natural and Artificial Environmental Gradients 80 Discussion 89 The Jamari River Fish and the Physico-chemical Alterations Brought About by the Dam 91 The New Hydrograph of the Jamari River and Its Hypothesized Consequences 92 The Tucurui Dam and Its Tailwater Fisheries 9 6 Large Fish Assemblage Responses to the Regulation of the Jamari River 97 Fish Assemblage Responses to Natural and Artificial Gradients 101 Artificial Gradients and River Fish Assemblages 103 Perspectives for Large Fish in the Jamari River and Other Amazonian Rivers 108 4 SPATIAL RESPONSES OF SANDY BEACH FISH ASSEMBLAGES DOWNSTREAM FROM A HYDROELECTRIC DAM ON A TROPICAL RIVER 110 Introduction 110 Methods 113 Study Area 113 Sampling Sites 116 Data Analysis 119 Fish Species Distribution and Faunistic Composition Among Rivers 119 Spatial Responses of Habitat-use Groups of Sandy Beach Fish to River Regulation 120 Results 122 Fish Distribution Patterns Among the Study Rivers 127 Species Richness Patterns Among the Study Rivers 128 Spatial Responses of Habitat-use Groups to River Regulation . . . 129 Discussion 132 Life-history Traits and the Susceptibility of Amazonian Fish to River Regulation 133 Environmental Alterations in the Jamari and Candeias Rivers . . . 134 Hydrological Alterations 13 6 Responses of Habitat-use Groups to Hydrological Alterations . . . 137 Small Fish Responses to Regulation, Comparing Two Case- studies 137 Predation, Colonization, and Habitat-use Group Responses to the Regulation of the Jamari River 140 Colonization Success 143 Prospects for the Small Fish Fauna of the Jamari River 144 5 FISH MIGRATION, DAM CONSTRUCTION, AND MERCURY CONTAMINATION IN THE MADEIRA RIVER BASIN 147 Introduction 147 Material and Methods 149 Study Rivers 149 Fish Collection and Mercury Determination 150 Data Analysis 152 Comparisons of Mercury Concentrations in Fish from the Madeira River and Its Tributaries 152 viii Comparisons of Mercury Concentrations in Fish Species from the Hydroelectric-developed Jamari River and Two Free-flowing Rivers 153 Results 154 Comparisons of Mercury Concentrations in Fish from the Madeira River and Its Tributaries 156 Comparisons of Mercury Concentrations in Fish Species from the Hydroelectric-developed Jamari River and Two Free- flowing Rivers 156 Discussion 160 Mercury Sources, Fluxes, and Transport in the Madeira River Basin 162 Fish Migrations and Mercury Dispersal 163 Fish Migrations in the Madeira River 164 Fish Migrations Elsewhere in the Amazon and Its Implications for Mercury Dispersal 166 The Samuel Hydroelectric Dam and Mercury Concentrations in Fish from the Jamari River Downstream from the Dam 167 New Reservoirs and Mercury Levels in Fish Downstream from Dams 167 Dams, Fish, and Mercury in the Amazon 169 6 GENERAL CONCLUSIONS AND RECOMMENDATIONS 173 Introduction I73 The Jamari River as a Model 174 Management Strategies for an Amazonian Hydroelectric- developed River I76 Future Perspectives of Hydroelectric Development in the Amazon 180 APPENDIX A FISH SPECIES RECORDED IN THE JAMARI RIVER DRAINAGE IN SELECTED HABITATS LOCATED UPSTREAM (UP) AND DOWNSTREAM (DO) OF THE SAMUEL WATERFALLS BEFORE AND AFTER THE CONSTRUCTION OF THE SAMUEL HYDROELECTRIC DAM 182 APPENDIX B EDITED TWINSPAN OUTPUT SHOWING CODED ABUNDANCE VALUES FOR 71 FISH SPECIES CAPTURED DURING THE DRY SEASON IN THE JAMARI AND IN THE CANDEIAS RIVER 189 LIST OF REFERENCES 191 BIOGRAPHICAL SKETCH 206 ix Abstract of Dissertation Presented to the Graduate School of the University of Florida in Partial Fulfillment of the Requirements for the Degree of Doctor of Philosophy THE EFFECTS OF A HYDROELECTRIC DAM ON FISH IN AN AMAZONIAN RIVER By Joao Paulo Viana August, 1997 Chairperson: Dr. Claire L. Schelske Cochairperson: Dr. Carole C. Mclvor Major Department: Fisheries and Aquatic Sciences The fishes from the impounded (1988) Jamari River, Brazil, were studied in 1993-94 to investigate downstream effects of a dam. Gill net sampling, targeting channel -dwelling species of large adult size, showed that the Jamari yielded twice as much fish biomass (40 kg/gill net set/day) as two other free-flowing rivers. Compared with available pre-dam gill net surveys, the number of fish taken per day increased 2- to 4-fold. However, yield as total fish biomass was largely unchanged because the mean biomass of individual fish dropped by half after regulation. Herbivorous fishes of high commercial value decreased in importance after impoundment, whereas the occurrence of species of low commercial value increased. Earlier occurrence of floods after regulation may have decoupled fish production from the peak availability of plant resources produced in the flooded forests. Many fishes depend on these resources, which explains smaller size of fishes and the observed drop in importance of herbivorous species in post-dam gill net surveys. x Species richness of small adult fishes (< 10 cm standard length) sampled by seining on shallow sandy beaches was severely reduced downstream from the dam during the dry season. Richness and abundance of species with broad habitat requirements increased downstream from the dam, but benthic fishes showed no signs of recovery along a 40 km study reach. Increased water levels (one meter above normal) appear to have eliminated a structural barrier (depth) between small prey fishes and large predatory fishes, resulting in depressed richness and abundance of fishes of small adult size along the Jamari after regulation. Mercury levels in piscivorous fishes of commercial value from the Jamari and two other rivers were higher than recommended for human consumption (0.5 \lg/g wet weight) by Brazilian regulations. These rivers had no history of gold mining, and therefore were not contaminated by mercury originating in their catchments . Upstream migration of fish from the gold-mined, mercury-contaminated Madeira River is the most likely mechanism explaining the presence of mercury- tainted fish in the study rivers . xi CHAPTER 1 INTRODUCTION Background The expansion of the Amazon's hydroelectric capacity is considered by planners to be a key to the Brazilian economic development for the next 20 years (Serra 1989) . Currently, there are only five dams operating in the region: the 42 MW Coaracy-Nunes (Araguari River, Amapa) , the 30 MW Curua-Una Dam (Curua-Una River near Santarem, Para) , the 8,000 MW Tucurui Dam (Tocantins River near Belem, Para), the 250 MW Balbina Dam (Uatuma River near Manaus, Amazonas) , and the 216 MW Samuel Dam (near Porto Velho, Rondonia) . About 100 dams are planned for exploiting an estimated 100,000 MW of hydroelectric potential (Junk and Nunes de Mello 1987) . The documented environmental and social impacts of existing dams has been quite negative (e.g. problems with resettlement of and assistance to traditional populations, poor water quality and decrease in fishery resources downstream from the dam) (Barrow 1987, Odinetz-Collart 1987, Gribel 1990, Magee 1990, Merona 1990, Odinetz- Collart 1991) . Most of these studies dealt with the Tucurui Dam. Tucurui was the first dam in Amazonia to have an environmental impact assessment study made, but when this study was ordered, the project was well under way. Even if this dam was found to be environmentally inadequate., it would have been too late to stop the process. Tucurui was part of a regional development project. Its cheap hydropower was the key for the construction of an electrometalurgical 1 2 complex in Eastern Amazon based on the Carajas Mineral Reserve of Para (Monosowski 1990) . The other dams operating in the Amazon were built largely to meet local demand of isolated urban centers such as Manaus , Santarem, and Porto Velho, substituting or complementing the generation of electricity by expensive oil-fueled power plants. Soon, electricity demands of the populated and highly industrialized eastern and northeastern Brazil will be the driving force behind exploitation of hydroelectric resources of the Amazon (Barrow 1988) . Much has been learned about the environmental impact of dams in the Amazon, and much has been missed because post-dam monitoring programs, when effectively started, did not last long enough. Such was the case of the Tucurui Dam, where fish monitoring programs were discontinued two years after the dam was closed (Ribeiro et al . 1995). Fish monitoring programs were also short-lived in the case of the Samuel Dam, and focused largely on changes occurring in the reservoir. The short life span of these planned monitoring programs represented an irrecoverable loss of information that could otherwise provide important input for future dam projects. The present study will focus on the downstream effects of the Samuel hydroelectric dam on both economically important food fishes and on the structure of fish assemblages. It is not just an attempt to fill a gap in information on the downstream effects of an Amazonian dam. It intends to provide suggestions that could be useful to mitigate them. In order to understand the consequences of hydroelectric dams, we should look first at the physical and water quality alterations brought about by river regulation. Chapter 2 will deal with this aspect of the problem. 3 In river-f loodplain systems, the flood represents a key component for the maintenance of system's productivity (Welcomme 1979, Welcomme 1985, Junk et al . 1989). A major mistake is to consider that reduction or elimination of floods is a beneficial effect of river regulation in the Amazon (Barrow 1987, 1988). Floods are essential for the Amazonian biota, and traditional populations in the Amazon pace their lives on the rising and falling of water. As is their environment, Amazonian people are also flood-adapted. Much of the disruption observed by Magee (1990) in the production system and livelihood of traditional people living downstream from the Tucurui Dam can be traced back to the hydrological modifications imposed by the dam, and fish are a key component in this chain . Fish are the main protein source for traditional Amazonian populations (Shrimpton et al . 1979), and an important commodity in the regional economy (Smith 1981, Merona 1990) . The floods are essential for the maintenance of freshwater fisheries throughout the Amazon because most commercially important food fish reproduce during high water, and their fry depend largely on food sources found in seasonally inundated floodplains (Goulding 1980) . Dams likely block migration routes of some long-distance migratory catfish; these fish appear to spawn in the headwaters of the Amazon River but their young rear in the Amazon estuary (Barthem et al . 1991). Dams likely also impede movements of resident and migratory fish within smaller regulated rivers. However, the extirpation of the floods might be the worst possible effect that a dam can produce because it will impede the access of fish to the food resources that maintain fishery productivity found on seasonally inundated floodplains. If regulation does not extirpate the flood pulse, 4 then we might expect that the overall productivity of the river fisheries downstream from the dam would not be severely affected. If this is true, then future hydroelectric developments in the Amazon should incorporate in their projects provisions to maintain the flood pulse. Chapter 3 will focus on this issue. Chapter 3 will compare fishery yield of food fishes and fish assemblages of the Jamari River pre- and post-dam, and also between the post-dam Jamari and two free- flowing rivers. Chapter 4 will deal with an extremely diverse, yet forgotten group of fish: those that because of their small size (adults with standard length usually less than 10 cm) have no importance for commercial fisheries (even though many species of this group are valuable or potential ornamental species). Bain et al . (1988) showed that small-size fish are more sensitive to river regulation than large- size fish. Therefore, small Amazonian fish species might be much more affected by hydroelectric dams than large, commercially important fish species. Chapter 5 will address another very important and nearly untouched issue related to the effects of dams in the Amazon. This problem has been recently recognized as an important primary effect of river regulation: the remobilization of mercury in recently flooded reservoirs and its assimilation by fish (Rosemberg et al . 1995). In the Amazon, dam construction and operation assume another dimension. First, fish in the Amazon are extremely mobile creatures. Current models of fish movements, based largely on characoids of commercial importance (Goulding 1980, Ribeiro and Petrere 1990) , suggest considerable exchange of fish among rivers. And second, some areas of the Amazon are being contaminated by mercury used in uncontrolled gold prospecting (Malm et al . 1990, Lacerda and Salomons 1991, Malm et al . 1995) . Because fish move so much, they might function as vectors of mercury dispersal in the Amazon, resulting in mercury- tainted fish present in rivers that were never exposed to gold mining. Because mercury remobilized in reservoirs is exported to downstream reaches (Aula et al. 1995, Meuleman et al . 1995), fish found downstream from dams in tributaries of mercury-polluted rivers can have even higher levels of mercury. We have essentially a chain of events that will expand the problem of environmental contamination of mercury to a much larger area, and that will eventually affect the traditional fish-eating population of the Amazon, and its health. Chapter 6 will present the overall conclusions of this dissertation with suggestions on how to mitigate downstream effects of hydroelectric dams. CHAPTER 2 PHYSICAL AND CHEMICAL POST-DAM ALTERATIONS IN THE JAMARI RIVER Introduction The construction and operation of hydroelectric power plants produce major modifications in physical and chemical characteristics of lotic systems, which will in turn induce changes in the river biota. The magnitude of these physical and chemical alterations depends on several characteristics of the regulated river and its reservoir, and on dam design and use (Ward and Stanford 1979, Petts 1984). Historically, greater attention has been given to changes that happen with the creation of a reservoir and the transformation of formerly running waters into an artificial lake. Even though such alterations are dramatic, the focus of this chapter will be on downstream physical changes in the regulated river. Dam construction can be expected to produce important alterations downstream, including changes in flow regime, transport of suspended particles, channel morphology, water temperature, and chemical conditions (Craig and Temper 1987) . Fish and other aquatic organisms, in turn, can be expected to respond to changes in physical habitat characteristics and water quality (Vanicek et al . 1970, Trotzky and Gregory 1974, Saltveit et al . 1987, Bain et al . 1988, Kinsolving and Bain 1993). This chapter describes basic features of the physical and chemical environment of the regulated Jamari River and two free-flowing rivers. This information will be used in the following chapters as it relates to 6 7 observed responses of fish assemblages to environmental alterations and extremes brought about by hydroelectric dam construction and operation in a tropical riverine environment. Methods Study Area The Jamari, Candeias, and Jaci-Parana rivers are located in the state of Rondonia in the upper Amazon basin at northwestern Brazil (Figure 2-1) . Rondonia has a tropical climate, with well defined rainy (summer) and dry (winter) seasons. Mean monthly temperatures are approximately 26°C in Porto Velho (Figure 2-2) . Mean maximum monthly temperatures in the Samuel Dam area during July 1977 through June 1978 ranged from 31.0°C to 34.5°C (maximum 38.8°C in August 1977), whereas mean minimum monthly temperatures ranged from 18.5°C to 22.4°C (minimum 15.1°C in June 1978) ( ELETRONORTE/ SONDOTECNICA 1978). Annual precipitation in Rondonia reaches 2500 mm in some areas, of which 45 to 55% falls from January to March (Figure 2-3, Brasil 1985). Precipitation in the Samuel Dam area from 1976 to 1987 ranged from 2010 to 2950 mm (mean of 2250 mm), and monthly mean relative air humidity was 74.2 to 90.8% (ELETRONORTE 1993). The Samuel Hydroelectric Dam The Samuel Dam, located at 8°45' S and 63°25' W, was closed on 17 November 1988 and flooded an area of 560 km2. The reservoir stores 3.25 lan3 of water at a normal operational water level of 87.0 m above sea level (Figure 2-1, ELETRONORTE 1990, Tundisi et al . 1991). Only Figure 2-1: Jamari, Candeias, and Jaci-Parana rivers. Stippled areas indicate the location of studied sites. 9 Figure 2-2: Mean monthly temperature in Porto Velho, Rondonia during 1928-1975 (ELETRONORTE/SONDOT^CNICA 1977). Figure 2-3: Precipitation in Rondonia at the Samuel hydroelectric dam (ELETRONORTE 1994) . 10 three of the five planned turbines were operational during most of this study (a fourth turbine started operating in September 1994) . The reservoir is 10-20 km wide and 40-50 km long, and is contained by two earth dikes that are 36.5 km (right bank) and 19.0 km (left bank) long (ELETRONORTE 1990). These dikes raised the reservoir level, allowing a gain of hydraulic head and consequently a greater energy output by the dam (Cadman 1989) . Because of gentle relief in the area, the reservoir extends about 140 km upstream from the dam, but in the upper reaches it floods only a narrow belt along the right and left bank of the Jamari River (Figure 2-1) . Due to the highly seasonal rainfall in Rondonia, the reservoir shrinks significantly in area by the end of the dry season (Tundisi et al . 1991), reaching as low as 140 km2 at 80 m above sea level, its minimum operational level (ELETRONORTE 1990, Mozeto et al . 1990) . Water used in the turbines is withdrawn from a fixed depth in the reservoir (10 meters below the normal operational level) , and the retention time of the reservoir is estimated to be 110 days . The Study Rivers The Jamari and Jaci-Parana River are tributaries of the Madeira River, whereas the Candeias River joins the Jamari River approximately 40 river kilometers upstream from its confluence with the Madeira River (Figure 2-1) . During the high water season, typically from December to May, the Candeias and Madeira rivers are connected through a 10 m wide man-made channel that was opened early this century as a shortcut to the rubber estates that existed along the Candeias and Jamari rivers. Water flow in this channel depends on the relative water level of the Candeias and Madeira rivers. In May 1993 water from the Madeira River flowed into 11 the Candeias, whereas the floods of 19 94 caused the Candeias to flow into the Madeira River. The three river drainages are north-south oriented, with their headwaters located in the Pacaas-Novos Mountains (600 - 700 m above sea level) , on the western edge of the Precambrian Brazilian Shield. Their middle and lower courses lay along the slopes of the Brazilian Shield (80 to 200 m above sea level), which are characterized by a gentle relief formed by pre-Tertiary sediments interspersed by scattered hills (Klammer 1984, Brasil 1985, ELETRONORTE 1993). The Jamari River drains 15,280 km2 at the location of the Samuel Dam (ELETRONORTE 1990), whereas the drainage area of the Candeias and Jaci-Parana rivers at the study reaches was estimated in about 13,000 km2. Their slightly acidic, low conductivity waters (Table 2-1) place them among the Clearwater- type rivers of the Amazon, according to the classification of Sioli (1984). Tropical rainforest constitutes the predominant vegetation in Rond6nia and along all three drainages, growing on red-yellow latosoils and podzolic soils (Brasil 1985) . About 15% of the original vegetation in Rondonia has been cleared during the past 20 years as a result of both spontaneous and organized colonization (Stone et al . 1991). Deforestation has been particularly severe in the area delimited by the right (east) bank of the Candeias River and the left (west) bank of the Jamari River between 9.5° and 10° S and along a 70-90 km wide belt on each side of the BR-364 Highway (Skole and Tucker 1993 ) . Site Selection and Sampling Scheme Three spatially-distributed sampling sites were established in the Jamari River to measure the downstream effects of the Samuel Dam. These sites were spatially distributed because physical and chemical 12 Table 2-1: Physical and chemical parameters of the Jamari, Candeias, and Jaci-Parana River waters. Parameters Jamari River Candeias River jaci-rarana k. Temperature (°C) 27.6 ±1.6 (59) 28.7 ± 0.5 (i) LI .L X l.o (J) Secchi depth (m) 0.8 ±0.3 (58) 1.0 ± 0.2 (3) A O X A O /1 C\* U.5 x U.Z (15; Dissolved oxygen (mg/1) 6.90 + 0.51 (57) t A/( m n ai /i\ /.04 ± U.43 (J) 0.34 X 1 .U5 (13/1 pH 6.45 ± O./y (Do) J. 51 x U.4Z (ilj f. 11 x A on /1 491* O.Z1 X U.ZV yViL) Conducuvity (uS/cm) 19 ±4 (58) 1 A X A 1U ± 4 (j; 1/1 x 35 meters) and the second point was situated in the adjacent flooded vegetation (depth 20-25 meters, depending on the reservoir level) . A van Dorn bottle was employed to collect water samples . Data Analysis The hydrological surveys of the Jamari River performed by ELETRONORTE and its contractors provided information on the hydrological characteristics of the Jamari River prior to regulation (ELETRONORTE/ SONDOT^CNICA 1978, ELETRONORTE 1994) . Data from these surveys were used to generate the hydrograph of the Jamari River. These data were compared with that recorded during this study and also with data (mean monthly 15 river stage between 1990 and 1994) compiled from unpublished reports by the Department of Planning and Statistics of ELETRONORTE (CEON- ELETRONORTE) to document the changes induced by regulation of the Jamari River on its natural hydrological regime. Seasonal and temporal variation in water physico-chemical parameters of the Jamari and the other rivers were compared in order to evaluate possible modifications brought about by the dam. Results Hydrological Regime of the Jamari, Candeias, and Jaci-Parana Rivers The regulation of the Jamari River produced important alterations to its hydrograph (Figure 2-4) . Peak floods that pre-dam occurred in April were advanced by 1-2 months (February-March) after regulation and persisted longer. The natural, receding water phase of the hydrograph (that extended from April to June) was also advanced by 1 month, and the river remained in a semi-flooded state throughout the dry season (approximately 1 m above pre-dam levels during the study) . Water level peaked in February 1994 due to higher than average precipitation during this month (Figure 2-3) . Absolute variation in water level in the Candeias River reached more than 10 meters during this study (Figure 2-5) . According to local residents, the flood of 1994 was the highest in the past 15-20 years. The difference between minimum and maximum water level in the Jaci- Parana River and the Jamari River during the study was 6 and 8 m, respectively (Figures 2-4 and 2-5) . 16 J ASONDJ FMAMJ Month Figure 2-4: Annual water level variation in the Jamari River before and after regulation. Pre-regulation values based on data from July 1977 to June 1978, and from January 1982 to October 1988 (ELETRONORTE/ SONDOT^CNICA 1978, ELETRONORTE 1994) . Post-regulation values based on unpublished reports by ELETRONORTE ' S Department of Planning and Statistics (CEON) and this study (error bars = SD) . 17 Month Figure 2-5: Water level variation in the Candeias and Jaci-Parana rivers during this study. Daily Water Level Variation The daily amplitude of water level in the Jamari River was much higher than that of the Candeias and Jaci-Parana rivers (Figure 2-6) . Daily water level variation in the Jamari River was a function of electricity demand, which increased during the evening and decreased during the morning and afternoon hours. Besides this daily variation, there was also a weekly cycle associated with reduced demand of electricity during weekends, when most businesses and public offices were closed (pers . observation). 18 August 1993 November E "53 > o i— o "co (D > 'is o rr I I I I 16 -f 12 - 8 - 4 - 0 - -4 - -8 4 I I I I 8 - -4 - -8 - -12 -16 -I 0 - I I I I Jamari River February 1994 May Mil Candeias River i i i i / JU. 5*1 i i n i i i i 180 612 I I I I 180 612 August November I I I I I I I I Jaci-Parana River TXT MM' 'MM MM 180 612 180 612 180 612 MM MM \ MM 180 612 Time of the day Figure 2-6: Daily water level variation in the Jamari, Candeias, and Jaci-Parana rivers from August 1993 to November 1994. Symbols correspond to the three sample sites on each river (circle, upstream-most site; square, mid site; and triangle, downstream-most site) . 19 Figure 2-6 also indicates that high water in the Jamari River caused partial impoundment of the Candeias River waters. This effect was noted in the field (pers . observation) and it is evident at the most downstream site of this river, where daily variation in water level reached higher amplitudes when compared with sites farther upstream (Figure 2-6) . As in the most downstream site of the Jamari River, daily water level variation in the most downstream site of the Candeias tended to peak at 0600 hours due to the distance that the flood wave has to travel from the dam to reach this area. This backwater effect apparently extended up to the mid site of the Candeias River (approximately 18 rkm upstream from its mouth in the Jamari River) , as seem during November 1993 (end of the dry season) when recorded water level variation nearly tracked that of the downstream-most site (Figure 2-6) . Daily water level variation in the Jaci-Parana River sites was generally less than in the other rivers. The largest of these variations were associated with episodic storms (pers. observation). Daily water- level variation at the downstream-most site was particularly high in May and November 1994, and may have been influenced by changes in water level in the Madeira River, which is only 20 rkm downstream from this site . Physical Characteristics of the Study Rivers Table 2-2 summarizes some physical characteristics of a representative reach of each of the sampling sites in August 1994. These rivers have similar drainage areas and water physico-chemical parameters at the study reaches (Table 2-1) , but differ with respect to several physical attributes (Table 2-2) . The Candeias River was deeper than the 20 Table 2-2: Physical characteristics of the sampling sites in the Jamari, Candeias, and Jaci-Parana rivers in August 1994 (Site 1, upstream-most site; Site 2, middle site; Site 3, downstream-most site). River /Site Width I'm) T T IUUJ \ H I J Mftan fipnth (m) ITlvlUI VJv VJ LU yill f Water velocity ( m/sec) River discharge fm"V^ecfi JalHall Ivl V CI 1 lMIL 1 on ou % 1 n 71 1 1 1 111 9S7 7 Site 3 107 2.5 0.66 178.5 Candeias River Site 1 81 4.1 0.37 122.2 Site 2 80 4.5 0.30 109.5 Site 3 62 4.4 0.34 93.5 Jaci-Parana R. Site 1 74 1.1 0.53 44.8 Site 2 66 1.2 0.56 46.3 Site 3 101 1.4 0.68 93.5 other two rivers . The Jamari River tended to have greater discharges when compared with the Candeias and Jaci-Parana rivers. The range of estimated discharges for the Jamari River sites fell within the expected range associated with the operation of the dam (water levels between 53.5 and 54.3 m above sea level recorded during the dry season months of 1993 and 1994 correspond to discharges of 170-240 m3/sec, pers . observation) . In the case of the Candeias River, there was a reduction in the river discharge from the most upstream to the most downstream site, in accordance with the above mentioned backwater effect of the Jamari River. Differences in discharge between Site 3 of the Jaci-Parana River and the other two sites were a consequence of the presence of two major tributaries (Branco and Sao Francisco rivers) between Site 2 and Site 3 (Figure 2-1) . Even though creeks and streams were also present along the study reaches of the Jamari and Candeias rivers, they were few in number and very small. Their contribution to the above river discharge estimates and differences were most likely negligible. 21 Samuel Reservoir Profiles Vertical physical-chemical profiles of the Samuel Reservoir are shown in Figure 2-7. The profiles from Point 1 (former river channel) and Point 2 (flooded vegetation) were very similar, and will be reported together. Differences between surface and bottom water temperatures varied from 3°C to 6°C depending on the season. The lowest and highest recorded temperatures were 25.4°C and 33.3°C, respectively. Hypoxic conditions prevailed during most of the year at depths below 10 m except for March 1994 (rainy season) . The increase in dissolved oxygen at depths greater than 10 m and the almost uniform depth distribution of temperature, pH, and conductivity during this month indicate that mixing had occurred (Figure 2-7) . Water Physico-chemical Parameters of the Jamari, Candeias, and Jaci- Parana Rivers Figures 2-8 to 2-11 show variation in dissolved oxygen, temperature, pH, and conductivity at the Jamari, Candeias, and Jaci- Parana sampling sites between August 1993 and November 1994. Dissolved oxygen at sampling sites on the regulated Jamari River showed highest variation when compared with the non-regulated rivers . Oxygen concentration at the site closest to the dam ranged from saturated in February 1994 (rainy season) to hypoxic during the dry season months. Such extreme conditions gradually ameliorated with increasing distance from the dam. Seasonal variation in dissolved oxygen and water temperature for the Jamari River followed a pattern opposite to that recorded in the 22 26 28 30 32 0 2 4 6 8 0 30 60 90 6.0 6.3 6.6 6.9 12 18 24 30 36 Temperature(°C) D.O. (mg/l) % Saturation pH Conduct. (uS/cm) Figure 2-7: Vertical profiles at two adjacent points in the Samuel Reservoir (S = Secchi depth, RL = Reservoir level) . Point 1 (filled circle) located approximately 5 km upstream from the dam, over the former river channel. Point 2 (open square) located about 200 m from Point 1, over drowned vegetation. unregulated Candeias and Jaci-Parana rivers, where lowest oxygen concentrations and water temperatures were recorded during February 1994, the peak of the rainy season (Figures 2-8 and 2-9) . Seasonal 23 8 7 6 5 4 3 2 1 E 0 fi Q) 0 >> 5 O 4 "O 3 _> 2 ° 1 CO 8 7 6 5 4 3 2 1 Jamari River Site 1 - 8 - 7 - — i — i — i — i — r Candeias River Site 2 - "i i i i r Site 3 Site 1 - i — i — i — i — i — r Jaci-Paran£ River Site 2 - i — i — r i — i — i — r Site 3 Site 1 i — i — i — i — i — r A93 N F94 M A N Site 2 — i — i — i — i — r A93 N F94 M A N Site 3 i — i — i — i — i — r A93 N F94 M A N Month Figure 2-8: Seasonal variation in dissolved oxygen at sampling sites (Site 1 = upstream site, Site 2 = mid site, and Site 3 = downstream-most site) of the Jamari, Candeias, and Jaci-Parana rivers from August 1993 to November 1994 (A = August, N = November, F = February, M = May) . Most means based on 4 readings taken every 6 hours, from 1800 to 1200 hours of the following day. 24 Jamari River Jaci-Parana River A93 N F94 M A N A93 N F94 M A N A93 N F94 M A N Month Figure 2-9: Seasonal variation in water temperature at sampling sites (Site 1 = upstream site, Site 2 = mid site, and Site 3 = downstream-most site) of the Jamari, Candeias, and Jaci-Parana rivers from August 1993 to November 1994 (A = August, N = November, F = February, M = May) . Most means based on 4 readings taken every 6 hours, from 1800 to 1200 hours of the following day. 25 Jamari River Site 1 n i i i r Candeias River Site 2 "i — i — r Site 3 t — i — i — i — i — r Site 2 ~i — i — i — r Jaci-Parana River i — i — i — i — r A93 N F94 M Site 2 l — i — i — i — r A93 N F94 M A N Site 3 1 i r A93 N F94 M A N Month Figure 2-10: Seasonal variation in pH at sampling sites (Site 1 = upstream site, Site 2 = mid site, and Site 3 = downstream-most site) of the Jamari, Candeias, and Jaci-Parana rivers from August 19 93 to November 1994 (A = August, . N = November, F = February, M = May) . Most means based on 4 readings taken every 6 hours, from 1800 to 12 00 hours of the following day. 26 24 E _o CO > o ~U c o O Jamari River Site 1 12 10 - 8 - 6 - 4 2 n — i — i — r Candeias River Site 2 ~\ — i — r Site 3 t — i — i — i — i — r Site 1 Site 2 12 i — i — i — i — i — r Jaci-Parana River i — i — i — r Site 3 l i i i r 10 - 8 - 6 - 4 - 2 Site 1 — i — i — i — i — r A93 N F94 M A N Site 2 — i — i — i — r A93 N F94 M A Site 3 i — i — i — i — r A93 N F94 M A N Month Figure 2-11: Seasonal variation in conductivity at sampling sites (Site 1 = upstream site, Site 2 = mid site, and Site 3 = downstream-most site) of the Jamari, Candeias, and Jaci-Parana rivers from August 1993 to November 1994 (A = August, N = November, F = February, M = May) . Most means based on 4 readings taken every 6 hours, from 1800 to 1200 hours of the following day. 27 variation in pH and conductivity were similar between and within rivers (Figures 2-10 and 2-11) . However, greatest pH and conductivity- amplitudes were recorded at the site closest to the dam in the Jamari River, tending to gradually decrease downstream (from Site 1 to Site 3) . pH values were similar for the three rivers, but water conductivity was greatest in the Jamari (13 to 22 us/cm) , intermediate in the Jaci-Parana (7 to 11 pS/cm) , and lowest in the Candeias River (5 to 7 (iS/cm) . Water transparency in the Jamari River was higher than in the other two rivers, Secchi depth reaching up to 3 m in May 1994 (Figure 2- 12) . Transparency in the Candeias River was higher than in the Jaci- Parana River during the dry season and lower during the rainy season months, a pattern possibly associated with greater soil erosion in the Candeias drainage due to extensive land clearing within its basin (pers. observation) . Discussion Whenever dams are built, the hydrological regime of the regulated river is altered. The degree of alteration depends upon several features such as reservoir storage capacity, inflows and outflows, and reservoir use. The erosive power of the sediment-free water released by a dam, the altered flow regime, and the daily and weekly variation in water level associated with peak demands in electricity contribute to produce major rearrangements in the structure of the river channel downstream from hydroelectric dams (Guy 1980, Petts 1984, Ward and Stanford 1987) . Regulation of the Jamari River led to increased river flow during the dry season months (August to October, winter/spring) , during which river discharge was maintained at 170-240 m3/sec, as opposed to the 28 E 3- Q. CD T3 z o o CD CO c 03 CD 2 - 1 - Jamari River Candeias River Jaci- Parana River I 1 1 1 1 1 — Aug.1993 Nov. Feb. 1994 May Aug. Nov. Month Figure 2-12: Seasonal variation in Secchi depth in the Jamari, Candeias, and Jaci-Parana rivers from August 1993 to November 1994. Means based on readings taken at three sampling sites. typical discharge of 60-95 m3/sec before impoundment. As a result, water levels were raised roughly 1 m above pre- impoundment levels. Shallow habitats such as sandy beaches and sandy banks, common features of the Jamari River downstream from the Samuel Dam site before impoundment (ELETRONORTE/SONDOTF,CNICA 1976) , are now only partially exposed during the dry season. Those beaches that emerge are exposed to the erosional power of the water, which is intensified due to greater discharges and to a continuous variation in water level . Some beaches that appeared in August (early in the dry season) were completely eroded by November (late dry season). Signs of landslides, due to river bank erosion, were 29 also present along the studied reach of the Jamari River, and were most frequently observed closer to the dam. Alteration in the timing of floods and a reduction in annual peak floods are also consequences of river regulation (Ward and Stanford 1987) . In the Jamari River, the intensity of the floods was not affected after regulation, but its timing was advanced by 1-2 months. So, compared with rivers such as the Colorado (Dolan et al . 1974, Turner and Karpiscak 1980) or the Murray (Baker and Wright 1978) , where the floods were largely controlled, the effects of the regulation of the Jamari River on its hydrograph were relatively mild. However, this study documented the condition of the river while the Samuel Dam was not fully operational. As pointed out by Ribeiro et al . (1995), the characteristics of a river while regulated by a semi-finished dam can be different from those that will prevail after the dam is completed. The Lower Candeias River The maintenance of above average discharges in the Jamari River during the dry season months also affected the downstream reaches of the Candeias River by backing up its waters. River discharge estimates carried out in August 1994, and daily water level variation patterns during the dry season months showed that this river might be affected at reaches as far as 18 rkm upstream from its confluence with the Jamari. The actual upstream limit of the back-up effect of the Jamari River cannot be delimited without information on the topography along the Candeias River, information which is not available. In addition, the upstream limit should vary with the hydrological stage of the rivers involved. Independently of its upstream limit, the back up of water flow 30 in the lower reaches of the Candeias River should produce effects similar to those described for the Jamari River, i.e., prevention of shallow habitats such as sandy beaches and sandy bars from being exposed to the same extent that they were before the Samuel Dam started operating. Furthermore, reduced water flow due to backed up waters in the lower reaches of the Candeias River could presumably interfere with the natural processes of sediment transport and deposition. Reduced water flow in regulated rivers causes the main river to loose competence to rework the debris transported by an unregulated tributary (Dolan et al . 1974, Petts 1984). In the case of the Candeias River, sedimentation is possibly happening along its lower course because its normal flow is being partially blocked by high flow in the Jamari River. So far, there are no evident signs of sedimentation, but morphological adjustments of the river channel are long-term processes (Petts 1984) . ELETRONORTE is planning the construction of a diversion system to transfer water from the Candeias River to the Samuel Reservoir to improve the generation capacity of the hydroelectric facility during the dry season. According to this plan, flow in the Candeias River during the dry season months will be as low as 12.5 m3/sec, corresponding to the lowest recorded monthly mean discharge of this river ( ELETRONORTE /SONDOTECNICA 1989) . Such a diversion project, if actually implemented, would intensify the backing up effect of the Jamari River and enhance sedimentation in the lower reaches of the Candeias River . 31 1 Water Quality in the Jamari River Water quality in the receiving river depends on the conditions in the reservoir, as well as design and operation of the dam. Vertical profiles of the Samuel Reservoir showed that it remains stratified most of the year with hypoxic conditions prevailing at depths below 10 meters. The Samuel Dam has fixed depth intakes for the turbines at about 10 meters below the normal operating level of 87 m above sea level. Consequently, the Jamari River received only hypoxic water taken from the deeper layers of the reservoir during half of the year. The relatively uniform depth distribution of dissolved oxygen, temperature, pH, and conductivity during the rainy season of 1994 indicate that water from different layers of the reservoir had mixed. Total or partial mixing of reservoirs with hypolimnetic release can improve the oxygen concentration in the receiving river (Petts 1984) . Such improvement in the Jamari River water was offset by high discharges maintained in the spillways during this time of the year, which resulted in oxygen- saturated waters immediately downstream from the dam. Other reservoirs studied in southern Brazil (Froehlich et al . 1978, Arcifa et al . 1981) have unstable thermal stratification, with partial or complete mixing over the year. Holomixis, when detected in these reservoirs, was associated with the arrival of strong cold fronts (Froehlich et al . 1978) or occurred during cold months (Arcifa et al . 1981) . It is not possible to determine whether the Samuel Reservoir underwent complete or partial mixing during the rainy season of 19 94 giving the limited distribution of sampling points and reduced number of observations. Because shallow reservoirs like Samuel tend to have 32 unstable stratification (Petts 1984), it is possible that mixing occur throughout the year. Water circulation observed in the Samuel Reservoir was possibly triggered by increasing inflows and outflows during the rainy season, as reported for other tropical reservoirs (Sreenivasan 1964, Imevbore 1967). However, a partial vertical profile conducted in the reservoir in August 1993 (results not shown) , revealed the presence of water containing 2 mg/1 of oxygen at several depths between 5 and 3 0 meters, indicating that cold temperatures during this time of the year can also induce mixing in the reservoir thereby improving oxygen concentrations downstream from the dam. Temporal and Spatial Variation in Oxygen and Temperature The Samuel Dam altered the oxygen and temperature regime of the Jamari River. Such changes in oxygen concentration and water temperature were directly related to spillway operation. Typically, spillways were fully opened from January to March, releasing warmer, well-oxygenated to oxygen- saturated waters from the upper layers of the reservoir. By April, discharge through the spillways was gradually reduced until early June, when they were completely closed. Water flow in the Jamari River for the remainder of the year was maintained by colder, hypoxic water taken from the deeper layers of the reservoir, used to run the turbines. Extreme conditions in oxygen prevailed at the site closest to the dam, but tended to ameliorate as one progressed downstream. Changes in oxygen and temperature regime are common features of regulated rivers (Lehmkuhl 1978, Walker et al . 1978, King and Tyler 1982) . Modifications in the design and operation of dams might at least reduce extreme deviations from natural conditions (Petts 1984) . Selective withdrawal from different depths in a reservoir provides 33 flexibility for controlling the concentration of oxygen and temperature of the waters received by the regulated river (Cassidy and Dunn 1987). The Samuel Dam has a fixed depth withdrawal, and alteration of its original design may not be feasible. However, more dams are planned to be built in the Amazon region (Junk and Nunes de Mello 1987), and selective withdrawal can be incorporated into their design. In the case of the Samuel Dam, modification of its operational procedures, if feasible, may be the only option to ameliorate its downstream effects or the Jamari River. Ideally, the spillways of the Samuel Dam should remain partially open during the dry season in order to increase oxygen concentration in the water. In addition, the restitution of the Jamari to its former hydrograph would require reduced discharges during the dry season months. These operational alterations would result, however, in a significant reduction in energy output by the dam. A reduction in river discharge during the dry season months to levels as low as the ones that occurred before impoundment would require shutting down three or four of the five turbines during two or three months. Even though this represents a significant loss in electricity production by the dam, such loss might be partially compensated by scheduling the maintenance of the turbines for this time of the year. The implementation of this plan would require that Rond6nia had enough alternative sources of electricity to compensate for a reduced output by the Samuel Dam during the dry season. Unfortunately, this is not the case. Currently, the electrical generating capacity of the Samuel Dam (216 MW) can supply Rondonia's electricity demand (100 mean MW/month) . However, installed electrical generating capacity of oil-fueled power 34 plants (50-56 MW, Ms. Vania Ferreira, Department of Planning and Statistics, ELETRONORTE, pers . communication) is not enough to compensate for a drop in energy output by the Samuel Dam during the dry season. Eventually, the growth in electricity consumption in the state will require that more power plants be built, or that alternative options for electricity supply be identified. There are several options for Rondonia. First, there is the possibility of installing power plants fueled by the natural gas of the Urucu reserve in Amazonas . Secondly, the option of connecting Rondonia to the grid that supplies central Brazil is also being considered. Finally, there is the planned Ji-Parana Dam on the Machado River, which is in the feasibility study phase (Ms. Vania Ferreira, Department of Planning and Statistics, ELETRONORTE, pers. communication). Until Rondonia attains a surplus of electrical power, the implementation of changes in the operation of the Samuel Dam to return the Jamari River to conditions that approximate those that existed before regulation will have to wait. CHAPTER 3 LARGE FISH RESPONSES TO THE REGULATION OF AN AMAZONIAN RIVER Introduction The environmental record of hydroelectric development throughout the world is quite poor. Still, more and more dams are being planned, built, and put in operation because energy is essential for the prosperity of human society. In Brazil, a country that is rich in hydrological resources, hydropower accounts for over 90% of all electricity production (Petts 1990) . The largest eastern river basins in Brazil, which drain the most populated and industrialized portion of the country (the Parana and the Sao Francisco basin), have been transformed into a cascade of reservoirs with deleterious effects on the integrity of riverine systems. The Parana River alone has 25 large dams (installed capacity greater than 40,000 MW) (DNAE, National Department for Waters and Wastewaters, unpublished data) . One hundred dams have been proposed for the Amazon region in Brazil in order to exploit an estimated hydropower potential of approximately 100,000 MW (Junk and Nunes de Mello 1987) . By way of comparison, the Columbia River Power System in the Western USA that created tremendous impact upon salmonid migrations, consisted of 28 dams with a generating capacity of approximately 13,000 MW (Raymond 1988) . It is unlikely that all dams proposed for the Brazilian Amazon will be constructed (Leite and Bittencourt 1991), but many dams will eventually be installed. There is cause for concern 35 36 because we know relatively little about the details of what will happen to these modified systems and their biota. There are two theoretical perspectives on how lotic systems function. Vannote et al . (1980), using a geomorphological perspective, hypothesized that rivers can be viewed as a longitudinal continuum where the physical environment and its biotic components predictably adjust. In its original form, the River Continuum Concept (RCC) postulated, for example, shifts in aquatic invertebrate assemblage structure related to hypothesized responses of these groups to changes in organic matter processing and transport along the river continuum, and shifts in the relative importance of allochthonous vs. autochthonous production from headwater streams to midsize rivers. The RCC produced a wealth of studies aiming to verify its applicability, and while some studies found systems that conformed with its predictions, others did not (Allan 1995) . Its rationale applied to stream fish assemblages detected qualitative responses (e.g. shifts in assemblage composition along the continuum) consistent with RCC, but variability in the physical setting (flow regime) precluded quantitative predictions for these responses (Schlosser 1982) . Sedell et al . (1989) compared RCC predictions of carbon dynamics with the outcome of studies carried out in a large boreal and two large tropical rivers. They concluded that the RCC could be useful to predict carbon dynamics when dealing with constrained ( f loodplain-deprived) rivers, but was of little value when applied to river-f loodplain systems. Junk et al . (1989) pointed out that the RCC was based on observations from small temperate streams and could not be extrapolated to rivers in general. Additionally, these authors pointed out that the 37 RCC was limited in applicability by its unidirectional, upstream- downstream view of lotic systems. Based on studies carried out in nearly undisturbed South American and African rivers (e.g. Welcomme 1979, Goulding 1980, Welcomme 1985), Junk et al . (1989) developed the Flood Pulse Concept (FPC) , a theory emphasizing the importance of lateral interactions between the river channel and its floodplain. Junk et al . (1989) postulated that the flood pulse was the driving force controlling riverine biota in river-f loodplain systems. They further postulated that production of riverine biota is controlled by the degree of interaction between the river and its floodplain, and not by the transport (or leakage) of organic matter from upriver reaches as postulated by RCC. Because the geomorphological setting largely determines the degree of floodplain development in a given river or river reach, these two perspectives of how river systems function appear to be essentially complementary. We might expect that constrained rivers with poor floodplain development would conform to RCC predictions, lowland rivers with extensive floodplains would conform to FPC's, and rivers that cross different geomorphological settings would be of a hybrid nature (Sedell et al. 1989). The understanding of regulation effects upon river systems should use both RCC and FPC perspectives. Unquestionably, the most dramatic effect of dams is the elimination of annual floods (reviews by Welcomme 1979, Welcomme 1985). Flood regulation triggers a wide variety of modifications in the riverine biota. A regulated river where the flood pulse has been completely suppressed can be hypothesized as functioning as a constrained river, and very likely the River Continuum Concept could be useful for predicting, understanding, and proposing management 38 strategies to ameliorate impacts of river regulation. Alternatively, if hydroelectric development in a river system does not eliminate the flood pulse, then one might hypothesize that certain adjustments in the riverine biota would occur, but broad system parameters (e.g. fishery productivity, fish assemblage composition) would be relatively unchanged . This latter hypothesis was investigated in a tropical, recently impounded (1988) river whose dam was not fully operational, by sampling large riverine fish. This group of organisms represents an important natural resource for the Amazonian population and the understanding of how river regulation affects the composition and standing crop of the large fish component of the ichthyofauna has important socio-economical implications. In addition, the richness of freshwater fish species in the Amazon is unparalleled in any other area of the world, and the understanding of how regulation affects their diversity is badly needed in order to propose conservation measures. In terms of design, this is an unreplicated environmental field study. I have tried to overcome the limitation of lack of replication by using a design that incorporates spatially and temporally displaced sampling in the regulated and in two free-flowing rivers, as well as before vs. after comparisons (of temporally displaced samples) in the regulated river. Spatial and temporal displacement of samples contribute to increasing the strength of inferences and conclusions in unreplicated environmental field studies (Stewart-Oaten et al . 1986, Underwood 1994). The exploratory multivariate techniques of cluster analysis and detrended correspondence analysis were employed to understand patterns 39 in the responses of the assemblage of large riverine fishes to river regulation. Methods Study Area and Study Rivers This study was carried out in the state of Rondonia, northwestern Brazilian Amazon (Figure 2-1) . Rondonia has a tropical climate, characterized by dry summers and rainy winters. Annual precipitation in the state reaches 2,500 mm in some areas, and mean monthly temperatures are around 25.5°C (Brasil 1985). During the past two decades, colonization programs attracted thousands of settlers to this part of Brazil, causing a dramatic change in its landscape. Estimates for the amount of deforested area in Rondonia range from 10 to 15%, a significant proportion of it constituted by tropical rainforest (Stone et al. 1991, Skole and Tucker 1993). The field work for this study lasted from May 19 93 to November 1994, and consisted of regularly sampling three rivers: the Jamari, the Candeias, and the Jaci-Parana River. The Samuel hydroelectric dam (216 MW) construction was completed in 1988 on the Jamari River. However, only three of the five planned turbines were operating by May 1993. A fourth turbine started operating in the second half of 1994. The reservoir of the Samuel Dam flooded an area of 516 km2 of tropical rainforest, and dam operation produced major alterations in the Jamari River. First, river discharge remains above natural levels throughout the dry season due to the continuous electricity output by the dam. Secondly, the timing of peak floods occur two months earlier in relation 40 to the natural hydrological cycle. Thirdly, flood waters start to recede earlier in the year because spillway gates need to be closed to store water that will be used to operate the dam throughout the dry season. Finally, dissolved oxygen concentration in the water drops considerably by the early dry season, when the spillway gates are completely closed, and the only water that feeds the river is that used for producing electricity whose source is the deeper layers of the reservoir (Chapter 2) . The other two rivers are free-flowing rivers. The Candeias is a tributary of the Jamari River, joining it 41 river kilometers (rkm) downstream from the dam. The Jaci-Parana is a separate drainage adjacent to the Jamari-Candeias system (Figure 2-1) . Apart from the regulation of the Jamari River, the studied rivers are similar in terms of geological setting, water chemistry, and drainage area at the studied reaches. A complete description of the study area, the studied rivers, and of the physical and chemical alterations of the Jamari River is given in Chapter 2 . Fish and Environmental Sampling Fish and water physico-chemical parameters were sampled in the three rivers in May, August, and November of 1993; and in February, May, August, and November of 1994. These months were selected because they represent typical hydrological phases of the study rivers (May, receding water; August, low water; November, rising water; and February, flood) . Fish and environmental sampling took place at three sites on each river. Location of the sites took into consideration the availability of river reaches adequate for sampling with gill nets. These reaches were always 41 associated with meandering sections of the studied rivers, which create areas along the river bank that allow an adequate placement of gill nets. In the Jamari River the sampling sites were located 2, 21, and 33 rkm downstream from the dam. A similar spatial displacement of sites was followed in the other rivers, with two adjacent sites located 15-20 rkm apart from each other. The location of the sampling sites of the Jamari, Candeias, and Jaci-Parana rivers is shown in Figures 3-1 and 3-2. Figure 3-1: Location of the sampling sites of the Jamari and Candeias River. See Figure 2-1 for the position of this area within Rondonia. 42 Figure 3-2: Location of the sampling sites (PI to P3 ) of the Jaci-Parana River. See Figure 2-1 for the position of this area within Rondonia. Fish were sampled with a gill net set composed of 14 gill nets of five different mesh sizes. This method of experimental gill net sampling has been employed elsewhere in the Amazon (e.g. Ferreira et al . 1988, Lauzanne et al . 1990, Santos 1991, Ferreira 1993) and its adoption in this study allowed the comparison with records from pre-dam surveys (see below) . Note that such sets of gill nets are termed experimental in Brazil. Elsewhere (e.g. Canada, Bodaly et al . 1984b), experimental gill 43 net sampling consists of using gill nets assembled with panels of different mesh sizes. Throughout the present work I have chosen to omit the term experimental to avoid confusion with its usage in the English- language scientific literature where the term refers to a planned manipulation to the system in question. The number of nets in each mesh size (length between adjacent knots) was as follows: 15 mm (2 nets), 25 mm (2 nets), 35 mm (2 nets), 45 mm (4 nets), and 55 mm (4 nets). All gill nets were made of transparent nylon monofilament and were 2 m deep and 3 0 m long. Environmental sampling consisted of measuring selected water physico-chemical parameters (dissolved oxygen and temperature - Orion dissolved oxygen meter model 820, pH - Orion pH meter model 23 OA, conductivity - Fisher Scientific conductivity meter model NBS) ; and selected physical characteristics of the studied rivers (daily water level variation (to the nearest 0 . 5 cm using a graduated pole), Secchi depth (to the nearest 0.5 cm), water current (General Oceanics flow meter model 2030R) , and channel width (to the nearest meter using a graduated line) . Marks were also left in one site of the Candeias and one site of the Jaci-Parana River for measuring relative river stage throughout the duration of the study. River stage for the Jamari was obtained by reading the gauge located at the dam. Mean river depth was estimated in August of 1994 by measuring the depth (to the nearest cm using a graduated pole) every five meters in a cross-section of a representative reach in each sampling site. This information plus river stage measurements were used to back calculate mean river depth for all field seasons. Certain environmental parameters (dissolved oxygen - DO, temperature, pH, conductivity, and daily water level variation) were 44 measured every six hours, from 1800 to 1200 hours of the following day at each site and during each field season. The remaining physical parameters were measured during the morning of day 2 . Gill Net Sampling Gill net placement started around noon of day 1, and took from one to three and a half hours depending on the season and site. In February 1994 (flood) for example, gill net placement took much longer in most sites because it was extremely difficulty to find suitable spots to adequately fish with gill nets. Gill nets were always placed so that they would remain near the surface (to avoid tangling in submerged trees or protruding rocks) . The upriver end was always kept near or at the river edge, tied to branches or to wooden poles fixed to the bottom of the river. Gill net orientation normally followed a 15° to 3 0° angle with the river bank. The down river end was either left to float freely or tied to a pole, depending on local conditions, which in turn depended on the site and on the season. Small weights tied to the lead line had to be used occasionally to avoid the gill nets becoming twisted. Most difficulties in using gill nets occurred in the high water season (February 1994) in all places, and particularly when sampling the Jamari River. Variable discharges in this river throughout the day, associated with peaking and base electricity outputs by the dam, produced up to 60 cm variation in water level and changes in water current that regularly altered the characteristics of gill net sampling locations. At each site, each bank received an identical complement of gill nets (i.e. each bank had a gill net subset of identical mesh size composition) . Because it was very difficult to find spots suitable to accommodate gill nets along the river banks, the same general locations 45 at each site were repeatedly used for placing nets. These locations encompassed sections of the river that ranged from 1 to 2 rkm depending on the site. Gill nets were used until they had accumulated a loss of 15 to 2 0% of the netting area. The most common sources of damage in an estimated order of importance were: piranhas, caimans, very large fish, and river dolphins. Gill nets were inspected for fish every six hours, from 1800 hours of day 1 to 1200 hours of day 2. During each inspection captured fish were removed from the gill nets, placed in labeled plastic bags (date, time of day, and gill net identity) , and stored in Styrofoam coolers with ice, where they were kept throughout the field work. They were later transferred to freezers and kept deep-frozen until the field season ended (three to four weeks) . Laboratory Work Prior to examination, frozen fish were left to thaw at air temperature. Fish examination included: identification, measurement of standard length (SL) to the nearest mm and fresh weight to the nearest 0.1 g (using an electronic scale). Beginning in November of 1993, the degree of mutilation by opportunistic predators on gill-netted fish started to be recorded, and fish from which only parts of the body were recovered had convenient measurements taken (length of the head, body depth, etc.) depending on the recovered part of the body. Identical measurements were taken also from intact fish of the same species to estimate SL and fresh weight of mutilated individuals using regression equations. Identification of the fish was largely accomplished using a key compiled by Santos (1991), and complemented with additional sources (Gery 1977, Burgess 1989, Vari 1989a, Vari 1989b, Vari 1991, Vari 1992a, Vari 1992b, and Walsh 1990) . Voucher specimens of all species were 46 deposited in the fish collection of the National Institute for Research of the Amazon (INPA, Manaus, Brazil), and a partial collection (over 80 spp.) was deposited in the fish collection of the Florida Museum of Natural History, Gainesville, Florida, USA. Missing Data Some subsamples (i.e. plastic bags containing fish sampled with a given gill net in a given date and in a given time of the day) from November 1993 (5 out of 113 from the Jamari River, 7 out of 109 from the Candeias River, 3 out of 95 from the Jaci-Parana River) and February 1994 (15 out of 100 samples from the Jamari River, 4 out of 84 from the Candeias River, 1 out of 3 9 from the Jaci-Parana River) could not be located after completion of laboratory work. Apparently, these subsamples were removed without authorization from the freezers where they were stored. Measures were taken to increase storage security, and the problem was successfully corrected. Even though the disappearance of these subsamples represented an unrecoverable loss of information, it is unlikely that the loss of information significantly biased the outcome of this study. Data Analysis Comparison of Gill Net Samples from the Jamari River Before and After Dam Construction " " Fish species of commercial value were investigated in the Jamari River beginning in 1984, four years before the Samuel Dam started operating. The early phase of these studies was carried out by researchers of the National Institute for Research of the Amazon (INPA) lead by Dr. Geraldo Mendes dos Santos. In 1986 ELETRONORTE (the power 47 company that operates the Samuel Dam) transferred this work to a consultant company (SONDOTECNICA S.A.), which maintained most of the sampling sites surveyed by Dr. Santos. In addition, SONDOTECNICA expanded sampling to other areas of the Jamari River drainage, including the Candeias River (ELETRONORTE/ SONDOTECNICA 1987). The investigation of the Jamari River fish before dam construction was summarized by ELETRONORTE/ SONDOTECNICA (1987) and Santos (1991). Pre-dam data used in the present study came from 10 gill net surveys that span 1984 to 1988. Dr. Geraldo Mendes dos Santos (INPA, Manaus) provided semi-raw data on three of such surveys (total number and weight of fish per species per gill net mesh size per site per date) that will be used herein in most before and after comparisons. Differences in mesh size composition of gill net sets used by Dr. Santos and in this study (Table 3-1) necessitated care in comparisons. Two procedures were used. To avoid biases related to comparing yield records taken with gill net sets of different mesh size composition, the first procedure consisted of comparing yield (total number of fish, total number of fish species, and total weight per 24 hours of sampling) using only data from gill nets of identical mesh sizes (i.e. 15, 25, 35, and 45 mm mesh size, Table 3-1) . This conservative approach, however, resulted in the exclusion of most of the information contained in pre- and post-dam data sets. Therefore, in the second procedure yield before and after regulation was compared using all data gathered by pre-dam surveys (i.e. all records from the 10 gill nets that were used in these surveys), and records from 10 out of the 14 gill nets used in the present study. 48 Table 3-1: Mesh size composition used in gill net surveys before and after the regulation of the Jamari River, and in the comparison procedures adopted in this study (see text for explanation) Mesh size (mm) Before regulation Sample date After regulation June 1985 Sept. 1985 March 1986 This study Comparison procedure Procedure 1 Procedure 2 The selection of gill nets in the first procedure was carried out by randomly resampling the post-dam data set to keep one each of the 15, 25, 35, and 45 mm gill nets. The selection of gill nets in the second strategy was accomplished by randomly resampling and keeping two each of the 45 and 55 mm gill nets. Therefore, in the first procedure each post- dam sample (yield per 24 hours in a given site) was composed of catches from gill net sets of identical mesh size composition, whereas in the second procedure each sample consisted of records of 10 gill nets in sets of comparable mesh size composition (Table 3-1) . The process of selection of gill nets was repeated 100 times for each strategy, in order to obtain a better estimate of the yield per sampling site after regulation. Two sites located in the Jamari River channel (therefore similar to the ones in this study) were surveyed by Santos (1991) : MJ1 located 5 km upstream from the Samuel Waterfalls (that corresponds to the location 49 of the dam today) , and JJ located 5 km downstream from the Samuel Waterfalls (and therefore just 3 km downstream from site Jl of this study) . Because there were no differences in the mean number of fish (t=0.1858, DF=4, P=0.8616 considering 10 gill nets; or t=0.1733, DF=4 , P=0.8708 considering 4 gill nets), mean number of species (t=1.4194, DF=4, P=0.2288 considering 10 gill nets; or t=1.0233, DF=4, P=0.3 640 considering 4 gill nets), and mean fresh weight (t=-0.3630, DF=4, P=0.7350 considering 10 gill nets; or t=1.4625, DF=4, P=0.2174 considering 4 gill nets) between these sites, their data were pooled, resulting in six records of yield for the Jamari River channel before river regulation. These records were compared with six records from each of the three post-dam sampling sites using the average yield (±1 SD) of 100 randomly generated gill net sets (samples from May 1993 were not used in this comparison because they were performed using a different sampling protocol) . Even though only Jl (the upstream most sampling site of the Jamari River) corresponded to the general location of surveys carried out before river regulation, the inclusion of the other sites located farther downstream in the comparison allowed the evaluation of spatial variation in yield after regulation. Shifts in the importance of fish species in gill net surveys before and after construction of the Samuel Dam were evaluated by ranking them from highest to lowest order in yield (as weight and number), and also by comparing total catches, grouping fish within four categories of commercial value (1 = high commercial value, 2 = medium commercial value, 3 = low commercial value, and 4 = no commercial value) . The assignment of fish species to quality rank categories was based largely on the author's personal experience with the local fish 50 market because published sources for such information could not be located. The assignment of fish species to quality rank categories was greatly improved by Dr. Geraldo Mendes dos Santos's (INPA, Manaus) knowledge of Rondonian and Amazonian fish. KivS611065 ^ Yleld ^ ^ Jamari' the Candeias, and the Jaci-Parana Differences in yield (as number of fish, number of fish species, and fresh weight) per gill net set per 24 hours among rivers were tested using a balanced, fixed effects nested ANOVA (where sites were nested within rivers) and Tukey's multiple comparison procedure. Only records from the present study were used in this analysis. Fish abundance data were square-root transformed to meet the ANOVA assumption of homogeneity of variance. Fish Assemblages Before and After the Samuel Dam Fish assemblage responses to the regulation of the Jamari River were investigated using multivariate analysis techniques. Cluster analysis was employed to investigate the similarity of the fish fauna of the studied rivers and of the Jamari River before and after the Samuel Dam. Data on the presence/absence of species were used for clustering (weighed mean average method) sampling sites (records from the Jamari River before the Samuel Dam pooled as one site) using Jaccard's similarity coefficient. Presence/absence records from the fish fauna occurring in the Jamari River channel after regulation (all sites and dates of this study pooled) and records from the whole Jamari River drainage (Santos 1991, Appendix A) were also clustered using the same methodology in order to evaluate basin-wide patterns of faunistic similarity. 51 Detrended correspondence analysis (DCA) was used to identify patterns of river fish assemblage responses to natural (e.g. seasonal shifts in river fish assemblage structure between flood and low water season) and artificial physical gradients (e.g. river fish assemblage responses to regulation) . As a gradient analysis technique, DCA presupposes that species would respond to optimum and non-optimum conditions (i.e. natural and artificial environmental gradients) by temporal and spatial shifts in abundance and occurrence (ter Braak 1995) . DCA takes these responses at the assemblage level (a multidimensional data set consisting of species abundance records by sample) and constructs artificial variables in such a way that these new variables (or axes) will explain most of the variability contained in the data matrix, creating an artificial space where the samples will be positioned. Sample placement along these axes is a direct function of the internal structure of the data set (i.e. species composition and abundance) . Normally only the first two axes are useful for interpretation because they account for most of the variance contained in the data. Therefore, samples closer together in the space created by the artificial variables (the ordination diagram) would have similar assemblage structure whereas samples farther apart will have a less similar assemblage structure. The positioning of the samples along the axes can be interpreted by using either personal experience with the ecological setting, or by correlating sample scores (i.e. their position along the axes) with pertinent environmental data (Delucchi 1988, ter Braak 1995) . DCA was performed on both raw and relative abundance data, in a data matrix consisting of species (and species grouped into guilds) by 52 samples (i.e. a given site in a given date) . I used guild membership (species grouped on a basis of size, taxonomic affinity, and food habit) as a tool to aid in the interpretation of ordinations due to the large number of species involved. Three categories of size, based on average standard length (SL) , were defined: small (SL < 10.0 cm), medium (10.0 < SL < 20.0 cm), and large fish (SL > 20 cm) . Food habit assignment was largely based on Santos (1991) complemented with information available in Goulding (1980), and consisted of the following categories (piscivore, planktivore, omnivore, herbivore, and detritivore) . Taxonomic grouping was carried out at the ordinal level except for Perciformes and Clupeiformes where families were used. Thirty six size/taxa/food habit guilds (henceforth, STF guilds) could be defined considering the whole data set (Table 3-2) . Some species and guilds were excluded from the analysis to avoid distortions in the ordinations due to the interference that rare species or groups produce in DCA (ter Braak 1995) . The validity of using the guild-based ordination for the interpretation of the results was checked by correlating site scores between both ordinations (i.e. site scores of DCA Axis I of the species- based ordination with site scores of DCA Axis I of the STF guild-based ordination, etc.). If both axis correlated significantly (Spearman rank correlation) , the STF guild ordination was used as a tool to facilitate the interpretation of ordination results. Site scores were also correlated with 17 environmental variables (mean DO, mean temperature, mean pH, mean conductivity, mean water current, mean depth (and respective standard deviations), Secchi depth, channel width, total water level variation (the sum of the absolute value of water level 53 changes from 1800 hours of day 1 to 1200 hours of day 2), season, and when convenient, distance from the dam. Table 3-2: Size/taxa/f ood habit guilds (STF guilds) (and respective coded name) used in the detrended correspondence analysis (DCA) . o 1 r UU11Q VjullU cuuc Large rajiform omnivore LPOO Large clupeid piscivore t r*T p Medium engraulid omnivore MtUIN Small characiform piscivore i>CPi Small characiform omnivore SCON Small characiform detrihvore SCDE Medium characiform piscivore MCP1 Medium characiform omnivore MCON Medium characiform herbivore MCHE Medium characiform detritivore MCDE Large characiform herbivore Large characiform detritivore LCDE Large characiform planktivore t ranis' Large characiform piscivore LCPI Large characiform omnivore LCON Large gymnotiform piscivore LuPI Large gymnotiform omnivore LGON Small siluriform piscivore SSPI Small siluriform omnivore SSON Small siluriform detritivore SSDE Medium siluriform piscivore MSPI Medium siluriform omnivore MS ON Medium siluriform detritivore MSDE Large siluriform planktivore LSPK Large siluriform piscivore LSPI Large siluriform omnivore LSON Large siluriform detritivore LSDE Small cichlid omnivore SCIO Medium cichlid omnivore MCIO Large cichlid piscivore LCIP Large cichlid omnivore LCIO Large cichlid planktivore LCIK Large sciaenid piscivore LSCP Large sciaenid omnivore LSCO Large pleuronectiform piscivore LPLP Large beloniform omnivore LBEO 54 Results A total of 14,057 fish (1,824.7 kg), comprising 187 species (including four species -groups) , were captured during this study. Excluding the samples of May 1993, the total number of fish was 10,223 (1,487.5 kg) distributed among 183 species (including four species- groups) (Table 3-3) . These species groups consisted of certain fish species that during the early phase of the study were identified as one species {Geophagus cf. proximus, Pimelodus sp. 1, Sorubim lima, and Laemolyta varia) , but that with the progression of the study were considered as being composed of two (Geophagus, Sorubim and Laemolyta) or maybe more (Pimelodus) species. Because it was assumed that identification of these fishes was correct, many individuals captured during the early phase of this study were discarded, and after it became clear that they were in fact a mix of species, information about the identity of discarded fish from earlier field surveys could not be recovered. Therefore, Geophagus cf. proximus includes an undescribed Geophagus species of the Jamari and Candeias River; Sorubim lima consists of a "fat" species and a "thin" species that were found in all studied rivers, and Laemolyta varia includes an undescribed Anostomoides species from the Jaci-Parana River. Due to an extreme variability in characters used to identify Pimelodus found in members of Pimelodus sp. 1, it is not possible to define how many "species" are included in this group (maybe it is composed of just one, highly variable, species) . Because the actual status of Pimelodus sp. 1 is uncertain, and because similar grouping probably occurred in previous work carried out in the studied rivers, in the present study these species-groups will be treated as one valid individual taxa. 55 Table 3-3: Species identity with respective species code, STF guild assignment (guild code as in Table 3-2), quality rank (1 = high commercial value to 4 = no commercial value) , number of fish, and number of samples where the species appeared during gill net surveys of the Jamari, Candeias, and Jaci-Parana rivers. Classification Species Species STF Quality Jamari Candeias J.Parana code Guild rank n Samples n Samples n Sampli Rajiformes Potamotrygonidae Potamotrygon sp. Potamot LPOO 4 i i i i J 3 Clupeiformes Clupeidae Pellona caslelnaeana Pellonc LCLP 2 27 Q y 9 Pellona flavipinnis Pellonf LCLP 2 81 17 I j 1 Engraulidae Lycengraulis batesii Lyceng MEON 4 T1 17 • Characiformes Anostomidae Anostomoides laticeps Anostom LCON 2 5 2 7 7 ~ Laemolyta varia' Laemova LCON 2 146 j5 11 1 1 1 J ias 14 Laemolyta laeniata Laetaen MCON 4 29 4 1 1 8 5 Leporinus brurmeus Lepobru LCON 2 1 1 6 3 - Leporinus desmotes * Lepodes LCON 4 3 •3 J 1 1 Leporinus fasciatus Lepofas LCON 2 68 14 7JI Q c> 14 Leporinus friderici Lepofri LCON 2 50 jj 1 3 7 jy 14 Leporinus trifasciatus Lepotri LCON 2 1 1 L. cf. cylindriformis Lepokla MCON 2 18 O 1 7 J / / 13 7 Pseudanos gracilis Pseudgr MCON 4 1 ] 1 1 Pseudanos trimaculatus * Pseudtr MCON 4 2 7 D 3 Rhytiodus argenteofuscus Rhytioa LCHE 2 1 ] 4 1 7 6 Rhytiodus microlepis ** Rhytiom LCHE 2 1 1 1 Rhytiodus sp. 1 Rhytisp LCHE 2 9 5 l fi I U 6 Schizodon fasciatum Schizof LCHE 2 26 o o 0 0 2 2 Characidae Acestrorhynchinae Acestrorhynchus falcirostris Acesfar LCPI 4 13 in 1 4 4 Acestrorhynchus heterolepis Aceshet LCPI 4 4 i j Zo 10 73 11 Acestrorhynchus falcaltus AceslaJ MCPI 4 " 1 1 Acestrorhynchus microlepis Acesmic MCPI 4 1 1 20 6 165 14 Agoniatinae Agoniates anchovia Apnnial MCON 4 2 2 7 4 Bryconinae Brycon brevicauda Brybrev LCON 1 j 1 3 3 1 1 Brycon melanopterus Brymela LCON 1 14 8 20 5 1 1 Brycon pellegrini Brvpell MCON 1 1 1 Brycon pesu Brynesu SCON 1 5 3 24 7 - Chalceus macrolepidotus Chalceu MCON 3 201 13 148 13 186 12 Triportheus angulatus Tripoag MCON 2 165 9 124 7 3 2 Triportheus albus Tripoal SCON 2 1 1 Triportheus culler Tripocu LCPK 2 2 2 5 3 Triportheus elongatus Tripoel MCON 2 54 11 103 12 Triportheus rotundatus * Characinae Acestrocephalus sardina Acessar SCPI 4 17 11 Charax gibbosus Charax g SCPI 4 3 2 Roeboides affinis Roebaff SCPI 4 3 2 Roeboides myersi Roebmye LCPI 4 1 I Roeboides thumi Roebthu SCPI 4 11 8 Roestes molossus Roestmo MCPI 4 19 6 56 Table 3-3 — continued. Classification Species Species STF Quality Jamari Candeias J.Parana code GuUd rank n Sampl :s n Samples n Samples Rhaphiodontinae Hydrolycus pectoralis Hydrope LCPI 3 10 7 6 4 1 1 Hydrolycus scomberoides Hydrosc LCPI 3 41 12 32 1 1 33 11 Hydrolycus sp. 1 Hydrosp LCPI 3 1 2 6 7 5 ■ Rhaphiodon gibbus Rhaphig LCPI 3 2 2 6 5 8 6 Rhaphiodon vulpinus Rhaphiv LCPI 3 401 17 88 i -7 56 13 Stethaprioninae Poptella compressa Poptell SCON A 4 _ 0 3 Tetragonopterinae Astyanax cf. anterior Astyant SCON i 4 1 1 1 3 5 Bryconops albumoides Bryalbu MCON A 4 5 2 77 1 1 53 6 Bryconops caudomaculalus Brycaud SCON 4 - _ 1 1 Bryconops melanurus Brynuru SCON 4 _ _ 1 1 Ctenobrycon spilurus Ctenobr SCON 4 * _ 1 1 Moenkhausia comma Mocomma SCON 4 _ 9 4 M. cf. grandisquamis Mogrand SCON 4 _ 2 2 Moenkhausia lepidura Molepid SCON 4 _ m 39 9 Moenkhausia sp. 1 Mospl SCON 4 1 1 ■ Moenkhausia sp. 2 * . _ ■ Tetragonopterus chalceus Tetrago SCON 4 1 1 2 2 3 3 Chilodontidae Caenotropus labyrinthicus Caenotr SCON 4 4 2 44 1 15 4 Ctenoluciidae Boulengerella maculata Boulema LCPI 5 3 2 36 1 1 Boulengerella ocellatus Bouleoc LCPI 3 50 16 55 16 - Curimatidae Curimata cf. inomata Curimai MCDE 3 4 2 4 3 Curimata knerii Curimak LCDE 3 94 10 13 7 Curimata ocellata Curimao MCDE 3 _ 1 1 Curimata roseni * Cuiimar MCDE 3 _ 22 I 27 6 Potamorhina altamazonica Potamal LCDE 3 59 9 6 4 - Potamorhina latior Potamla LCDE 3 313 13 78 10 3 1 Psectrogaster curvhientris Psectrc MCDE 4 69 5 20 2 1 1 Psectrogaster essequibensis Psectre MCDE 4 3 3 _ 1 / 5 Psectrogaster rutiloides Psectir MCDE A 4 n 9 4 10 i _ Curimatella alburna Curmalb SCDE 4 - 8 7 CurimateUa meyeri Curmmey MCDE 4 1 1 . ■ - Cyphocharax leucostictus Cyphole SCDE 4 _ 6 1 J - Cyphocharax cf. notatus Cyphono SCDE 4 2 1 2 2 Steindachnerina dobula Steindd SCDE 4 _ 1 1 " - Steindachnerina fasciata Steindf SCDE 4 ■ _ 7 1 3 1 Steindachnerina sp. 1 Steispl SCDE 4 8 2 11 5 " - Steindachnerina sp. 2 Steisp2 SCDE 4 _ 1 1 3 2 Steindachnerina sp. 3 Steisp3 MCDE 4 _ . 1 1 Erythrinidae Hoplias malabaricus Hopliam LCPI 3 _ 2 2 7 5 Hemiodontidae Argonectes scapularis Argosca LCON 3 4 3 10 7 - Eigenmannina melanopogon Eigenma LCPK 3 61 6 33 6 46 5 Hemiodopsis argenteus Hemiarg LCDE 3 - - 77 8 Hemiodopsis immaculatus Hemiima LCDE 3 54 7 29 5 Hemiodopsis microlepis Hemimic LCDE 3 26 4 70 10 Hemiodopsis semitaeniatus Hemisem MCDE 3 2 1 Hemiodus unimaculatus Hemiuni MCDE 3 89 15 94 16 168 17 Hemiodidae sp. 1 He mis pi LCDE 3 1 1 Hemiodidae sp. 2 Hemisp2 LCDE 3 1 1 57 Table 3-3--continued. Classification Species Snppip^ STF Ollali tv Tamari Candeias J.Parana code Guild Fiink n X am T\\ i 2 s n Samples n Samples Prrvfi 1 IrvlnntiHnp Prochilodus cf. mo Prochib LCDE 2 52 14 9 6 6 3 Setruiprochilodus taeniurus Sematae 2 3 3 1 1 - - S. theraponura Semathe LCDE 2 62 15 26 7 - - Nptth c n 1 m iHsp .'LI 1 a.Sdlll 1 ] UaC Colossoma mucropomum * - - . Myleus pacu Myleupa MCHE 2 2 1 3 3 10 7 Myleus sp. 1 Myleus 1 MCHE 2 6 4 l 1 Myleus sp. 2 Myleusz MCHH 2 3 2 13 5 12 8 Myleus sp. 3 Myleus3 LCHE 2 - 16 6 Mylossoma cm re urn Myloaur MCHE 2 10 3 17 6 - - Mylossoma duriventre 1 (, ,| I Mylodur MCHE 2 280 14 87 13 - . Piaractus brachypomum Piaract LCHE 1 2 1 - 1 1 Serrasalmus aureus Serrasa LCON 2 1 1 ■ - 1 1 Serrassalmus eigenmanni Senase MCON 2 38 8 13 8 23 9 Serrassalmus hollandi Serrash LCON 2 ■ _ 1 1 - _ Serrassalmus elongatus Serrasl LCPI 2 6 4 ■ - - - Serrassalmus rhombeus Serrasr LCPI 2 59 15 30 11 105 16 Serrassalmus striolatus S err ass MCON 2 1 1 " - - _ Serrassalmus sp. 2 Serrsp2 MCON 2 16 8 4 3 9 5 Serrassalmus sp. 3 Serrsp3 LCON 2 7 3 - - 1 1 Gymn otiformes F 1 e c trnn h ori Hap Ciiecifupnurus eiecincus Electro LGPI 4 2 2 - - - Rhamnhichthvidap f\ iitiiiij' ru t in ny}> mormoroius Rhamphm LGON 4 1 1 - 3 2 S ternopy g id ae lit Ct nrirlit t mm r/tvtri c is 1*3 1 \jy* ii_ i« .1 i,u ft* f la) I r U Distoci LGON 4 - 1 1 r i (7/nm/7nni/i vies (vj?mi t-rigcn/rmrifuu vi rc&LerlS Eigenvi LGON 4 1 1 4 3 l\iUiUUUllCrUJyA irUACrlcll Rhabdot LGON 4 7 2 £ i 1 1 Tri form p c Ageneiosidae Ageneiosus brevifilis Ageneib LSPI 2 33 12 15 7 17 9 ngenclUAUA VtllerlLienTlebl Ageneis LSPI 2 1 1 26 2 A 0J/~l1riI C IJr/1M/li0MFf F f\gcnciu3U3 uLuycucTisis Ageneiu LSPI 2 7 4 10 4 - - Ageneiosus atronasus Ageneia MSPI 4 - 14 6 A OPYtPi fwti <■ \n ttsitti r fXgericiusus vimilus Ageneiv LSPI 4 ■ - 4 2 Ageneiosus sp. 3 Agensp3 MSPI 4 • ■ - 8 5 AtirhpninfpriHap Auchenipterus nuchalis /iut ncmpiencfimys Auchnuc LSON 4 1 10 5 10 3 thoracatus Auchtho SSON 4 9 6 27 11 1216 16 Centromochlus heckelii Centrom MSON 4 428 6 283 17 33 8 Par auchenipterus galeatus Paragal MSON 4 7 5 4 3 4 3 Tatia sp. 1 Tatial SSON 4 ■ - - - 2 2 L/\jl dUlUdt Amblydoras hancockii Amblydo SSON 4 - ■ 2 2 1 1 Doras sp. 1 Doras 1 SSON 4 - - 2 2 32 7 Hassar sp. 1 Hassar SSON 4 1 1 Hemidoras sp. Hemidor LCON 4 25 7 AA 9 Opsodoras humeralis Opsohum MSON 4 2 1 18 8 1 1 Opsodoras stubelii Opsostu MSON 4 20 9 Opsodoras trimaculatus * Opsolri SSON 4 25 9 Platydoras costatus * Pseudodoras niger Pseudni LSON 3 21 4 1 1 Hypophthalmidae Hypophthalmus edentatus Hypophe LSPK 2 12 6 6 4 58 Table 3-3 — continued. Species Species STF Quality lamari Candeias 1 Parana code Guild rank n Samples n Samples n Samples rJvnnTihthnlm tin m/iroinsitu v * i yyyjyiiimAimws runt JffnwMM riypopnt 2 1 1 2 2 - ■ Ancistrus sp. 2 Ancist2 4 - - - 6 2 Cochliodoti sp Cochlio i enc 4 - - - - 36 16 TipmmAnnlichthyiK 1 1 r rr uifia i/ru ti ri in v acinpTixpTinii c Hemioac MI>Ub 4 2 1 15 6 18 5 Mypoptopoma gulare Hypopgu 4 - - - - 232 15 Hypoptopoma thoracatum T-Tvrw~w\tH I lj LX»fJUi SSDE 4 3 2 8 5 - Hypostomus sp. 1 Hvnncl 1 1 1 y l /u.> i j LSDE 3 - - - - 15 5 Hypostomus sp. 2 Hvnrwt? LSDE 4 11 6 27 10 - * Lasiancistrus scolymus T acic/v» MSDE 4 - - - - 5 3 Leporacanthicus gcilaxias Legal ax 4 - - 1 1 - • Loricaria sp. T nrira? LSDE 4 - - - - 3 2 Loricaria cataphracta * L on cat 4 - - 2 2 13 5 Peckoltia vittata x CCK.OH 4 10 2 4 3 1 1 Pspudonrwlpniv apnihnrhiv * i/ic(cl/i.i rtrf(l/Uf (y* -) Pseudge t enc 3 5 3 - - - ■ Ptevygoplichthys gibbiceps Pterygi 3 5 3 - - 4 1 Rine loricaria cacerencis ivinc-cac 4 - - 1 1 - ■ Rineloncaria phoxocephala I? inpnKri IUIUI 1U ucne IvldLJE, 4 - - - - 8 6 Caiophysus macropterus Cfllrmhv v.- <\J yr^fliy LSPI 1 30 7 10 7 13 4 Hemisorubim platyrhynchos T ^PT 1 12 7 6 4 49 9 Paulicea lutkem r dunce T 9PT 1 - - - - 1 1 Ph ractocephalus hemiolioptexus * I UNCHj T QPT 1 - - 1 1 . ■ Pinirampus pitinampu l III 11 dill 1 31 11 12 9 - ■ Platvnetn/itirhthw nntsitnv Platyno T CDT 1 4 4 14 5 6 4 PsPLldnnlfllXKtnmn fnvrintum * ■ c *****sfsuMj'jt huh jlULltilUrfl rseUupt T CDT 1 1 1 3 2 5 4 Pseud onlntvstnmn tiorimim * i**+v[ft**tjr<3 tisrf nt tile' iiitif/l Pseudpt T CDT 1 7 4 2 2 1 1 Sorubimichthys planicep s OUI Lipid LjI 1 1 1 1 - - 3 2 Pitnelodina flavipinnis r l mci Id I COW 4 - - 1 1 ■ Pimelodella sp. 1 * r imeia i I CPT Lor 1 4 i 8 Pimelodus albofasciatus PlTTirf* ln;i 1 Jlllk.lv.fU MS ON 4 in 8 2 2 Pimelodus blochii Pimelob LSON 4 L £ - Pimelodus ornatus Pimelor LSON 1 1 1 4 2 Pimelodus sp. 1" Pimespl MSON 4 128 14 219 14 . Pimelodus sp. 4 Pimesp4 SSON 4 • - 1 1 12 7 Platxstntnnlirhlhw vturin Platyst 4 - - 1 1 - - Sorubim lima* Sorulim 4 83 13 110 13 2 2 7 rirhrtmvrtpru v cr» 1 Trichom SSPI 4 - - . - 1 1 Pvpiifi/it\'I/ifijnic i»i ■ ■/• »-j-«m »■ Pseudmi LBEO 4 - 1 1 - Aequidens viridis * Aequivi MCIO 3 2 Biotodoma cupido Biotodo SCIO 4 9 3 28 10 Chaetobranchus flavescens Chaetob LCK 4 4 1 1 1 Cichla mono cuius Cichlam LOP 1 8 4 8 6 17 10 Cichla temensis Cichlat LCIP 1 23 8 Crenicichla johanna Crenijo LCIP 3 4 2 2 2 Crenicichla lenticulata Crenile LCIP 3 27 10 5 4 8 2 Classification Hypophthalmidae Loricariidae Pimelodidae Trichomycteridae Beloniformes Belonidae Perciformes Cichlidae 59 Table 3-3 — continued. Classification Species Species Guild Quality Jamari Candeias J. Parana code rank n Samples n Samples n Samples Crenicichla proteus Crenipr LCD" 3 - - 1 1 Geophagus megasema Geophme LCIO 2 ■ - 33 10 Geophagus cf. proximus' Geophsu LCIO 2 71 12 115 12 Heros spurius Herossp MCIO 3 4 4 3 2 Hypselecara temporalis Hypsele MCIO 4 1 1 Mesonaula festivus Mesonau SCIO 4 1 J Salanoperca jurupari Satanoj MCIO 2 4 3 12 6 17 6 Sciaenidae Plagiosaon squamosissimus Plagios LSCP 1 7 5 21 11 5 5 Pleuronectiformes Pachypops sp. 1 * Pachypl LSCO 4 1 1 Achiridae Achirus sp. Pleuron LPLP 4 2 2 1 1 Total number of fish excluding / including samples of May 1993 3828 / 6772 2779 / 2779 3616/4506 Total number of fish species excluding / including* samples of May 1993 106/H9* 122/122 121 / 122** Total number of samples excluding / including May 1993 (14 gill nets / day) 18/24 11 S/18 18/20 Note: An wa" indicates species-groups (see text for explanation) Opportunistic predation on gill-netted fish accounted for an estimated loss of 20.9 kg of fish between November 1993 and November 1994, or 1.7% of the corresponding yield. About 17.3% or 1399 of the fish captured during this period were mutilated by opportunistic predators, 53% of these mutilations were restricted to the membranous portion of the caudal fin, 27% were represented by major mutilations in the caudal peduncle and body, and 9% consisted of major mutilations restricted to the caudal peduncle. Between August 1993 and November 1994, the Jamari, the Candeias, and the Jaci-Parana River yielded 3828 fish (711.2 kg), 2779 fish (410.0 kg), and 3616 fish (366.3 kg), respectively (Table 3-3). Most of the following results will be based on samples from August 1993 through November 1994 (six field surveys), when a definitive sampling procedure started to be used. 60 General Characteristics of the Gill Net Surveys Figures 3-3 and 3-4 present the average number of fish per class of standard length and weight for the three studied rivers, respectively. The Jamari River usually yielded a greater number of larger fish (SL > 20 cm, weight > 0.2 kg). The total number of fish captured throughout the duration of the study varied temporally and spatially (e.g. November 1994 in the Jamari and Candeias River, and August 1993 in the Jaci-Parana) . Extreme variations were associated with fluctuations in the abundance of small-sized fish. A greater abundance of large fish in the Jamari River is also indicated by a greater mean yield (as weight) per day of larger mesh sizes (35-55 mm) , particularly for 35 mm gill nets (Figure 3-5) . In the Candeias and in the Jaci-Parana River the 25 and the 3 5 mm mesh sizes had lower and similar mean yield. In terms of average number of fish captured per day per mesh size, the Jamari and Candeias tended to have greater and similar yields for the 15 and 25 mm mesh sizes, whereas in the Jaci-Parana the 15 mm gill nets yielded an average of 3 times more fish than the 25 mm mesh size. Diel variation in yield among the three rivers is shown in Figure 3-6. On average, greater yield (in number and in weight) occurred at 1800 hours (for the three rivers) and lowest at 1200 hours (except for the Jaci-Parana River, which tended to have lowest yield at 000 hour) . Even though greater captures at 1800 can be related to the fact that it corresponded to the first time gill nets were inspected for fish, records from three days of continuous sampling at site J2 of the Jamari River carried out on May 1993 indicate that the time of the day between 1200 and 1800 hours normally produces greater yield (Figure 3-7) . 61 300 280 260 240 220 200 180 160 140 120 100 80 60 40 20 August 1993 November 1993 February Jamari River 1 19941 May 19 1994 II August 1994 S Nov. 1994 300 n 280 ■ 260 - sh 220 ■ 200 ■ o 180 - a> leo • 140 - E 120 ■ 100 ■ c 80 - c CO 60 - CD 40 ■ 20 - 0 - 300 ■ 2S0 ■ 260 • 240 ■ 220 ■ 200 ■ 160 ■ 160 ■ 140 ■ 120 ■ 100 - 80 - 60 - 40 - 20 - 0 - Si Candeias River Sl (261 I 359) n ^■7 i Jaci i.p arana River 1 Ik,, o o o o o o £23221 O O O O O O *~ 9 ■? T V 66000 V 000000 •j1 « n f » * 66606 u r- «\i « A 00000 00000 tN| « ^ ■ tO 6606 J! 000000 r N ri ^ 1(1 1(1 66606 U ^ N rt ^ Classes of standard length (cm) Figure 3-3: Mean number of fish (± SD) per classes of standard length from August 1993 to November 1994 in the Jamari, Candeias, and Jaci- Parana rivers (n=3 sites per river per field campaign) . 62 220 200 1(0 160 140 120 100 80 60 40 - 20 0 August 1993 . November 19931 . (344 ±384) O O O O O Q ^- N « V lO « i 6 o « 28! Jamar Feb. 1994 (132 ±172) River May 1994 Q0i$B . August 1994 I Nov. 1994 (153 ±168) Candeias River Jaci-Parana Rive O Q O O O Q »- w n ■» « « O O O O O Q w (0 t ifl JS O O O O O Q N n ^ in in Classes of weight (kg) Figure 3-4: Mean number of fish (± SD) per classes of weight from August 1993 to November 1994 in the Jamari, Candeias, and Jaci-Parana rivers (n=3 sites per river per field campaign) . 63 6 - „ 10 O) S — 8 - > s <» 0 ^ 80 - a i= 70 - O so- g 50- s *°- t 30- C 20- 1 O 10 - 2 oi Jamari River II [1 15 25 35 45 55 Candeias River Jaci-Parana River ii i 15 25 35 45 55 Mesh size (mm) [HI [in (66 ±117) m 15 25 35 45 55 Figure 3-5: Mean yield (± SD) per gill net mesh size in the Jamari, Candeias, and Jaci-Parana rivers (n=3 6 gill net days for the 15, 25, and 35 mm mesh sizes; and n=72 gill net days for the 45 and 55 mm mesh sizes) . Jamari River 24 22 1 20 16 s 16 ] 14 >- 12 B 10 to 6 2 6 4 2 0 01 Candeias River Jaci-Parana River rL £1 fish) 180 - 180 - o 140 - (no. 120 - 100 - ] 80 - 60 - Mean 40 - 20 - 0 - Ma — i i n 18 0 6 12 Time of the day (98 ±139) Mil 16 0 6 12 Figure 3-6: Diel variation in yield (mean ± SD, n=18 days) in the Jamari, Candeias, and Jaci-Parana rivers. 64 140 12 18 0 6 12 18 0 6 12 18 0 6 12 Time of the day Figure 3-7: Cumulative yield (as weight and number/gill net set) of fish during a three-day long survey in the Jamari River (site J2) , and during a two-day long survey in the Jaci-Parana River (a location near site P3) . This trend, however, may not be as evident in some circumstances, as when only one very abundant crepuscular species (Auchenipterichthys thoracatus) dominates the catches (89% in number - 790 individuals; and 37% in weight - 10.0 kg), as seen in the same figure for a two-day long survey in the Jaci-Parana River in May 1993 (Figure 3-7) . The Jamari and Candeias rivers were also similar with respect to diel variation in the mean relative number of captures of the most abundant fish groups (clupeids, characoids, siluroids, and cichlids) (Figure 3-8), but quite distinct from the Jaci-Parana River, specially regarding clupeids and characoids. The relative number of clupeids and characoids in these three rivers seem to correlated, and it is evident that large clupeids in the Jaci-Parana River, as opposed to the other 65 Time of the day 18 VZZA 0 6 E25S 12 Jamari River - Can dei as R Jaci-Parana R. - Clupeidae 20 - 1 V 40 60 80 100 Characoidei 20 I 40 I 1 — 60 80 100 Siluroidei Cichlidae Jamari River Candeias R. - Jaci-Parana R. - i i i i 20 40 60 80 100 i 1 1 i — 20 40 60 80 100 Mean relative number (%) Figure 3-8: Diel variation in the mean relative number of clupeids, characoids, siluroids, and cichlids captured in the Jamari, Candeias, and Jaci-Parana rivers (n=18 days) . two rivers, are much more active during daytime hours. This difference appears to be related to the fact that Pellona flavipinnis , which is very abundant and seems to be more active during night time in the Jamari and Candeias rivers (pers . observation) was very rare in the Jaci-Parana River (only one individual was captured in this river during this study, Table 3-2) . The other clupeid species, P. castelnaeana, was quite abundant in the Jaci-Parana River, and its capture pattern tracked that of characoids. Gill Net Yield of the Regulated Jamari River in Relation to Two Free- flowing Rivers Seasonal variation in yield as total weight, number of fish, and number of fish species per day of sampling in the study rivers is shown 66 in Figures 3-9, 3-10 and 3-11, respectively. A general trend towards a reduction in yield parameters (weight, number of fish, and number of fish species) during the flood season (February) is quite evident in the Jaci-Parana River. A drop in yield during the flood season is not as conspicuous in the Candeias River, where the seasonal variation of yield parameters was very attenuated when compared with the other two rivers . Still, total weight, number of fish, and fish species were lower in February and May (receding waters) . Sampling sites of the Jamari River yielded the lowest number of species in February, but August tended to produce less fish in weight and in numbers, particularly August 19 94, and specially for the two sites closest to the dam (Jl and J2) . Jamari River t 1 1 1 1 r Aug 93 Nov. F* M May Aug Nov Figure 3-9: Seasonal variation in yield (total weight/gill net set/day) in the Jamari, Candeias, and Jaci-Parana rivers. 67 Jamari River ^ Candeias River Figure 3-10: Seasonal variation in yield (total number of fish/gill net set/day) in the Jamari, Candeias, and Jaci-Parana rivers. Figure 3-11: Seasonal variation in yield (total number of fish species/gill net set/day) in the Jamari, Candeias, and Jaci-Parana rivers . 68 Yield (as weight) of the Jamari River site J3 between August 1993 and August 1994 showed opposing trends in relation to the other two sites, the ones closest to the dam. Even though not distinguishable when analyzing seasonal variation in the number of fish and number of fish species captured, this pattern might be an indication that the reduction in water quality during the dry season caused by the operation of the dam is forcing the fish to move downriver in search of better quality waters . Despite the known alterations in water quality and in the hydrological regime of the Jamari River, this river normally produced more fish. The yield of the Jamari (as weight) was nearly twice as great (39.5 kg/gill net set/day) and significantly different (nested ANOVA, P=0.0002; Tukey P=0.05) than that of the Candeias (22.8 kg/gill net set/day) and Jaci-Parana rivers (20.3 kg/gill net set/day) (Table 3-4). Table 3-4: Results of the nested ANOVA for testing for differences in yield (as weight, number of fish, and number of fish species/gill net set/day) among the studied rivers. Yield (as kg / gill net set / day) Mean Effect DF F River 2 10.56 Site (river) 6 0.95 P 0.0002 0.4725 Jamari River 39.5 Candeias River 22.8 J. Parana R. 20.3 Yield (as number of fish / gill net set / day) Mean Effect DF F River 2 0.95 Site (river) 6 1.77 P 0.3953 0.1276 Jamari River 196.5 Candeias River 145.1 J. Parana R. 139.3 Yield (as number of fish species / gill net set / day) Mean Effect DF F River 2 0.75 Site (river) 6 1.06 P 0.4773 0.4006 Jamari River 32.6 Candeias River 36.3 J. Parana R. 32.9 69 The Jamari River also tended to yield a greater number of fish, and a lower number of species when compared with the other two rivers, but these differences were not significant (Table 3-4) . Comparison of Gill Net Samples from the Jamari River Before and After Dam Construction Figure 3-12 presents the results of the comparison between yield before and after regulation of the Jamari River carried out by two procedures (gill net sets composed of 4 shared mesh sizes, and gill net sets of approximately the same mesh size composition and composed of 10 nets) . Comparatively, both procedures produced quite similar results, and only the one that includes catches of 10 gill net sets will be considered further here. In general terms, the mean number of fish per sample increased significantly, and nearly 4-fold after regulation, when considering the site located closest to the dam (Jl) . This site is also the one that more approximates the location of the sites sampled before the regulation of the Jamari River. Mean yield (as weight) per sample also increased significantly, but only about 30%, when comparing pre-dam (JB) and post-dam (Jl) mean. The mean number of species per sample went from 22 before regulation to 28-31 species after regulation, but this difference was not significant (largely due to the wide variation in the mean number of species captured on pre-dam surveys, range 8-42 species/gill net set/day) . It is also evident from Figure 3-12 that the dam produced a concentration of fish in river reaches immediately downstream (Site Jl) , and their concentration fell significantly progressing down the river (sites J2 and J3) . Furthermore, yield (as weight) of these two sites 70 Figure 3-12: Mean yield (as total number of fish, total weight, and total number of species/gill net set/day) before (JB, hatched bars) and after (open bars) regulation of the Jamari River (error bar = SD) . The three sampling sites in the Jamari River sampled after regulation were located 2 (Jl) , 21 (J2) , and 33 (J3) river kilometers downstream from the hydroelectric dam. approximated quite closely that recorded during pre-dam surveys . On the other hand, and considering the mean number and the mean weight of fish for the 10 gill nets comparison, the mean weight of an individual fish at the general location that corresponds to the Samuel Dam (JB and Jl) dropped from 351g pre-dam to 138g post-dam (or 60%) . Results from J2 and J3 when compared with JB indicate a drop of about 50% in mean weight of fish. The hypothesis of a general reduction of the mean weight of fish species captured at the river location that corresponds today to the 71 Samuel Dam was tested by matching before and after data sets for fish species captured with the same mesh size. Testing was based on the assumption that the known selectivity of gill nets for fish of certain sizes would randomly draw a representative sample of the size structure of fish populations before and after regulation. There were 38 matches between pre- and post-dam data sets, 27 of these corresponding to a greater weight (or mean weight) of fish species caught before river regulation (Figure 3-13) . A Sign Test applied to these 38 matches rejected the null hypothesis that there was no difference in weight (or mean weight) of fish species captured with the same mesh size before and after the regulation of the Jamari River (Co.osm ,38=12 , P=0.05). A comparison of the 20 most important species (in yield rank by weight and numbers) is shown in Table 3-5. About a third of the 20 most important species in yield as weight caught during gill net surveys before impoundment were among the 20 most important species after impoundment. Considering yield by number, the 22 species that ranked among the most important after regulation included 11 of the 30 fish species ranked as most important before regulation. Of the 33 species ranked among the 20 most important species in weight and number during pre-dam surveys, only two (Myleus sp. 1 and Lycengraulis batesii) were not recorded in the Jamari River in post-dam surveys (Osteoglossum bicirrhosum was not collected during post-dam surveys, but it was observed swimming near the water surface in several occasions, pers . observation) . 72 Before regulation After regulation Species (mesh size) 2C 1C J3 C 1C 1: 8051 ir 11 2C (ZD3 1L 1C 6(115 mz)9 1C 1C 1C]28 2C 1C ir 3L 5C 14C 3C 1L 1C 2C 49TJ1 n r 2C 35 32 D4 □6 34 36 □13 32 D9 D4 1CD1 34 □24 367 1CD4 34 □111 □31 32 □2 32 8 15 J6 3C^1 1(=^7 J1 Bouleoc Bouleoc Brymela Brymela Chalceu Cichlam Geophsu 15)- '25 35) '45 15) '45) '2i Geophsu (35) Geophsu (45) Hemisop (25) Hemiuni (15) Hemiuni (25) Hemiuni (35) Hydrope (35) Hydrosc (45) Laetaen (1 5) Lepofas (25) Lepofas (35) Lepofri (25) Lepofri (45) Lepokla (15) Paragal (35) h Pellonc (55) • Potamal (35 Potamla (35 Psectrc (35) Pseudge (45) Rhaphiv (35) Rhaphiv (45J Semathe (35) Serrasr (35) Serrasr (55) Sorulim (25 Tripoag (25 Tripoag (35 Tripocu (25 - Tripoel (25) - Tripoel (35) 1.2 0.9 0.6 0.3 0.0 0.3 0.6 0.9 1.2 Weight or mean weight (kg) Figure 3-13: Weight or mean weight of fish species captured with the same mesh size during gill net surveys carried out in the Jamari River before and after regulation (species/mesh size combinations with a lower weight on pre-dam surveys indicated by a sign) . Numbers next to bar indicate number of fish, species codes as in Table 3-3. 73 Table 3-5: The most important fish species (in yield by weight and by number) of the Jamari River recorded during pre- and post-dam gill net surveys. Number between parenthesis indicates the species rank before regulation of the Jamari River. Species codes as in Table 3-3. KanK Yield by weight Yield by number Before After d eiore 1 Bouleoc Knapniv (/) \ ft 1 ?1 ill 1 1 Of Myieusz fVntrnm (1K\ 2 Serrasr rellonc (zl) i npoag Rhanhiv Hit 3 Hydrosc rotamla (31; DOUlcOC Pntamla OCto rUulillia \tAj) 4 Brymela Mylodur Q prrocr nA vlnHur c J riyuroi Piniram DiyillCla Chalwn Clfll 6 Myieusz rtyarosc (j) T)f"t7TV>Gll DI V JX-MJ 7 Rhaphiv AgeneiD (zi) iwyicusi l^aCIilUVa \jy J 0 8 Myleusl reiioni tz**; OGIildUlC Pi mpcnl 1 1111L ^J. ' 1 9 S em a the Comer /O \ oerrasr tz; r SCWJXC / /\uL>IiLilU V_- Ul 111 1 tXTv 10 Prochin ^ematne (V; cnaiceu I4pimiini f l /I ^ nciiiiuiii v*"/ 11 Pseudge Lepofas (15) Rhaphiv / Prochin Sorulim (12) 12 Osteogl Laemova (44) Hydrosc / Sorulim Pellonf(21) 13 Serrsp2 Pseudni (35) Brybrev / Boulema Geophsu (15) 14 Brybrev Prochib Lepofri / Hemiuni Psectrc (28) 15 Lepofas Lepofri (16) Geophsu Lepofas (18) 16 Lepofri Geophsu (29) Serrsp2 Semathe (8) 17 Cichlam Curimak Hydrol Eigenma 18 Hopliam Tripoel (47) Lepofas / Laetaen / Lycengr Serrasr (4)/Potamal(20) 19 Crenijo Calophy (34) Cichlam / Crenijo Tripoel (25) / Hemiima 20 Platyno Potamal (32) Potamla / Potamal / Acesmic Prochib The rearrangement in the importance of species caught in gill net surveys resulted in a reduction on the mean yield (as weight) of high quality species after regulation of the Jamari River (Figure 3-14) . Species with high market value, notably Brycon spp. and Cichla monoculus, dropped in importance after regulation (they ranked 27th and 38th in yield as weight, 7 . 0 kg and 4 . 5 kg respectively) . Only in November of 1993 was the mean yield of high quality fish in the Jamari River higher than that of pre-dam surveys, and not that much (4.6 kg/gill net set/day vs. 4.0 kg/gill net set/day). Therefore, the maintenance of yield in the Jamari River was largely a consequence of an increase in the presence of fish species of low market value in the catches (e.g. the carnivore Rhaphiodon vulpinus and the detritivore 74 Jamari River Before dam Aug. 1993 Nov. 1993 Feb. 1994 May 1994 Aug. 1994 Nov. 1994 c o 2 Aug. 1993 Nov. 1993 Feb. 1994 May 1994 Aug. 1994 Nov. 1994 -i r Candeias River Aug. 1993 - Nov. 1993 Jaci-Parana River Feb. 1994 -Q3 May 1994 - Aug. 1994 - Nov. 1994 - Quality rank 1 2 3 * 20 I 30 I 40 0 10 Mean yield (kg/1 0 gill nets/day) Figure 3-14: Seasonal variation in mean yield (kg/10 gill nets/day) of fish ranked according to market value (1 = high, 2 = medium, 3 = low, and 4 = no market value) for the Jamari, Candeias, and Jaci-Parana rivers. See Table 3-2 for assignment of fish species to quality rank. Potamorhina latior, Table 3-5) . These two species accounted for 27% of the 711 kg of fish captured in the Jamari River between August 1993 and November 1994. During August and November the other two rivers, whose overall yield (as weight) was significantly lower than the yield of the Jamari, produced an amount of high quality fish comparable to that produced by the Jamari. August, a month that was normally associated with high catches in the Candeias and in the Jaci-Parana River, was the month that 75 produced, on average, less fish in the Jamari River. This is also the time of the year when water quality of the Jamari River is the lowest. The Fish Fauna of the Jamari River Before and After Regulation Additional records from gill net surveys carried out between September 1986 and December 1987 reinforces the fact that fewer species were present at a given time in the Jamari River before regulation (Table 3-6) . Records for the Candeias River taken during the same surveys were included in this table for comparison purposes because the number of gill nets and the mesh size composition of gill net sets were different from those used in the present study and also from those used by Santos (1991) (see note in Table 3-6) . Table 3-6: Total number of fish species captured during gill net surveys carried out between September 1986 and December 1987 by SONDOTECNICA in the Jamari River (site MJ1, upstream the Samuel Waterfalls; site JJ, downstream the Samuel Waterfalls) and in the Candeias River (site RC, lower Candeias River) . Date \ Site MJ1 JJ RC September 1986 28 14 2S November 1986 18 26 49 June 1987 19 23 41 October 1987 14 24 41 December 1987 16 37 39 Mean±SD 19.0 ±5.4 24.8 ± 8.2 39.6 ±7.5 Source: ELETRONORTE/ SONDOTECNICA (1987) . Note: Gill net sets composed of 13 nets with mesh sizes ranging from 15 to 90 mm were used in these surveys. The mean number of fish species per sample in the Candeias River in these pre-dam surveys (39.6 ±7.5) is quite similar to the mean recorded during this study (41.9 ±7.1 considering only the samples 76 taken during the dry season, which corresponds to the dates of these pre-dam surveys; or 36.3 ± 10.2 considering all samples). The close approximation between the mean number of species per sample in the Candeias River before and after the regulation of the Jamari River indicates that records for the Jamari River obtained with a different arrangement of gill nets are not biased. Finally, it appears that the pre-dam, river channel species pool was quite reduced when compared with the post-dam species pool since new species tended to accumulate at lower rates (Figure 3-15) . Conversely, species accumulation rates for 0 1 2 3 4 5 6 7 8 9 10 1 1 12 13 14 15 16 17 18 Number of samples Figure 3-15: Species accumulation curves for the Jamari River (before and after impoundment) , the Candeias River (before and after the regulation of the Jamari River), and the Jaci-Parana River. Santos' records for cumulative number of species from the Jamari River before impoundment based on gill net sets composed of 10 gill nets (Santos 1991), SONDOTFXNICA' S records for cumulative number of species based on gill net sets composed of 13 gill nets ( ELETRONORTE/ SONDOTI2CNICA 1987) . All other cases based on sampling with gill net sets composed of 14 gill nets . 77 the Candeias River before and after regulation of the Jamari River are indistinguishable from each other. Even today, the Jamari River appears to have fewer fish species than the Candeias and the Jaci-Parana rivers (Figure 3-15) . Except for the records from the Jamari River before impoundment, cluster analysis indicated that each studied river had a distinct fish fauna (Figure 3-16) . The clustering of the sampling sites studied in this investigation follows a pattern that resembles the degree of isolation among river drainages, with the fish fauna of the Jamari and P3 P2 P1 JB J3 J2 J1 C3 C2 C1 10 40 70 Similarity Figure 3-16: Faunistic similarity among the fish fauna occurring at the sampling sites of the Jamari River (JB, Jl, J2 , J3 ) , Candeias (CI, C2, C3), the Jaci-Parana River (PI, P2, P3). Site JB corresponds to the fish species composition of the Jamari River before impoundment (Santos 1991) . Clustering based on Jaccard's similarity index, using the weighted mean average method. 78 its tributary being more similar to each other than to the fish fauna of the Jaci-Parana River. The Jamari River "site* that corresponds to the fish fauna present before regulation (JB) showed, however, a greater resemblance with the Jamari /Candei as system fish fauna as a whole rather than with the fish fauna present now in the Jamari River. This pattern indicates a great change in fish species composition of river channel assemblages after regulation. The clustering of all records of species occurrence throughout the Jamari River basin before (BF) and after regulation (AF) is shown in Figure 3-17. Pre-dam surveys included two types of natural habitats (river channel, backwater lakes), tributaries located upstream (UP) and downstream (DO) from the Samuel Waterfalls, and records from an artificial channel that was built to divert the course of the Jamari River during the construction of the Samuel Dam (Santos 1991, Appendix A) . This cluster analysis indicates that the fish fauna recorded in the Jamari River after regulation has greater similarity with the fish fauna that occurred in side lakes located downstream from the Samuel Waterfalls before regulation, followed by the fish fauna that occurred in the river channel downstream from the Samuel Waterfalls. A second cluster analysis (not shown) performed using only samples from site Jl, which corresponds approximately to the locations sampled during pre-dam surveys, showed a greater similarity between river channel fish fauna before and after impoundment, and these in their turn clustered with backwater lakes before impoundment. Jaccard's Similarity Coefficient between river channel fish fauna before and after regulation, and between river channel fish fauna after regulation and backwater lakes before regulation were nearly identical (0.396 and 0.380, respectively). 79 Artificial channel (BF) ■ Tributaries (DO/BF) I Lakes (UP/BF) I Tributaries (UP/BF) I Channel (UP/BF) I Channel (DO/BF) I Lakes (DO/BF) Channel (DO/AF) I 1 1 1 6 40 70 100 Similarity Figure 3-17: Faunistic similarity among the fish fauna of several biotopes of the Jamari River downstream (DO) and upstream (UP) from the Samuel Waterfalls (that corresponds today to the location of the Samuel Dam) before (BF) and after (AF) impoundment. Clustering based on Jaccard's similarity index, using the weighted mean average method. Pre- dam occurrence records after Santos (1991) , see also Appendix A. Therefore, the fish fauna found in this location after impoundment includes faunistic elements that were recorded only in lacustrine habitats downstream from the dam (Psectrogaster curviventris , P. rutiloides, Curimatella meyeri, Eigenmannina melanopogon, Hemiodopsis microlepis , Prochilodus cf. beni, Pterygoplichthys gibbiceps, Pinirampus pirinampu, Pseudoplatystoma tigrinum, Pimelodus sp. 1, and Chaetobranchus flavescens) . Other species are added to the list if we consider all post-dam records for the Jamari River (Appendix A) . 80 River Fish Assemblages: Their Responses to Natural and Artificial Environmental Gradients The species-based and STF guild-based DCA ordination of samples from August 1993 to November 1994 (54 samples) showed very little variation and displayed largely the same information (DCA Axis I of the species-based DCA was significantly correlated with DCA Axis I of the STF guild-based DCA - r=0.90, P<0.0001, n=54; and DCA Axis II of the species-based DCA was significantly correlated with DCA Axis II of the STF guild-based DCA - r=0.58, P<0.0001, n=54) . Figures 3-18 and 3-19 show the ordination of sites using the species based DCA (species with less than five occurrences were not included in this analysis) and the correspondent species plot, respectively. DCA Axis I of this first ordination emphasized the faunistic difference between the Jaci-Parana River and the Jamari-Candeias River system (15 of the 110 species included in this ordination occurred only in the Jaci-Parana River) , whereas sample scoring on DCA Axis II largely described a seasonal pattern where samples from the dry season within the same river system (samples **2, **3, **6, and **7, or August 1993, November 1993, August 1994, and November 1994, respectively) tended to score high on the axis, and samples from the flood season (**4 and **5, or February and May 1994, respectively) tended to score low. The faunistic difference between the Jaci-Parana and the Jamari-Candeias system also corresponded to differences in occurrence of functional, structural groups as defined by STF guilds. Whereas the Jaci-Parana River fish assemblage included many small to medium-size fish of a variety of taxa and food habits, the Jamari-Candeias River assemblages were characterized by large fish (Figure 3-20) . 81 4 -i 117 3 - J27 J13 J37 J16 X < < O Q 2 - 1 - C37 C27J22 J36 C32C C33 C35 C16 jS54 J24 C14 C24 J25 P14 P27 P34 P2f, P13 P37 P25 P33 P32 P35 P24 C15 C25 DCA Axis I Figure 3-18: DCA ordination of 54 samples taken in the studied rivers. DCA based on raw abundance data of 110 species. Species with less than five occurrences were not included in this ordination (73 species corresponding to 240 fish, 1.5% of the total number of fish captured between August 1993 and November 1994) . Letter in site codes identify the river (J = Jamari River, C = Candeias River, P = Jaci-Parana River) . The first digit in the site code corresponds to the position of the site within the river (1 = upstream-most site, 2 = middle site, 3 = downstream-most site) . The second digit in the site code corresponds to the sample date (2 = August 1993, 3 = November 1993, 4 = February 1994, 5 = May 1994, 6 = August 1994 and 7 = November 1994) . Site codes followed by an underscore were moved to facilitate reading. 82 Mylodur Cunmajk 4.0 - Psactrc Ps»ctrr Potamal 4»miima Myloa | 2.5 < < O Q 1.0 - Potamla TrpocuP* onf Hypophe Hpopth ■0.5*ntrom -0.5 — ' udpt_ Pfmeloa_ Ps»udni_ Laetaen Cunmai Trpoel Piniram Calophy Piniram Sttispl P'ochb_ Mytousl Hydrops _ HemidoHerossp Pim«sp1_ Plagios Packolt CrenilG Rhytisp Cichlam Ssmathe HyposC lepokja Laemova Serrase Ca«notrsert^2,n~ lepofas Myleus3_ H.misop P,m,ta1 Dorasl Rosbthu _ Geophsu_ Opsotn Platyno Rhaphig Biotodtu R°*'?nu Hydros,?™"'- S>",n°l PW$$gP™ °psostu JLL. Cunmar .J TBUm r-.orm.lh Acestar Argos'ca rosp Opsohum Brymala Bout«ma loruii 7 ™.i Agenaiu Auchnuc. Ag»nmb Mytoupa Mylsus2 P»Nonc Ae«h«L Curmalb. Pseudtr "o9^^"'*- Hypost! Hemiuni Hopliam. "TO™™, Auchtho Hamioac A»smicMyP0P9u Hemiarg Agensp3 Agensia Mo top id Bryabu Brybr.v Brypasu Paragal_ Agoniat Rhytio. Astyant Eigenma 1.0 2.5 DCA Axis I 4.0 Figure 3-19: Species plot correspondent to the ordination shown in Figure 3-18. Species code as in Table 3-3. Species codes followed by an underscore were moved to facilitate reading. Furthermore, the distinction between low water and high water season assemblages corresponded to an increase in the occurrence of large characoid (LCPK) and siluroid planktivores (LSPK) (notably Hypophthalmus spp. and Eigenmannina melanopogon) in river channel assemblages of all studied rivers (Figure 3-19 and Figure 3-20) . 83 Figure 3-20: STF guild plot correspondent to the ordination of 54 samples by DCA using raw abundance data of fish collected between August 1993 and November 1994. Guilds with less than 10 occurrences excluded from the analysis (eight guilds corresponding to 34 fish, 0.33% of total number of collected fish). STF guild codes as in Table 3-3. Guild codes followed by an underscore were moved to facilitate reading. A second set of ordinations (only sampling site ordination based on raw species abundance data is reported here) excluding samples from the Jaci-Parana River revealed, again, the distinction between high water (scored lower on DCA Axis I) and low water (scored higher on DCA Axis I) river fish assemblages (Figure 3-21) . Correlations between site scores and environmental variables corroborates this interpretation. The first DCA axis was strongly correlated with mean river depth (r=-0.75, P<0.0001, n=36) and with the standard deviation of water temperature (r=0.60, P<0.0001, n=36), and these two environmental variables in turn, were the ones best correlated with season (mean river depth, r=0.68, P< 0.0001, n=36; standard deviation of water temperature, r=0.62, P < 84 3 "I 2 - JB < O □ J 4 1 - J24 J34 C14 C1S 025 J13 J37 J33 C37 J23 J27 J15 J36 J17 C24 J25 J35 C33 J1§32 J22" J26 C22 016 C1^7 DCA Axis I Figure 3-21: DCA ordination of samples from the Jamari and Candeias River. Site codes as in Figure 3-18. 0.0001, n=36) . The second DCA axis tended, however, to split samples from the Jamari River from those of the Candeias River, specially those samples from the dry season (samples **2, **3, **6, and **7) . Accordingly, this axis showed strong correlations with those physical variables that best characterized differences between the Jamari and the Candeias River (absolute daily water level variation, r=0.55, P=0.0006, n=36; and mean dissolved oxygen concentration, r=-0.51, P=0.0016, n=36) . Even though these two variables reflect important alterations brought about by the regulation of the Jamari River, the scoring of the samples along the second DCA axis does not make evident the presence of a gradient in fish assemblage response to regulation. 85 The strong interference of natural seasonal shifts in river fish assemblages, which was evident in the first and second ordinations, was eliminated in a third set of ordinations by excluding samples from the flood season (February and May) in the Jamari and in the Candeias River. The species-based ordination of dry season samples is shown in Figure 3- 22, and the corresponding species plot in Figure 3-23. The site scores of the first DCA axis of the guild-based ordination were significantly correlated with the site scores of the species-based ordination (r=0.62, P=0.0012, n=24) , whereas the site scores for the second DCA axes were poorly correlated (r=0.01, P=0.9775, n=24) . Only the first DCA axis scoring of the guild-based DCA will be used to interpret the ordination of sites. This third ordination presents the Jamari and Candeias River sites quite apart from each other, with sites from the Candeias River scoring lower on both axes and the ones from the Jamari scoring higher. This separation reflects differences in species composition, and also differences in the occurrence of functional groups (STF guilds) . In general terms, the Candeias River tended to aggregate certain species and functional groups that were either absent or not common in the Jamari River (e.g. Cichla spp., Satanoperca jurupari, Boulengerella maculata, Curimata roseni, Hemiodontichthys acipenserinus , Opsodoras humeralis, Acestrorhynchus heterolepis , Centromochlus heckelii, Lycengraulis batesii, Bryconops alburnoides , and Caenotropus labyrinthicus) . These species belong to a variety of taxa and feeding groups, but share the characteristic of being medium to small size fish (except for the predators Cichla spp., B . maculata and A. heterolepis) . Judging by their constant frequency of capture throughout the dry 86 3 -i 2 - CO < O Q 1 - C J12 J13 J 36 J16 J22 J32 J33 J37 J26 J23 6C22 C13 U3B" 012 C17 J27 C27 C33 G3j?- 1 2 DCA Axis I J17 Figure 3-22: DCA ordination of 24 dry season samples from the Jamari and Candeias rivers. DCA based on raw abundance data of 71 fish species. Species with less than five occurrences were not include in this ordination (64 species corresponding to 169 fish, 3.6% of the total number of fish captured between August and November of 1993 and 1994 in the Jamari and Candeias rivers). Site codes as in Figure 3-18. Site codes followed by an underscore were moved to facilitate reading. 87 "x O Q Schizof Pect Herossp Hemisop Serrsp2 Semathe Pseudpt Brymela Crenile Acesfar Hydrosc SerrasfLepofas Ch; Geophsu Hemioac Sorulim . Satanoi B^ohu^ tin/7 Tt/ c f P ) tnenacugcister yri. iiru.iius \ ir j - - 4 1 20 6 i nayerta ooiicjuu \tr) 1 1 1 1 8 4 Tetra sp. ( P ) - - 1 1 - - Ch aracidi id ae Lharaciaium sp. ( B } 5 1 - - 3? 3 30 8 Ctenoluciidae Boulengerella tnaculata ( P ) 1 1 - - - - C urim atid ae Cufvnatopsis fnacvolepis ( B ) - - • - 1 1 CyphochaTax cf. plumbeus ( B ) - - 35 1 3 2 rj vnii/i^ii/iMr Fni/UMnrrr [ R \ v, \y rlCK. rUi f CMJ. jyllUrUyifj \0} - - 11 3 109 8 Steindachnerina cf. dobula (B) - - - - 2 2 LiieiruMdL finer mu sp. hid; ? 1 - - - - - - Eryinnniudc fioplias tnalabaricus [ G ) d 1 • - 1 1 4 3 Gasteropeiecidae A A* A 1 ■ ■ ■ -raff. -■ » / F5 V Lxtmegieiia martnae \ r j • • 1 1 3 1 H emiodon tid ae Parodontinae Apareiodon sp. 1(B) M J - - • - - ■ Apareiodon sp. 2(B) - • - ■ 59 7 ricinioQonunac Argonectes scapularis ( P ) - - 2 1 - - Henuodopsis semitaeniatus ( P ) - - 1 1 - • Hetmodus unmxaculatus ( P } ■ ■ 3 2 3 3 Lebiasinidae Ncmnostomus beckf ordi ( P ) 2 1 41 6 - - Cprrg C aim 1 H ap KA\]l*ur nrtnt /PI /»7 V*c UJ yUL U \ tr 1 ■ • • - 3 3 Serrasalmus eigenmanni ( G ) - • ■ - 2 2 \j y nil 1 u m urn ica A nip T"/~\ /~\ f 1 1" 1 Low Figure 4-4: Ordination of the sandy beaches of the studied rivers according to the first two principal component axes. Ordination based on the correlation matrix, using the mean number of species per taxonomic group. The association of the taxonomic groups with PC I and PC II is also indicated (not in scale) . Sandy beach symbols are the same as in Figure 4-3 . interpretation. This axis was highly associated with the miscellaneous group, which was composed of a variety of fish families (Eugraulidae, Belonidae, Sciaenidae, Achiridae, and Tetraodontidae) that tended to be more common in the Candeias River. Spatial Responses of Habitat-use Groups to River Regulation The assignment of fish species to habitat-use groups used for the analysis of species richness and fish abundance patterns along impacted and unimpacted rivers is shown in Table 4-2. The number of species within habitat-use groups differed greatly among rivers. The total number of habitat-generalist, benthic and pelagic species found in each river was as follows: 3, 4 and 18 in the Jamari River downstream from 130 the dam; 6, 13, and 37 in the Candeias; and 9, 31, 46 in the Jaci-Parana River. In the case of the pristine Jaci-Parana River, simple linear regressions did not detect any significant evidence of longitudinal gradients in the richness or abundance of habitat generalist and benthic fish species (Figures 4-5 and 4-6) . There was, however, a trend towards increasing abundance of pelagic species along the study reach (R2=0.59, P=0.07, Figure 4-6). Responses observed in habitat-use groups in the regulated Jamari River indicate that there was a gradient of increasing species richness (R2=0.73, P=0.03) and fish abundance (R2=0.63, P=0.06) of habitat-generalist species (Figures 4-5 and 4-6) . This gradient was associated with the attenuation of the physical and chemical alterations from the upper to the lower portion of the study reach (i.e. with increasing distance of sandy beaches from the dam) . Another, but opposed gradient, was detected for pelagic fish species richness (R2=0.85, P=0.01) and abundance (R2=0.69, P=0.04) along the Candeias River (Figures 4-5 and 4-6) . This decreasing trend in richness and abundance along the study reach paralleled the known gradient of increasing interference of the Jamari River on water levels in the Candeias River immediately upstream of its confluence with the Jamari River. Regression analysis did not detect any statistically significant relationships for benthic species richness and abundance along the Jamari and Candeias rivers. However, benthic species richness and abundance were very depressed in sandy beaches along the Jamari River downstream from the dam and to a lesser extent, along the Candeias River (Figures 4-5 and 4- 6, note different scales for fish abundance in Figure 4-6). Of 11 131 Lower Jamari River Habitat generalist species Candeias River Jaci-Parani River 1 r— i r e 12 • 10- 8" 8 - 0 6 - % 4- 1 2- Benthic species 1 — i — 1 -H 1 1 r 20 15 - 10 - 5 - 0 Pelagic species 10 — r- 20 Fr«oe$ P=0.01 —r- 10 "1 — 20 30 Sandy beach location (rkm) Figure 4-5: Relationship between mean number of species and sandy beach location for habitat generalist (circle), benthic (square) and pelagic species (triangle) along the Jamari, Candeias, and Jaci -Parana rivers. Location = 0 corresponds to the position of the most upstream sandy- beach within each river. Lower Jamari River Habitat generalist species R'aO.63 P.0 06 8 - 6 - 1 - 2 - 0 -■ Candeias River Jaci-Parana River e 6 - 4 2 0 § 2 a Benthic species ■§ 1S . Pelagic species 218 '15 §12 £ 9 6 3 0 — I — 20 ■ ■ ■ ■ ■ 1 1 I I I A R2-0 69 P-O.M 1 1 1 0 5 10 I 1 15 20 20 18 - 16 14 12 - 10 — r 20 R:.059 P-0.07 Sandy beach location (rkm) Figure 4-6: Relationship between mean fish abundance and sandy beach location for habitat generalist (circle) , benthic (square) and pelagic species (triangle) along the Jamari, Candeias, and Jaci-Parana rivers. Location = 0 corresponds to the position of the most upstream sandy beach within each river. 132 families and subfamilies of benthic fish species found in sandy beach habitats during this study (Characidiidae, Curimatidae, Parodontinae , Rhamphichthyidae, Apteronotidae, Aspredinidae, Callichthyidae, Doradidae, Loricariidae, Pimelodidae, Trichomycteridae, and Achiridae) , only three (Aspredinidae, Pimelodidae, and Trichomycteridae) were recorded from sandy beaches of the Jamari River downstream from the dam. These families were represented by only 17 fish, of which 15 were medium size (10-15 cm standard length) Pimelodus spp. (Table 4-2). Even though reduced, the diversity and abundance of pelagic species in the Jamari River were not as depressed as in the case of benthic species, whereas the abundance of habitat generalist species was highest in the lower Jamari (Table 4-2) . Species richness and abundance patterns of habitat- use groups indicate that benthic fish species were highly affected by environmental modifications imposed by the operation of the dam. Discussion The sandy beach fish fauna of the lower Jamari was severely affected by the alterations in the riverine habitat brought about by the Samuel Dam. The total number of species found in sandy beaches of the lower Jamari River (25) was half of that recorded in the Candeias River (56) and a third of that registered in the Jaci-Parana River (86) . The two sandy beaches of the upper Jamari that were sampled only on a few occasions yielded more species (31) than the six sandy beaches located downstream from the dam that were intensively sampled. Reduced diversity of riverine biota is a common consequence of river regulation by hydroelectric dams (Vanicek et al . 197 0, Trotsky and Gregory 1974, Cadwallader 1978, Jalon et al . 1994). Yet, whereas the distribution of 133 small fish species in sandy beach habitats was severely disrupted by the dam, many of the large river channel dwelling species recorded during pre-dam surveys were still present (Chapter 3) . These distinct responses to river regulation are most likely a consequence of differences in life-history traits of components of sandy beach and river channel fish assemblages . Life-history Traits and the Susceptibility of Amazonian Fish to River Regulation Species composition in sandy beach habitats of the study rivers differed markedly from that of the river channel. River channel assemblages consisted of medium to large-size species (Chapter 3), many of them recognized as migratory (e.g. characoids such as Mylossoma, Triportheus, Leporinus, Schizodon, Rhytiodus , Prochilodus, Semaprochilodus , Curimata) (Goulding 1980) , whereas sandy beach assemblages included small fish taxa typical of Amazonian streams (e.g. Henderson and Walker 1990, Silva 1995) but also found in rivers (e.g. Ibarra and Stewart 1989, Lowe-McConnell 1991b) where they are considered resident fish (Lowe-McConnell 1987). Juveniles (fish less than 5 cm standard length) of most medium to large-size species were rarely taken in sandy beaches of the studied tributaries of the Madeira River, indicating that rearing of these species takes place elsewhere. Only cichlids, which are recognized as a sedentary group of fishes (Bayley and Petrere 1989) , some leporins (Anostomidae) , and Lycengraulis batesii (Engraulidae) had juveniles taken from sandy beaches of the study rivers (pers. observation). The near absence of juveniles of medium to large- 134 size species in tributaries of the Madeira River has been noted by Goulding (1980) and Santos (1991) . In fact, small fish taxa and juveniles of medium to large-size species (many of them migratory) appear to have complementary distributions in Amazonian waters: Small-fish species are dominant in nutrient-poor rivers, such as the ones in this study, or the Negro River in the central Amazon; and juveniles of medium to large-size species are dominant in floodplains of nutrient-rich, Whitewater rivers such as the Amazon or Madeira rivers (Goulding 1980, Goulding et al . 1988). The complementary distribution of these two groups appear to be a consequence of limited production and inadequate food supply in nutrient-poor rivers. The unusual downriver reproductive migration carried out by several medium to large-size characoid species in some nutrient-poor rivers in the Amazon has been interpreted as a mechanism to place their young in more productive habitats of nutrient rich, Whitewater rivers, reducing competition with the small-fish fauna resident in nutrient-poor rivers (Goulding 1980, Goulding et al . 1988). This mechanism seems to be fundamental for explaining the distinct responses of small and large fish species assemblages to the regulation of the Jamari River. Environmental Alterations in the Jamari and Candeias Rivers The regulation of the lower Jamari River modified its hydrological regime, and this effect propagated into the lower reaches of its tributary, the Candeias River. Furthermore, dissolved oxygen concentration in the water of the Jamari River was low during the second 135 half of the year due to the closure of spillway gates and the continuous release of hypolimnetic water used for electricity production. Minimum DO requirements for freshwater fish depend on the species, age, and life processes (e.g. reproduction, growth, etc.), but recommended annual 50-percentile and 5-percentile levels should be greater than 5 mg/1 and 2 mg/1 respectively for less sensitive species (e.g. roach); whereas for more sensitive taxa (e.g. salmonids) these levels should be 9 mg/1 and 5 mg/1, respectively (Alabaster and Lloyd 1980) . Oxygen undersaturation is a common feature of Amazonian lakes and rivers (Melack and Fisher 1983). Surface DO levels below 0.5 mg/1 appear to be a persistent, natural condition in many floodplain lakes for extended periods of the year (Junk et al . 1983). Amazonian fish present an impressive variety of anatomical (lungs, swollen lips, air breathing through the intestine, stomach, gas bladder or skin) , biochemical (multiple hemoglobins) , and behavioral (migration) adaptations to cope with these conditions (Riggs 1979, Junk et al . 1983, Saint-Paul and Soares 1987, Val and Almeida-Val 1995). Even though most of these adaptations have been described in taxa that were not common in sandy beach habitats, small characids and cichlids closely related to those found from sandy beaches can stand extreme hypoxic conditions (partial pressure of dissolved oxygen ranging from 9 to 24 torr or roughly 0.4 to 1.1 mg/1) by breathing near the water surface (Kramer and McClure 1982). It appears that Amazonian fish in general can stand low oxygen concentrations. Although not ideal, DO levels downstream from the dam meet the criteria for the survival of less sensitive fish species, suggesting that reduced fish diversity and abundance downstream from the dam was not related to hypoxic water. Responses of habitat-use groups of 136 fish along the Candeias River reinforces the idea that depressed fish diversity along the lower Jamari River was not related to oxygen undersaturated water, but rather associated with greater and fluctuating discharges throughout the dry season. Hydrological Alterations The water level in the Jamari River downstream from the dam remains approximately 1 m above pre- impoundment levels, but it is unknown how much the water level increased in the Candeias River because its only gauging station is located farther upriver from the studied reach. However, daily cycles in water level associated with fluctuating discharges caused by the dam were detectable during the dry season up to 18 river kilometers upriver from the mouth of the Candeias River. The physical alterations in the shoreline habitats, and sandy beaches in particular, are obvious. Sandy beaches in the lower Jamari and Candeias rivers remained partially submerged during the dry season. Only their upper parts emerged from the water, reducing the availability of shallow, slow current habitats during this time of the year. Furthermore, variable discharges produced daily and weekly fluctuations in water level and water current, which intensified the erosional power of the sediment- free water released by the dam. On five occasions during the late dry season of 1993 and 1994, sandy beaches of the lower Jamari could not be sampled because they had been eroded away. Shallow, slow current habitats were converted to deep, swift waters. 137 Responses of Habitat-use Groups to Hydrological Alterations Changes in sandy beach fish assemblages along the lower Jamari and Candeias River were correlated with the longitudinal attenuation of hydrological alterations. Richness and abundance of habitat generalist species, for example, were depressed near the dam and increased farther downstream in the Jamari River, whereas pelagic fish species richness and abundance were reduced near the mouth of the Candeias River and increased farther upriver. River regulation had dramatic effects on richness and abundance of pelagic and benthic species of the lower Jamari River. These groups of fluvial specialist species were poorly represented and did not show any evident signs of spatial recovery along the studied reach. On the other hand, abundance and richness of habitat generalist species were not affected by known alterations in the physical environment of the Candeias River, whereas trends in benthic species abundance suggested that this group was affected. Finally, habitat-use groups of fish from the free-flowing Jaci-Parana River did not show any significant change in richness and abundance along the studied reach, although it is possible that the entrance of two major tributaries along the studied reach may have contributed to a downstream trend of increasing richness and abundance of pelagic fish. Small Fish Responses to Regulation, Comparing Two Case-studies Kinsolving and Bain (1993) showed that components of shoreline fish assemblages had distinct responses to artificial flow fluctuation downstream from a hydroelectric dam: habitat generalist species richness and abundance where unaltered, whereas fluvial specialist species showed 138 an increase in richness and abundance along a 66 km long study reach. They argued that species with broad habitat requirements would cope better with habitat alterations brought about by river regulation than species with narrow habitat requirements. The results from the present study agree with the concept that eurytopic species are better adapted to overcome environmental modifications associated with river regulation than stenotopic species, but it also shows that even eurytopic species richness and abundance can be depressed downstream from hydroelectric dams . Ignoring limitations of comparing studies that used different sampling methodologies and design and that examined very distinct fish faunas, it appears that the sandy beach fish fauna of the Jamari River suffered relatively greater impact due to river regulation than the shoreline fish fauna of the river (Tallapoosa River, Alabama, USA) studied by Kinsolving and Bain (1993). For example, whereas habitat generalists of the Jamari River displayed recovery responses along the studied reach, those from the Tallapoosa River were not affected by river regulation. Furthermore, fluvial specialist species richness and abundance remained depressed along the studied reach of the Jamari River, whereas this group showed a well defined recovery pattern along the Tallapoosa. Besides diverging in the magnitude of responses shown by shallow water assemblages, the Jamari and the Tallapoosa River differed in the intensity of hydrological alterations associated with regulated flows. Daily discharges on the Jamari River ranged between 170 to 240 mVsec during the dry season producing daily variation in water level of 0.4 m on average near the dam, whereas discharges in the Tallapoosa ranged 139 between 0 and 23 0 m3/sec producing daily variation in water level of 2.5 m at a site located 12 km downstream from the dam. These differences are a consequence of distinct operational procedures by each dam (the Samuel Dam on the Jamari has a continuous electricity output that is increased during the evening hours whereas the Thurlow Dam on the Tallapoosa alternates periods of production and shut-down) . The relatively benign conditions in the Jamari when compared with the other regulated river nonetheless caused a much stronger effect on the small fish fauna. Evidence from other studies indicate that predation might be the underlying mechanism involved on the distinct responses of shoreline fish from the Jamari and Tallapoosa rivers. Shoreline habitats have an important function as refuge against predators for fish species that use shallow and slow-current habitats (Bain et al . 1988). Studies have shown the effective pressure that piscivorous fish exert on small fish, forcing them to occupy shallow areas in streams (Power 1984a, Schlosser 1987, Grossman et al . 1987, Mclvor and Odum 1988), and that predation may be responsible for naturally disrupted distribution of small fish in river basins (Fraser et al . 1995). It appears that predator-prey interactions mediated by different operational procedures by the Samuel and Thurlow dams are responsible for the distinct responses observed in habitat-use groups. The Samuel Dam, by maintaining elevated discharges throughout the dry season, has nearly eliminated shallow shoreline habitats (refuges) along the lower Jamari River (and the lower reaches of the Candeias River) . In contrast, rapid decrease in discharge downstream from dams create isolated puddles that contain small fish (Kroger 1973) and small fish species specialized in shallow habitats (Bain et al . 1988). So, the 140 Tallapoosa River, even though subjected to extreme fluctuations in discharges, likely provided temporary shallow water refuges for small size fish during its daily shutdowns. Peaking discharges during the evening hours also contributed to lessening the functional role of remaining shallow habitats of the Jamari as refuge for small size fish, in a similar fashion as that reported for depositional bank refugia in tidal streams (Mclvor and Odum 1988) . Finally, predation risk for small- size fish in the Jamari River likely increased after regulation because the density of medium to large-sized fish that inhabit river channels, as evidenced by gill net sampling before and after dam construction, increased 4-fold immediately downstream from the dam to 2-fold in river reaches farther downstream (Chapter 3). Predation, Colonization, and Habitat-use Group Responses to the Regulation of the Jamari River The regulation of the Jamari River resulted in erosion of shallow sandy beach habitats, and the creation of a system with reduced structural barriers between predator and their prey fishes. The responses of habitat-use groups of fishes in this river might, therefore, have also been related to the ability of small fish to perceive and escape from piscivorous fish, and to successfully colonize open habitats. Cichlid species, for example, were the main component of the habitat generalist group in all studied rivers, and they were more abundant on the lower Jamari River. Besides having broad habitat requirements, cichlids are also known for displaying a wide variety of behavioral adaptations associated with parental care (e.g. nest building 141 and guarding, mouth brooding) , adaptations that favor the ability of young fish to escape from predation. Mouth-brooding Geophagus spp. were more frequently captured on sandy beaches of the lower Jamari River than in the other rivers (pers . observation). In addition to parental care, cichlid species have protracted reproduction, implying that adult cichlids were continuously producing young fish and replacing those lost to predators and environmental stress. Parental care and protracted reproduction might have been fundamental to the observed recovery and abundance of habitat generalist species downstream from the Samuel Dam. Kinsolving and Bain (1993) proposed that colonization was the mechanism determining the recovery pattern of fluvial specialist species along the Tallapoosa River. This mechanism does not appear to be important in the recovery responses of habitat generalist species along the lower Jamari because adult Geophagus spp. are highly associated with deeper portions of sandy beaches. However, colonization is the most likely mechanism explaining the occurrence of pelagic and benthic fish species downstream from the dam. The sandy beaches that yielded the greatest numbers of pelagic fish (Jl and J6) were also fairly close (< 3 river kilometers) to small but perennial, adventitious streams. Likewise, beaches J3 , J4 and J5 were not far from rivulets (apparently backwater outlets) that in most cases stopped flowing by the middle dry season. Sporadic, large schools of pelagic fish (mostly Moenkhausia lepidura) captured from the lower Jamari beaches may have originated from these creeks and backwater outlets. Colonization by sandy beach benthic species, however, does not appear to be as effective and dynamic as in the case of pelagic species. 142 Only two individuals (and two species) of the 17 benthic fish captured in the lower Jamari during this study can be considered as typical of sandy shallow habitats. Stegophilus sp . , a trichomycterid catfish, appears to burrow in the sand (but some species that belong to this genus are also parasites living in the gill chamber of larger catfishes, Burgess 1989). The other species was a banjo catfish (Bunocephalus sp.)( which was always found in sandy beaches with patches of decaying vegetation (leaves, twigs, etc.). Pimelodus spp. constituted the remaining benthic fish captured (15 individuals), but Pimelodus was typically found in deeper waters (it is a medium-sized fish, i.e. > 10 cm standard length) and its occurrence from sandy beaches of the lower Jamari River indicates degradation rather than quality of these shoreline habitats. Such a scant occurrence suggests that benthic fish species are less suited as colonists than pelagic fish species, and that a variety of factors (e.g. different swimming ability, dependence on allochthonous vs. autochthonous food supplies, and differential ability to escape from predation) might be involved. Loricariids, for example, are a very diverse group of benthic fish found in sandy beach habitats of the study rivers except on the lower Jamari. Most loricariids are poor swimmers (Burgess 1989), a factor that would restrict the ability of these catfishes to disperse and colonize open habitats. In addition, experiments with marked fish have shown that although some loricariids are capable of exploring stream reaches nearly 1000 m long, they almost always return to the places from where they left (Power 1984b). Homing responses, if widespread among loricariids, would restrict their capability as colonists even further. As with 143 loricariids, other bottom-dwelling taxa with heavy armored bodies such as aspredinids might have limited swimming capabilities. Colonization Success Once having reached a new place, colonization success will depend largely on the reliability and availability of food sources, and on the ability of newcomers to escape from predation. Benthic feeding activity might increase the susceptibility to detection by predators (Schlosser 1987). On the other hand, available information on the diet of sandy beach species of the study area (Santos 1991) complemented with food habit studies of similar taxa studied elsewhere in the Amazon (Saul 1975, Goulding et al . 1988, Taphorn 1992, Silva 1993) and other neotropical areas (Angermeier and Karr 1983), plus general accounts for closely related taxa (Roberts 1974, Burgess 1989, Moller 1995), indicate that pelagic and benthic taxa differ in the degree of diet specialization and dependence on external (terrestrial) versus internal (aquatic) food sources. Pelagic species depend largely on external food sources, and in many cases terrestrial insects and soft parts of terrestrial plants account for the bulk of what is ingested. In contrast, benthic species feed largely on detritus or algae (Parodontinae, Curimatidae, Loricariidae, Aspredinidae) or on aquatic invertebrates (Characidiidae, Rhamphichthyidae, Callichthyidae) . Dams located in the lower reach of rivers, such as the Samuel Dam, are hypothesized to have little effect on organic matter dynamics (Ward and Stanford 1983) because most organic matter is transported as fine particulate organic matter due to coarse particulate organic matter processing along the river continuum (Vannote et al . 1980). Water released by the Samuel Dam in the lower Jamari transports large amounts 144 of a flocculent material that possibly originates from the decomposition of drowned vegetation within the reservoir (pers . observation). This material, however, does not settle on the sandy beaches, and deposits of vegetation debris are less common than on sandy beaches elsewhere. Apparently, greater and fluctuating discharges downstream from the dam wash this material away from the sandy beaches of the lower Jamari . Fluctuating discharges sometimes can reduce abundance of aquatic invertebrates downstream from hydroelectric dams (reviewed by Petts 1984) , but in some cases other factors known as determinants of invertebrate abundance (e.g. temperature) are also involved. This study did not evaluate aquatic invertebrate responses to regulation, but on several occasions mayfly swarms were observed in the lower Jamari River (pers. observation). Yet, abundance itself does not mean that the resource will be available for consumers, particularly in isolated remnants of sandy beaches. The spectrum of environmental alterations associated with river regulation by hydroelectric dams most likely had stronger effects on those fish species that depend largely on internal, within-river food sources, reducing their capability as colonists. Prospects for the Small Fish Fauna of the Jamari River This study showed that small fish species of the lower Jamari River nearly disappeared from a 40 km reach that extends from the dam to the confluence of the Jamari and Candeias rivers, and that the negative effects of the regulation of the Jamari River propagated to the lower reaches of this tributary. There is, however, an increasing recovery potential with increasing distance from the dam. On the other hand, the Jamari River course downstream from the confluence with the Candeias 145 assumes a more straight shape. Meandering reaches reappear only near its mouth on the Madeira River. Sandy beaches typically appear in the internal, depositional bank of meanders suggesting that this section of the river has a lower potential for sandy beach development, and consequently a scattered and species-poor small fish fauna that is under increasing influence of that of the Madeira River. The upper Jamari and Candeias rivers, potential refuges for the small fish fauna, have been mildly to severely deforested for agriculture and cattle ranching, a process that is still under way. The prospect for the long term preservation of the resident, small fish fauna of the Jamari-Candeias system are clearly not favorable. An inspection of the list of species identified by this study suggests that several components of the small fish fauna found in the studied tributaries of the Madeira River are widespread throughout the Amazon. Yet, our limited knowledge on the taxonomy of this species-rich fauna advises caution when assuming that fish species recorded in the Jamari River can be found elsewhere. This study was not intended as a taxonomic survey of upper Madeira River tributaries, and several named species are in fact species complexes. Taxonomically-oriented studies (e.g. Taphorn 1992) that faced the challenge of identifying the fish fauna of poorly explored areas of the Amazon, are full of remarks concerning the actual status of several "identified species". Therefore, the occurrence of a given species name in the studied rivers does not necessarily mean that it is the same species in the biological sense. Moenkhausia lepidura for example, might include two slightly different forms, one that occurs in the lower Jamari and Candeias rivers, and another present in the upper Jamari and Jaci-Parana. This study makes 146 clear that hydroelectric development of the Amazon can cause, at minimum, local species extinctions of a poorly known small-fish fauna. The spectrum of deleterious effects associated with river regulation on the small fish fauna, as shown in the lower Jamari River, warrants that greater attention be given to these fishes when planning, building and operating hydroelectric dams. River channel assemblages (i.e. large fish species) did not seem to have been as severely impacted by hydroelectric development in the Jamari River, possibly because many components do not reside permanently in the river and their reproduction and early developmental phases take place elsewhere (Chapter 3) . However, apart from their evident sensitivity to river regulation, we know nearly nothing about the requirements of small fish taxa for the completion of their life cycles. A immediate strategy for preserving these species downstream from the Samuel Dam would require the introduction of changes in the operation of the dam during the dry season. Unfortunately , this strategy is not feasible, at least in the short-term, because there is no alternative source of electricity to compensate for a reduction on the energy output by the dam, which would be necessary in order to reduce water levels downstream (Chapter 2) . A long-term strategy would require, however, an expansion of our knowledge on the identity, distribution, habitat use, and life-history requirements of the small fish fauna, and on the maintenance of adequate habitats elsewhere in the basin. CHAPTER 5 FISH MIGRATION, DAM CONSTRUCTION, AND MERCURY CONTAMINATION IN THE MADEIRA RIVER BASIN Introduction Mercury contamination due to gold mining has been recognized as a major environmental problem and health hazard in the Brazilian Amazon. Over 1.2 million people are involved in gold prospecting throughout the region, and estimates suggest that 90-120 tons of mercury are released annually into the environment (Pfeiffer and Lacerda 1988, Lacerda and Salomons 1991). Reports of mercury-contaminated fish date back to the late 1980's in the Madeira River (Martinelli et al . 1988), one of the main centers of gold mining operations . The presence of mercury- tainted fish has been reported at distances up to 180 km downstream from the gold mining area of the Madeira River (Malm et al. 1990), and up to 400 km downstream in the Tapaj6s River, another gold mining center in the Amazon (Malm et al . 1995). Elevated mercury levels found in hair, blood, and urine samples of people living in fishing villages as much as 800 km downstream from gold mining areas have been associated with the consumption of mercury- tainted fish (Malm 1991, Aks et al . 1995). Several processes have been proposed to explain the presence of elevated mercury concentrations in fish and people in areas distant from gold mining operations. Veiga et al . (1994), for example, estimated that significant amounts of mercury, which exists naturally in plant tissues, were released into the Amazon environment by the widespread cutting and 147 148 burning of rainforests. On the other depressed in sandy beaches along the Jamari River hand, Nriagu (1994) proposed that significant mercury fluxes detected in parts of South America were the result of past silver and gold mining operations during colonial times. In the case of the Madeira River, the presence of mercury-contaminated fish and people in areas far downstream from mining sites may be explained by the transport of particulate mercury and mercury dissolved in the water (Nriagu et al . 1992) . Even though fish migration has been mentioned as a possible cause for the presence of mercury- tainted fish in remote areas in the Brazilian Pantanal wetlands (Hylander et al . 1994), or as a possible mechanism of methylmercury transport between tributaries of the Madeira River and the main river (Malm et al. 1990), the importance of fish migrations for the dispersal of mercury pollution in the Amazon has not been reported. Goulding (1980) described several migratory movements of fish from the Madeira River associated with spawning, feeding, and dispersal events. His migratory scheme for large, commercially important characoid fish species (those that form large schools when migrating) involves major exchanges of fish between the main river and its tributaries. During spawning movements, for example, fish move downstream to the mouth of tributaries to reproduce. Dispersal includes movements out of tributaries, upstream in the main river, and reentrance into the next tributary. If fish migration is a mechanism of mercury transport in the Amazon, mercury-contaminated fish should be present in rivers not exposed to gold mining operations. In addition, evidence from studies throughout the world have identified an important primary effect of dam construction: the remobilization of mercury in recently-flooded 149 reservoirs and its assimilation by fish (Rosemberg et al . 1995). Because mercury remobilized in reservoirs is exported to downstream reaches (Aula et al . 1995, Meuleman et al . 1995), fish found downstream from dams in tributaries of mercury-polluted rivers such as the Madeira River can have even higher levels of mercury. In this chapter I report on results of a survey of mercury concentrations in fishes from tributaries of the Madeira River that have no documented history of gold mining activities. I also compare published records of mercury levels in fish from the mercury-polluted Madeira River (Malm 1991, Reuther 1994) to records gathered during this study to evaluate the extent of mercury contamination in the Madeira River basin. In addition, I test the hypothesis that the presence of a hydroelectric power plant in one of these tributaries has intensified mercury concentrations in fishes downstream from the dam. Material and Methods Study Rivers The study was carried out in the Jamari, Candeias, and Jaci-Parana rivers, which belong to the Madeira River basin in the northwestern Brazilian Amazon. The Jamari and Jaci-Parana rivers are tributaries of the Madeira River, whereas the Candeias River joins the Jamari River approximately 40 river kilometers upstream from its confluence with the Madeira River (Figure 2-1). During floods, the Candeias and Madeira rivers are connected through a 10 m wide man-made channel. The Jamari, Candeias, and Jaci-Parana waters are slightly acidic, with low ion content (Table 2-1), which characterize them as Clearwater rivers 150 according to the classification of Sioli (1984). Additional information on water physico-chemical characteristics of these rivers is provided in Chapter 2 . Basin-wide, the Jamari and Candeias rivers have been mildly to severely impacted by deforestation, whereas the Jaci-Parana drainage retains most of its original vegetation. In 1988, the Samuel hydroelectric dam began operation on the Jamari River. Its reservoir flooded 560 km2 of tropical rainforest. The formation of this reservoir, coupled with hypolimnetic release by the dam, reduced oxygen levels significantly in river waters downstream from the dam (Chapter 2) . Before impoundment, the Jamari River was considered a reference for background levels of mercury in fish from the Madeira River basin (Malm et al. 1990). However, by 1991, mercury-contaminated fishes were present in the newly formed reservoir, and in river reaches upstream and immediately downstream from the dam (Reuther 1994) . Fish Collection and Mercury Determination Fish sampling sites in the Jamari River were distributed over approximately 3 5 river kilometers downstream from the dam. Sample sites on the other two tributaries were located along equivalent lengths of river, and there were no obstacles to fish movements between sampling sites and the Madeira River. Fish used for mercury determinations were collected using gill nets during three seasons: May-June, August- September, and October-November of 1994. After collection, the fish were immediately stored in Styrofoam coolers containing ice, transported to the laboratory, and deep-frozen until the field season was completed. Logistical constraints such as 151 isolated sampling sites required that fish remained in the coolers sometimes for an extended period of time during the field work. For the Candeias, Jamari, and Jaci-Parana rivers, this period ranged from two to six days, one to three days, and one to four days, respectively. The fish were kept cool during the entire duration of the field work. Coolers were periodically drained to remove melted water and refilled with ice, in order to maintain proper preservation of fish. In the laboratory, the deep-frozen fish were left to thaw at air temperature, identified to species using a key compiled by Santos (1991), weighed (to the nearest 0.1 g) and measured (standard length to the nearest 0.1 cm). Axial muscle samples were then excised (30-70 g removed from the pre-dorsal area), packed in labeled plastic bags, and returned to the freezer. Mercury determinations were carried out by the Eduardo Penna Franca Radioisotope Laboratory, Rio de Janeiro Federal University, Rio de Janeiro, Brazil. Frozen samples were shipped overnight in insulated containers from Rondonia to Rio de Janeiro. All shipments arrived well preserved (Dr. Olaf Malm, personal communication). The procedure used for mercury determination in fish by this laboratory has been described elsewhere (Malm et al . 1989, Malm et al . 1990). Briefly, analytical determinations of total mercury were performed on triplicate subsamples by cold vapor atomic absorption spectrophotometry. The equipment used included a cold vapor mercury generator accessory (Varian VGA-76) coupled with an atomic absorption spectrophotometer (Varian 1474) . Quality control of the analytical procedures in this laboratory is routinely performed through intercalibration exercises with several reference laboratories (Department of Environmental Medicine, Odense 152 University, Denmark; National Institute of Minamata Disease, Minamata, Japan; and Limnologiska Institutet - Upsala University, Upsala, Sweden) . The Eduardo Penna Franca Radioisotope Laboratory also uses standard samples provided by the reference laboratories as part of its analytical routine (Dr. Olaf Malm, personal communication). Published records of mercury concentration in fish from the Madeira River (Malm 1991, Reuther 1994) used for comparisons with data gathered here were determined using the same analytical procedure. Data Analysis Comparisons of Mercury Concentrations in Fish from the Madeira River and Its Tributaries ~~ To evaluate the extent of mercury contamination in the Madeira River basin I tested for differences between mercury concentrations in fish from the gold mining- impacted Madeira River and fish from its nonimpacted tributaries. Records from Malm (1991) and Reuther (1994), collected during the peak of the gold rush (1987-1991), provided information on mercury levels in fish from the Madeira River. Fish used in these studies were collected in several locations between Porto Velho, Rondonia (immediately downstream from the main gold mining area) to Manicore, Amazonas (over 500 km downstream from Porto Velho) . Because of the broad spatial distribution of sampling sites and reduced sample sizes I pooled records from the Madeira River. Similar limitation required pooling of data from tributaries. Malm (1991), and possibly Reuther (1994), derived scientific names for the fish specimens they studied based on common names given by local fishermen. The use of common names for such purposes can be misleading 153 because the same name can be used for more than one species and one species can be called by different names in different places. Given these uncertainties regarding the identification of species, I carried out comparisons using broad taxonomic units (families and genera, depending on the particular group involved and my personal experience with the usage of common names of fish by the local people) . Only mercury records of taxa common to all data sets were used for comparison. Since mercury concentrations tend to increase with fish growth (e.g. Lange et al . 1994), these records were also inspected using simple linear regressions for the presence of any significant relationship between loglO (mercury concentration) and loglO( fresh weight) . Because no significant relationships were detected, differences in mean mercury concentrations between fish from the Madeira and its tributaries were investigated using t-tests. A similar procedure (t- test) was also employed to control for differences in mean weight of fish between the main river and its tributaries. Comparisons of Mercury Concentrations in Fish Species from the Hydroelectric-developed Jamari River and Two Free-flowing Rivers Comparative studies involving fish species in the Amazon face the task of dealing with enormously high diversity. Estimates of the number of fish species are close to 3000, many of which are still undescribed (Geisler et al . 1975, Goulding 1980). Previous knowledge of the fish fauna of the Jamari, Candeias, and Jaci-Parana rivers allowed the selection of several species common to the rivers. However, many species known to be present in these rivers were not captured during the three field surveys or, if collected, their sizes were under the limit used in this study (approximately 3 0 cm standard length for piscivorous and 20 154 cm for non-piscivorous species), reducing considerably the number of species that could be used for comparisons of mercury among the rivers. Only species that had three or more records per river were used for comparisons . Prior to testing for differences among rivers, all available samples (i.e. a given species in a given river) were inspected for the presence of any significant relationship between loglO (mercury concentration) and loglO (standard length). When there was no significant linear relationship between mercury level and standard length, differences in mean mercury concentration for a given species and among rivers were tested using ANOVA . When a significant relationship between loglO (mercury concentration) and loglO (standard length) was detected, mean mercury concentration was adjusted to a standard size and compared among rivers using 95% confidence intervals. Results A total of 231 fish from tributaries of the Madeira River were examined for mercury concentration in this study. Of these, 140 (60.6 %) had mercury concentrations above 0.5 ug/g, the limit established by Brazil (Brasil 1975) and other countries (e.g. USA, McKim et al . 1976; Canada, Bodaly et al . 1984a) as safe for human consumption. Most samples (175) were from piscivorous fishes, and 77% of these samples were above 0.5 ug/g (Figure 5-1). All three planktivorous fish samples had mercury concentrations above the limit, whereas mercury concentrations in detritivorous, herbivorous and omnivorous fish were in all cases but one under 0.5 ug/g. 155 20 30 40 50 60 70 Standard length (cm) Figure 5-1: Scatterplot of mercury concentration in relation to standard length in fish from three tributaries of the Madeira River. Symbols represent fish feeding habits (inverted triangle = detritivorous fish, diamond = herbivorous fish, triangle = omnivorous fish, square = planktivorous fish, and circle = piscivorous fish) . Line across figure indicates the limit of mercury concentration in fish meat acceptable for human consumption (0.5 ^ig/g) adopted by the Brazilian Health Ministry (Brasil 1975) . 156 Comparisons of Mercury Concentrations in Fish from the Madeira River and Its Tributaries Eight distinct taxonomic groups were common to the three data sets used in this analysis (Malm 1991, Reuther 1994, and the present study), totaling 74 records from piscivorous, herbivorous, omnivorous, and detritivorous fish. There were no significant differences between mean mercury concentrations in taxonomic groups of fish from the Madeira River and its tributaries (Table 5-1). Only Pellona spp. (common name: "apapa") showed a marginally significant and greater mean mercury concentration in the Madeira River. However, weight of fish from the Madeira River was significantly higher than the weight of fish from the tributaries (Table 5-1), suggesting that the known phenomenon of mercury accumulation with the growth of fish may have confounded this comparison. Piscivorous fish from the Madeira and its tributaries had higher mercury concentrations than herbivorous, omnivorous and detritivorous fish. Comparisons of Mercury Concentrations in Fish Species from the Hydroelectric-developed Jamari River and Two Free- flowing Rivers Only four species were captured in sufficient numbers to test for differences in mercury levels among the three study rivers: Hydrolycus scomberoides (common name: "pirandira" ) , Pellona castelnaeana (common name: " apapa -amar el o" ) , Cichla monoculus (common name: "tucunare" or peacock-bass) and Rhaphiodon vulpinus (common name: "peixe-cachorro" or "facao"). These species were among the most common large piscivorous fishes found in the rivers. 157 JB t O <-r. Z Vi Z on Z on Z on z on z on on on Z Z Z oo CI b Z on Z On 00 Z Z On Z on z oo on on z z z I/: s p 60 Q on S S Q on +) 60 X b b OC «/-> d b +i +! + 1 c on NO cn ci d d tN ON o 1*; IT) oo © d d in 1 — ' ^ — - NO CI m NC r— ?; ,77±0 0+68 © c c o +1 C NO +1 On ON O c O d o — rt d d O d +1 BO CI o cj o (N o b d +1 NO ci o eg d in c 8 ?; 3 d +i On On CI d +1 ON ci d 3 CI o +1 oc On ci = 8 8 b d b 00 NO 2 ON o > 2 a 'C 2 OC 0 on +1 s B Q on +1 00 IN oc NC in d d rN' d +1 +i +1 +1 +i re, rN On nC re, q d ri d CI Tf nC rN r-i ON >» re, "* d o pw DC ON © rN re, rN re, d d d d d * — V * — - re i — < ci N — - (14) tN oc oc o 00 ce> .26±0 1 NC IT) 0+06 ,42±0 73±0, O o c o rN d +1 o rN d 5 d rN o NO NO i rN O d +1 On re, d rN d O d © ?! oc d +1 oc C 55 O ?l rN rN d +1 o o rN d s d r- © ?; oc 5 rN d +i © c 3 b NO o fi o ■a i 3 > c. S g e - — . a. c 5 a c on f a. o > c 1 S o o I c > •a i Q 2 u 1 I B > i a 158 R. vulpinus was the only species that showed a significant relationship between mercury concentration and fish length (P=0.03, R=0.48), but only in the Jamari River. Figure 5-2 shows mean mercury concentration for this species in the Jamari, Candeias, and Jaci-Parana rivers (the mean for the Jamari River corresponds to a 45 cm standard length fish, mean standard length for the fish from the Candeias and Jaci-Parana rivers were 45.3 ± 3.0 and 44.9 ± 2.4, respectively). R . vulpinus from the Candeias and the Jamari River tended to have greater mean mercury concentration, but 95% confidence intervals overlapped among rivers. T — l r Jamari Candeias J.Parana Figure 5-2: Mean mercury concentration (± 95% confidence intervals) in Rhaphiodon vulpinus in the three study rivers. Mean for the Jamari adjusted to a 45 cm standard length fish. Numbers above bars are sample sizes . 159 Table 5-2 shows the mean mercury levels for the remaining three species and includes results of analysis of variance and Tukey's multiple comparison procedure. There were significant differences in mean mercury levels in C. monoculus and P. castelnaeana among the three study rivers, c. monoculus from the Jamari River (standard length = 28.7 ± 2.6 cm) had greater mercury concentrations than C. monoculus from the other two rivers (standard length for the Candeias River fish = 29.5 ± 0.5 cm, standard length for the Jaci-Parana fish = 29.0 ± 1.0), whereas P. castelnaeana from the Jamari and Candeias rivers (standard length = 43.4 ± 11.3 cm and 38.9 ± 10.7 cm, respectively) had on average greater mercury levels than P. castelnaeana from the Jaci-Parana River (standard length = 37.1 ± 5.0 cm). As for R . vulpinus, H. scomberoides tended to have greater mean values in the Jamari and in the Candeias rivers, but differences were not significant. Average standard length for this species in the Jamari, Candeias, and Jaci-Parana rivers were 42.2 ± 3.8 cm, 42.4 ± 4.5 cm and 47.7 ± 4.4 cm, respectively. For eight additional species, I could test for differences in mercury concentrations between two rivers. None of these species showed a significant relationship between mercury concentration and standard length, or any significant Table 5-2: Mean mercury concentrations and results of ANOVA and Tukey's multiple comparison procedure for Cichla monoculus, Pellona castelnaeana and Hydrolycus scomberoides from the Jamari ( J) , Candeias (C) , and Jaci- Parana (P) rivers. For the Tukey multiple comparison procedure, letters under the same line do not differ significantly, P=0.05). Species Jamari Candeias Jaci-Parana P-value Tukey C. monoculus P. castelnaeana H. scomberoides 0.77 (n=4) 1.26 (n=9) 0.77 (n=6) 0.41 (n=3) 1.21 (n=7) 0.60 (n=6) 0.40 (n=6) 0.54 (n=6) 0.55 (n=4) 0.0004 0.0017 0.1223 JCP JCP JCP differences in mean mercury concentrations between rivers. Mean, minimum, and maximum mercury concentrations and mean standard length of these species, as well as for the other species that were captured in the study rivers, are presented in Table 5-3. Except for Leporinus friderici, mean mercury concentrations from fishes captured in the Jamari and Candeias rivers were greater than means from the Jaci-Parana, suggesting a trend towards greater mercury levels in fishes from the Jamari -Candeias system. Discussion This study found that mercury contamination is widespread in fish from tributaries of the Madeira River, even though there is no documented history of gold mining in their drainages. Nearly 80% of all piscivorous fish contained mercury levels above the safety limit of 0.5 fig/g adopted by the Brazilian Health Ministry (Brasil 1975) and health organizations of other countries (e.g. US Food and Drug Administration, McKim et al . 1976). Only 35 out of 231 samples of fish (or 15.2%) were under 0.2 ng/g, the background concentration for areas not exposed to gold mining in the Madeira River basin, which was set by mercury concentration in piscivorous fish from the Jamari River collected during the late 1980s (Malm et al . 1990). Thus, mercury concentrations in piscivorous fishes from the Jamari River increased in half a decade from background to levels above those safe for human consumption. 161 Q ir. v. > 5 Q m an X a a s 2 9 « u Q 00 X Q e/j -H -J B S o m c o in d 2 d cm o o NO +1 -H — ON CM oo no cm CM CM t w d cm OV 00 CM CM o o < — i IN 00 d +1 +1 fn — Wl NO — — d — o o o\ r- d d 00 tn VO in 12.2 r*l m o\ o T Is; q ci ~ p*i fi ro 0C 00 SO >» d NO rM — ^ vn fi N N (N if] CM © -r m i> »n — CM — d o d d d OS o © - c o o d d S E 5 s 8 a O g g — d d o d d d +1 >n +j 8 00 in - s s ? 2 S o d d d d d d d odd 53 o 1 CM OS OC q NO NT) rr d co NO q oo CM co r^i fo CM vS cn cn no co ro ro no CM d in CM NO NO On CM CM CM in CM Q CM CM * OC O — NO CM as ro no o rst O OO d CM d d d d d d m CM 5 * >n ro O0 >n >n ol ON o NO 00 d d d d d d d d d d cn ■ — ' cm" r~_ ON OC 5 •r CM m 3 d » T NO NT 00 Q NC c^ in ir; N ON m NO d d d d d d d d d g NV NO • — . en S s NC to r- Q NC C m OC m (S o 5 o c d d o O d d d +1 * OC NO 28± +i i N m in +1 NT, 00± +i T 1 d d 00 d +1 O d O d C5 8 d +H fi o d +1 CM cn oo on CM CM 3 d CM CM +1 CM — s ? CM — On — o — 4H +1 -H Nt N CO PI t OO wS d C*i CM — CM CM CM CM Nt Nf N « m ^ odd g rs d o d +l = q ^ odd _ -H -H -H oo -« n no V CO CM — CM d d c> d d LL. 162 Mercury Sources, Fluxes, and Transport in the Madeira River Basi Pfeiffer and Lacerda (1988) estimated that 55% of the mercury used by gold miners in the Madeira River was released into the atmosphere as Hg° vapor and that 45% entered the river as metallic Hg. An estimated 87 tons of mercury were discharged by the Madeira River gold mining operations between 1979 and 1985 (Lacerda et al . 1989). Of these two potential sources of mercury, only atmospheric transport may be of importance in the study rivers. In some North American remote lakes never exposed to mercury pollution, high levels of mercury in fish has been linked to atmospheric transport and deposition of this pollutant (Sorensen et al . 1990). However, several factors argue against significant atmospheric input of mercury in the three study rivers. First, surveys in gold mining areas along the Madeira River and in Porto Velho's urban area (a gold trading center) have shown that although mercury concentrations in soil and air samples can be extremely high close to gold mining sites and trading shops, they decrease to background levels at short distances from the emission sources (Pfeiffer et al. 1989, Malm et al . 1990, Pfeiffer et al . 1991, Malm et al . 1991). Second, the high humidity in the Amazon accelerates the oxidation of Hg° to Hg*2, which has a short residence time in the atmosphere, and thus is deposited in areas adjacent to where it was emitted (Lacerda et al . 1989) . Finally, wind in Rondonia blows predominately from the south (Serra 1956), which would transport gaseous mercury burnt in gold mining areas along the Madeira River away from the study rivers . Presence of mercury in fish and people in areas distant from gold mining centers in the Amazon may be associated with deforestation because burning of cleared vegetation releases mercury contained in plant tissues (Veiga et al . 1994). Rondonia has gone through an accelerated process of deforestation in the past two decades, loosing 15% of its forests (Stone et al . 1991). However, cleared areas in Rondonia are concentrated in the central and southeastern parts of the state, which includes parts of the Candeias and Jamari systems, but the Jaci-Parana system remains nearly untouched. In the light of the limited significance that atmospheric transport appears to have for dispersal of mercury in the Madeira River basin and considering the results obtained by this study, fish migration is proposed as an alternative mechanism for mercury dispersal in the area. Fish Migrations and Mercury Dispersal The idea of animals acting as dispersers of pollutants is not new. Larsson (1984) showed that organochlorine residues can be exported to terrestrial environments by emerging aquatic insects, and Evans et al . (1987) proposed that shorebirds can transfer heavy metals between estuaries. The installation of fish passages around hydroelectric dams in rivers that drain into the polluted Great Lakes prompted studies to assess the impact that upstream movements of contaminated fishes would have on the wildlife from upper river reaches (Giesy et al . 1994a, 1994b, 1995) . In the case of the Jamari, Candeias, and Jaci-Parana rivers, there were no obstacles to impede the access of fish from the mercury-polluted Madeira River to the study reaches. Furthermore, Goulding (1980) showed that fishes in the Madeira River basin are extremely mobile animals. The movement patterns of fish in the Madeira River basin provides a mechanism for major exchanges of fishes between 164 the main river and its tributaries, and could explain the presence of mercury-contaminated fish in rivers never exposed to gold mining. Fish Migrations in the Madeira River Goulding (1980) studied the biology and ecology of several fish species in the Madeira River basin and reported several migratory movements. From mid-November to January (the early rainy season), fish species migrate from tributaries (such as the study rivers) to the main river. After spawning at the confluence, fishes return to the same tributaries that they came from, and their eggs and larvae drift downstream in the Madeira River. The timing of spawning migration corresponds closely to rising water levels so that by the time they return to the tributaries, they have access to f looded-f orest feeding grounds. From February to mid-March fish remain there, feeding heavily and accumulating fat reserves. When waters start to recede (middle of March), fish move out of the flooded forest back to tributaries, and from there to the Madeira River, which they use as a dispersal route to other tributaries or floodplains located farther upstream. The peak of these upstream dispersal movements in the Madeira River (locally called "piracema" ) extends from August to October. The piracema migration includes another subset of species whose life-history traits are not as tightly linked to the flooded forest, including large catfishes that follow migrating schools to feed on migrating fish. Therefore, it is expected that the completion of migratory species' life cycles encompass long reaches of the Madeira River and its tributaries. Several characoid fish species collected during this study belong to groups identified by Goulding (1980) as undergoing migrations between the main river and its tributaries (e.g. Mylossoma, Triportheus , Leporinus, Prochilodus, and Semaprochilodus) . Catfishes such as Pseudoplatystoma fasciatum, P. tigrinum, Pinirampus pirinampu, Platynematichthys notatus, Sorubimichthys planiceps, Phractocephalus hemioliopterus , Calophysus macropterus and Pseudodoras niger also collected during this study have been observed to move upstream in the Madeira River during piracema migration. Whether catfish species move in and out of tributaries like characoid species could not be determined by Goulding because these species travel close to the bottom, and could only be observed when traversing cataracts along the Madeira River during low water season. Even if these catfish species do not leave tributaries, most of them are piscivores, and by feeding on migratory characoids they can absorb mercury. The exchange of fish between the main river and tributaries would account for the presence of mercury- tainted fish in rivers not directly exposed to gold mining in the Madeira River basin. The comparison of mercury concentrations between fish from the Madeira River (recorded in the literature) and from tributaries (recorded during this study) showed no significant differences between fish from these two general areas, which is compatible with the idea of exchange of fish between the main river and its tributaries. However, the similarity of mean mercury levels between fishes from tributaries and main river, particularly for piscivorous fishes, was unexpected. It would be reasonable to expect a lower concentration of mercury in piscivores from unpolluted tributaries since exposure to sources would be lower, still, the similarity of mean mercury levels between fishes from tributaries and main rivers may be related to fish movements too because sampling sites in unpolluted tributaries were not very far from the mercury-polluted Madeira River (20-60 river kilometers in the Jaci-Parana and 45-80 river kilometers in the Jamari-Candeias system) and fish from the Madeira could enter and exit tributaries more frequently. Besides, it takes from one to three years for mercury concentration in fishes to drop by half (Lockhart et al. 1972, Burrows and Krenkel 1973). If these piscivores eliminate mercury at very low rates, and given the dynamics of fish movements, the time they spend in unpolluted tributaries may not be enough to produce any significant reduction in mercury concentrations. Fish Migrations Elsewhere in the Amazon and Its Implications for Mercury Dispersal * Migration patterns such as the ones described by Goulding (1980) for the Madeira River fish are also present elsewhere in the Amazon River basin. Ribeiro and Petrere (1990) described a migration pattern for the "jaraqui" {Semaprochilodus taeniurus and S. insignis) in the central Amazon (lower Negro and Amazon rivers) that is similar to that of their characoid counterparts of the Madeira River basin. Semaprochilodus spp. from the central Amazon might cover distances of 13 00 km during their annual migrations and as much as 3 00 km during upriver, dispersal migrations. The central Amazon region is an important center of freshwater fisheries that supply Manaus (Bayley and Petrere 1989), the largest city in that part of the Amazon. This area is also located close to the mouths of the Madeira and Tapaj6s rivers in the Amazon River, two centers of gold mining in the region. Records of mercury levels in fish collected close to the mouth of the Madeira River show that by 1986 there were already contaminated fish in that part of the Amazon (Martinelli et al . 1988). Even though fish contamination in the lower 167 Madeira and the central Amazon region can be a consequence of active transport of mercury by rivers (Nriagu et al . 1992), the dispersal of mercury through migrating fish seems to be another important mechanism, extending the threat of mercury contamination to remote, gold mining- free areas of the Amazon. The Samuel Hydroelectric Dam and Mercury Concentrations in Fish from the Jamari River Downstream from the Dam A general trend toward greater mercury levels was observed in several fish species of the Jamari and its tributary, the Candeias River (e.g. Pellona castelnaeana, apapa-amarelo ; Rhaphiodon vulpinus, peixe- cachorro; Hydrolycus scomberoides , pirandira) . Cichla monoculus (tucunare) was the only species that showed significantly higher mercury levels in the regulated Jamari River. The presence of mercury-tainted fish downstream from the dam recorded during this study agrees with findings of Reuther (1994), who reported abnormally high levels of mercury in fish from this location in 1991, three years after the dam started operating. New Reservoirs and Mercury Levels in Fish Downstream from Dams Bioamplif ication and bioaccumulation of mercury in fish has been demonstrated in recently-formed reservoirs that have not been exposed to anthropogenic mercury sources (Potter et al . 1975, Abernarthy and Cumbie 1977, Cox et al. 1979, Reuther 1994). These processes apparently occur very fast in new reservoirs, and are triggered by a combination of factors such as the natural, low-level, occurrence of mercury in inundated soils and enhanced bacterial activity associated with decomposition of abundant flooded organic matter (Cox et al . 1979, 168 Slotton et al . 1987) . Methylmercury, which is formed mainly by the action of decomposing bacteria (Berman and Bartha 1986) , will then accumulate in the reservoir food web (Potter et al . 1975) and can also be absorbed by fish across the gills (Olson et al . 1973). Even though these processes have been identified in reservoirs, the effects may extend farther downstream (Johnston et al . 1991). In the case of the Jamari River, Guimaraes et al . (1995) reported very high potential methylation rates in sediment of a site 500 m downstream from the Samuel Dam. Apparently, the organic-rich sediment produced by decaying vegetation in the reservoir, which is released by the dam, is a substrate for mercury-methylating bacteria in river reaches immediately downstream. Because mercury dissolved in the water of reservoirs and riverine lakes is exported to receiving rivers (Meuleman et al . 1995, Aula et al. 1995), both mercury and conditions favorable to methylation were present downstream from the dam. Results from the comparison of mercury levels in fish among rivers tend to confirm that the Jamari River reach immediately downstream from the dam had intrinsically high methylation rates. Still, certain fish species showed greater mean mercury concentration values in the Candeias River, a tributary of the Jamari. This apparent incongruity might be related, once more, to fish movements . One possibility is that during the peak of the dry season fish moved downstream in the Jamari River and entered the Candeias because of the low oxygen concentration in the water released by the dam (Chapter 3) . A method to test if methylation rates were intrinsically higher in the Jamari River would require comparison of mercury levels using fish species that do not migrate. 169 Cichlids are recognized for their sedentary habits (Bayley and Petrere 1989). The only cichlid species collected in enough numbers to allow comparisons among rivers was cichla monoculus (tucunare). Tucunare was also the only species that showed significantly higher mercury levels in the Jamari River (O.70 ng/g) and relatively similar levels for the Candeias and Jaci-Parana rivers (0.41 and 0.40 jig/g, respectively). Thus, mercury concentrations in tucunare support the concept that mercury methylation rates were intrinsically higher in the Jamari River causing greater mercury concentration in fish, and that movement of fishes confounded the comparison. Mercury levels in tucunare also indicate that cichlids and other sedentary groups of fish are potential indicators of endogenous mercury levels in Amazonian rivers. Dams, Fish, and Mercury in the Amazon Some 100 hydroelectric dams are being planned for the Amazon region of Brazil (Junk and Nunes de Mello 1987), and at the same time gold mining and deforestation are spreading throughout the region (Lacerda and Salomon 1991, Veiga et al . 1994). Bioaccumulation and biomagnification of mercury in new reservoirs are processes that happen independent of anthropogenic mercury inputs. However, reservoirs may also accumulate mercury transported by the atmosphere (Sorensen et al . 1990), which would aggravate the problem. In addition, there is a positive correlation between flooded area and mercury concentration in fish from reservoirs (Johnston et al . 1991). The Samuel reservoir area (560 km2) is small compared with other reservoirs in the Amazon (Tucurui = 2430 km2, Balbina - 2360 km2). The potential synergism among dam construction, gold mining, and deforestation in determining mercury 170 contamination in the Amazonian environment and people deserves greater attention . Even though the focus of this study was in the problem of mercury contamination in the Madeira River basin, a better example of what we might expect in the future can be found elsewhere in the Amazon. The Tucurui hydroelectric dam is located in the Tocantins River, Para state, Brazil. Here, gold mining operations occur in the catchment area of the reservoir (in Serra Pelada and Carajas) as well as downstream from the dam. Large areas in the basin have been cleared for cattle ranching and production of charcoal. Gold mining operations upriver were identified as the main source of mercury that enters the reservoir (550 kg/year) , of which 315 kg/year are exported to the receiving river (Aula et al . 1995) . High levels of mercury were found in fish and people in locations upstream, downstream, and at the reservoir, and the major pathway of mercury assimilation by people was tracked to the ingestion of mercury- tainted fish (Leino and Lodenius 1995, Porvari 1995). Mean mercury concentration in all piscivorous fish species studied in the Tucurui Reservoir were well above 0.5 ng/g (0.95 - 2.9 fig/g) (Porvari 1995) whereas records for mean mercury levels for piscivorous fish species from the Samuel Reservoir range between 0.34 and 0.3 5 \ig/g (0.50 [Lg/g maximum) (Reuther 1994). Such large differences are probably related to the presence of gold mining in the catchment of the Tucurui reservoir and to the larger area flooded by this dam. The operation of the Tucurui dam produced a significant decline in the Tocantins fishery downstream from the dam, estimated as 65% in the two years immediately after the dam started operating. Since then, the stocks of the lower Tocantins basin have not recovered to pre- 171 impoundment levels. At the same time, reservoir fisheries and the fisheries in the middle and upper basin experienced a dramatic increase in catches (315% and 160%, respectively) (Ribeiro et al . 1995). Cichla (tucunare) and Plagioscion ("pescada") accounted for 57% and 21% of reservoir catches in 1988 (estimated in 1424 tons) . Overall mercury levels in the Tucurui area for these piscivorous species ranged between 1.1 and 1.2 ng/g (twice the safe limit for human consumption), and most of the tucunare catches were exported to Belem, the capital of Para (Porvari 1995) . Fisheries in the middle and upper Tocantins are dominated by several detritivorous and omnivorous species, most of which apparently undergo early development in the reservoir and move up to 7 00 km upriver during migration (Ribeiro et al . 1995), transporting mercury in their bodies. One can conclude that the expansion of fisheries in the Tocantins River upstream from the Tucurui Dam is based on the harvesting of mercury- contaminated fish, and demonstrates what we can expect in the future if regulations are not imposed to control the spread of mercury pollution in the Amazon. The construction of dams such as Tucurui or Balbina that flood huge areas is not advisable because of the positive correlation between flooded area and mercury concentration in fish. Predictions that high mercury levels in fish in newly-formed reservoirs was a short-term (3-5 years) phenomenon (Abernarthy and Cumbie 1977, Cox et al . 1979) were, apparently, too optimistic. Morrison and Therien (1995) and Anderson et al. (1995) demonstrated that for omnivorous species (Coregonus clupeaformis , lake whitefish) the return to background levels can take from 8 to 16 years whereas levels in the piscivores Esox lucius 172 (northern pike) and Salvelinus namaycush (lake trout) remained elevated even 21 years after impoundment. Fish are the main source of animal protein for the Amazonian population and fishing is an important economic activity throughout the region (Shrimpton et al . 1979, Smith 1981, Bayley and Petrere 1989, Merona 1990). The ecological, social, and economic implications associated with mercury pollution in this region seems to be disastrous, calling for re-evaluation of hydro-development projects and stricter control of mercury emissions. Despite accumulated evidence that elevated mercury levels in certain fish species from gold mining areas and reservoirs make them unsafe for human consumption, neither state nor federal health authorities have taken any action to warn exposed populations. Fish consumption advisories are unheard of in the Amazon. The degree of fish contamination by mercury in hydroelectric-developed rivers associated with gold mining areas in the Amazon calls for immediate action by health authorities, and the establishment of programs to monitor mercury levels in fish and people. These programs need to consider the likelihood that fish move and transport mercury to areas not directly exposed to mercury contamination. CHAPTER 6 GENERAL CONCLUSIONS AND RECOMMENDATIONS Introduction The starting point for proposing management strategies to mitigate negative consequences of regulation downstream from dams is the identification of underlying or key factors that interfere with system function. This study showed that fish species responses to river regulation were likely a result of modifications in the hydrograph. In addition, this study identified two important dichotomies of fundamental importance to predicting downstream effects of dams upon river fish assemblages. The first dichotomy separates resident from migratory- fish species, whereas the second emphasizes fish size (large vs. small fish). Resident- and small-fish species will suffer greater effects because their life cycles are restricted to the regulated river and modifications in the physical environment affect preferential habitats. Alternatively, migratory- and large-fish species, whose early life- history stages are exported to areas external to the regulated river or to sites distant from areas where stressful conditions occur, are relatively less affected by regulation. Because migratory- and large- fish life cycles encompass broad spatial and temporal scales, their abundance and occurrence in regulated rivers are dependent, to a large degree, on time- lagged conditions of habitats located elsewhere. Thus, strategies to mitigate downstream effects of dams in the Amazon should focus not only on the physical setting of the regulated river, but also 173 174 on links that exist between the regulated river and adjacent river basins. This expanded view of river systems and the necessity of considering broad temporal and spatial scales when studying and managing river systems has been emphasized by Petts et al.(1989) and Schlosser (1991) . A second, and very important point to address before proposing management strategies is how well does the Jamari River represent other Amazonian rivers that will eventually be developed for hydroelectric production? The Jamari River as a Model Most dams proposed for the Amazon will be located in clearwater and blackwater rivers (Junk and Nunes de Mello 1987) . The Jamari River belongs to the first group. These rivers drain either the Brazilian or the Guianean Shields in their upper courses. Waterfalls and rapids appear as shieldian rivers progress towards the Amazon lowlands (Sioli 1984), and these areas of strong relief gradients are potential dam sites. Samuel and Tucurui are examples of dams built on waterfalls and rapids, respectively. Planned dams such as Porteira (Trombetas River in Para) and Paredao (Mucajai River in Roraima) will be located on waterfalls (Ferreira et al . 1988, Ferreira 1993). Shieldian rivers drain old, highly leached terrains. These nutrient-poor rivers are all tributaries of large, nutrient-rich, Whitewater rivers such as the Amazon itself, or the Madeira River. The Jamari River headwaters are located in the western-most portion of the Brazilian shield, and it is a tributary of the Madeira River. This is also the case of the Machado River, where another dam project in 175 Rondonia (Ji-Parana Dam) is in the feasibility study stage (Cadman 1989) . An extensive exchange of fish appears to exist between the nutrient-poor tributaries and the nutrient-rich Whitewater rivers. Reproduction of many commercially important food fishes occurs after downstream migrating fish found in clearwater tributaries reach Whitewater rivers, and their fry undergo early development on adjacent floodplains. Of all Amazonian clearwater and blackwater rivers of which records of reproductive migrations are available, the only exception to downstream reproductive migration is the Tocantins River (Carvalho and Merona 1986). This exception is not surprising since otherwise, eggs, larvae and young fish would end up in the brackish Amazon estuary. Adult migratory food fishes use tributaries such as the Jamari and other nutrient poor rivers as "refueling stops" immediately after spawning, when rising water levels give them access to food resources found in the flooded forests. Therefore, the geological setting determines aquatic productivity that in its turn determines fish migration patterns. These patterns, as previously shown, are important links between regulated (and to-be-regulated) nutrient-poor rivers, and are essential for predicting negative effects of hydroelectric development and proposing management strategies for mitigating these effects. Thus, in broad geological and biological perspectives (as far as fish are concerned) , the Jamari River is representative of an "average" Amazonian river that will potentially be developed for hydroelectric power. 176 Management Strategies for an Amazonian Hydroelectric-developed River If a lesson is to be learned from this study it is that if one is interested in mitigating downstream effects of dams, one should focus or deviations of the altered from the unmodified hydrograph. More precisely, if we are interested in managing river fisheries (i.e. large fish) we should focus attention on both the rising limb and the size of the peak. Alternatively, if we are interested in managing small fish species, we should closely consider changes to its falling limb (Figure 6-1) . The rising limb and peak constitute the flood pulse, and will determine the overall productivity of the river system after regulation, as food fish production, for example. The falling limb, actually its lowest levels, will determine structural suitability of channel margin habitats to small-sized fish species. The present study was conducted while the Samuel Dam was not fully operational. As a result, the maintenance of fishery yield of large fish likely reflected the semi- regulated nature of this river. After the dam became fully operational in 1996, the hydrograph of the Jamari River was modified again. River discharges during the dry season of 1996 were much higher than during interim operation (1988- 1994) meaning that suitability of river channel habitats for small-sized fish would have further deteriorated. Additionally, both the attenuation of the flood peak of 1996 and its shortened duration indicate that the degree of connectivity between the river and its floodplain was severely reduced. Consequently, we can expect a reduction of the productivity of the Jamari River fisheries (measured as yield or standing crop) . In a socio-economical perspective, depression of fishery resources represents a negative impact whereas local extirpation of small-sized fishes is 177 i i i i i 1 1 1 1 1 1 r JASONDJ FMAMJ Month Figure 6-1: Hydrograph of the Jamari River before regulation, during the construction of the dam, and after the dam was finished. Before regulation data based on ELETRONORTE/ SONDOTECNICA (1978) and ELETRONORTE (1994) . During and after regulation data based on unpublished reports by ELETRONORTE ' s Department of Planning and Statistics - CEON. unsound from a conservation perspective. It will be very difficult to make hydroelectric exploitation and conservation of fishery resources compatible under this new scenario. However, there may be alternative measures to mitigate the downstream effects of the Samuel Dam on the Jamari River fisheries and fishes. The modification of the way the dam operates during the dry season could help in the recovery of small-sized fish assemblages (Chapters 2 and 4) . The diminution of floods, however, is a more dramatic effect given its social and economic implications. The proposed strategy to provide shallow habitats for small-sized fishes consists of 178 concentrating electricity production during the rainy season months. To some extent, this procedure is being used by ELETRONORTE (Figure 6-2), but it could be further adjusted to give to the Jamari River a less modified hydrograph. ] Oil-fueled power plants 1 Samuel Dam JFMAMJJASO Month D J Figure 6-2: Electricity consumption in Rond6nia during January 1996 to January 1997. Data from unpublished reports by ELETRONORTE ' s Department of Planning and Statistics - CEON. Considering current electricity consumption in Rondonia, which is on average 100 MW/month (Figure 6-2), it would be necessary to extend the duration of exclusive hydropower generation up to July and to increase river discharges as much as possible during the rainy season, to provide a strong flood pulse. During the dry season (August-October) hydropower output should be reduced as much as possible in order to 179 decrease water levels downstream. To reduce water levels to 53 m above sea level (Figure 6-1), for example, power output by the dam should be reduced to roughly 3 0 MW during the dry season months (Ms. Vania Ferreira, Department of Planning and Statistics, ELETRONORTE, pers . communication) . Unfortunately, installed capacity of oil-fueled power plants (50-56 MW) is not enough to compensate for the required reduction in electricity output by the dam. The amount of electricity required for the immediate implementation of this plan is not much (approximately 20 MW) . However, investments in the electrical sector in Brazil are largely government-sponsored, and given current economic constraints, this plan is not viable. Furthermore, other factors should be considered, as for example the costs of fuel. Increases in oil prices during the 1970s guided energy development strategy in Brazil, and largely justified the expansion of dam construction in the country (Barrow 1988) . A reduction in oil prices during the 1980s slowed down dam building in the Amazon. However, as fossil fuel costs increase, a trend that we can expect in the future, hydroelectric development projects proposed for this region will gain a renewed and definitive momentum (Dr. Nigel Smith, pers. communication). Finally, there is also another important factor to be considered, which is the recognition by decision-makers that the implementation of measures to mitigate environmental impact of dams are as essential as producing electricity. In an analysis of the effectiveness of environmental impact studies of development projects in the Amazon, Santos et al . (1993) pointed out that concern with environmental issues ends when projects are finished. This is very true in the case of dams. 180 Without the interest of decision-makers, chances of implementing measures to mitigate downstream effects of dams are very reduced. Future Perspectives of Hydroelectric Development in the Amazon There are concerns over what the regulation of Amazonian rivers will do to the seasonally inundated floodplains of the Amazon River, Amazon fisheries, and fishes (Bayley 1989, Monosowski 1991, Barthem et al. 1991). This study adds another reason for concern, which is the problem of mercury contamination in hydroelectric-developed river systems, and dispersal of mercury via fish to areas not exposed to mercury pollution. In an analysis of the Tucurui Dam impacts on the Tocantins River fish and fisheries, Leite and Bittencourt (1991) pointed out that current plans for hydroelectric development in this basin should be downgraded because as they are, there will not be adequate habitat left in the river for the completion of life cycles of migratory fish species. Distances of 350-800 kilometers between successive dams have been suggested as necessary to allow reproduction of migratory species (Leite and Bittencourt 1991, Ribeiro et al . 1995). In addition to recommendations about distances between successive dams, the problem of mercury pollution by gold mining should also be considered when planning hydroelectric development in river basins. Areas exposed to mercury pollution should be avoided because the problem of mercury contamination in fish will be exacerbated and may persist for decades. This study showed that hydroelectric dams that are not fully operational do not severely modify the natural flood pulse. River fisheries may, at least, be sustained in tailwaters of these «semi- 181 finished" dams, as long as overexploitation of stocks is not happening. This characteristic of rivers that are not fully regulated can be used as a strategy to mitigate negative impacts of dams on river fisheries. This strategy can be particularly useful in intensively settled riverine floodplains, whose traditional human dwellers depend largely on fishery resources. Changes may occur to species composition of commercial and artisanal catches, as documented by the present fishery study of the Jamari River. Interestingly, these changes reproduce patterns described by Bayley and Petrere (1989) for heavily- fished areas near urban centers of the Amazon. There, species with lower commercial value are replacing high-valued species in commercial catches. Such may be the endpoint eventually reached by tailwater fisheries in the Amazon. Hydropower has been identified as an agent of change for the Amazon region of Brazil because it will foster economic growth and prosperity for its population (Sternberg 1985) . The longer it takes for the fisheries endpoint described above to be reached the better because there is a time lag between the creation of infrastructure and the propagation of economic growth to the impoverished local society. For the traditional populations of the Brazilian Amazon, the only sure thing that they can count on is on the annual rising and falling of waters and on fish, but river regulation may take these both away from them. APPENDIX A FISH SPECIES RECORDED IN THE JAMARI RIVER DRAINAGE IN SELECTED HABITATS LOCATED UPSTREAM (UP) AND DOWNSTREAM (DO) OF THE SAMUEL WATERFALLS BEFORE AND AFTER THE CONSTRUCTION OF THE SAMUEL HYDROELECTRIC DAM Classification Species After Before Channel Channel Lakes Tributaries Artificial . DO UP DO UP DO UP Dp channel Rajiformes Potamotrygonidae Potamotrygon sp. X Osteoglossiformes Osteoglossidae Osteoglossum bicirrhosutn n v J A v A v* X Clupeiformes Clupeidae Pellona castelnaeano. Pellona flavipinnis V #\ V .A Y A Y A Y A Y A A v A Engraulidae Lycengraulis batesii V A V A Y A Characiformes Anns torn iriap nnuSlOfnOlueS lullCtpS Anostomus intermedius Gnathodolus bidens v X X A X X X Laemolyta varia Y A v A v A A X v X Laemolyta laeniata V A V A v X X X X X Leporellus vittatus X Leporinus brunneus X X Leporinus desmotes X X X Leporinus fasciatus X X X X X Leporinus friderici X X X X X X X Leporinus pachycheilus X Leporinus sp. 1 X X X X Leporinus trifasciatus X L. cf. cylindriformis X X X X X Pseudanos gracilis X X Pseudanos trimaculatus X X Rhytiodus argenteofuscus X Rhytiodus microlepis X X Rhytiodus sp. 1 X Schizodon fasciatum X X X X Schizodon vittatum X Characidae Acestrorhynchinae Acestrorhynchus falcirostris X X X Acestrorhynchus heterolepis X Acestrorhynchus falcaltus X X Acestrorhynchus microlepis X X X X X X X Agoniatinae Agoniates anchovia X Aphyocharacinae Aphyocharax anisitzi X 182 183 Classification Species After Before Channel Channel Lakes Tributaries Artificial DO UP DO UP DO UP DO channel Characinae Cheirodontinae Bryconinae Brycon brevicauda Brycon melanopterus Brycon pellegrini Brycon pesu Chalceus macrolepidotus Triportheus angulatus Triportheus albus Triportheus culler Triportheus elongatus Triportheus rotundatus Acestrocephalus sardina Charax gibbosus Heterocharax macrolepis Roeboides thurni Cheirodon notomelas Micro schemobry con cassiquiare Microschemobrycon guaporensis Rhaphiodontinae Hydrolycus pectoralis Hydrolycus scomberoides Hydrolycus sp. 1 Rhaphiodon gibbus Rhaphiodon vulpinus Poptella compressa Astyanax anteroides Astyanax cf. bimaculatus Astyanax guaporensis Astyanax sp. 1 Astyanax zonatus Bryconops alburnoides Bryconops caudomaculatus Bryconops melanurus Creagrutus bolivari Ctenobrycon spilurus Deuterodon acanthogaster Hemigrammus analis Hemigrammus coeruleus Hemigrammus cf. iota Hemigrammus ocellifer Hemigrammus cf. tridens Hemigrammus sp. 1 Hyphessobrycon bentosi Hyphessobrycon callistus lguanodectes geisleri Iguanodectes purusi Knodus heterestes Moenkhausia ceros Moenkhausia collettii Moenkhausia collettii B Stethaprioninae Tetragonopterinae X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X s s s s s s s s s s s X X X X X X X X X X X X X X X X X X X X X X X X XXX X X X X X X X X X X X X X X X 184 Classification Species After Before Channel Channel Lakes Tributaries Artificial DO UP DO UP DO UP DO channel Characidiidae Chilodontidae Ctenoluciidae Curimatidae Erythrinidae Gasteropelecidae Hemiodontidae X X X Tetragonopterinae Moenkhausia comma X Moenkhausia copei X Moenkhausia cotinho X Moenkhausia grandisquamis X Moenkhausia intermedia Moenkhausia lepidura S X X Moenkhausia oligolepis X XX Moenkhausia sp. 2 X Phenacogaster beni X X Tetragonopterus chalceus X X Thayeria obliqua S XXX Characidium catenatum X Characidium fasciatum X Caenotropus labyrinthicus XXX XX Boulengerella maculata X XXX Boulengerella ocellatus X X X X X X Curimata cf. inornata X Curimata knerii X Curimata ocellata XXX Curimata vittata Curimata sp. 1 Curimata roseni X Potamorhina altamazonica X Potamorhina latior X Potamorhina pristigaster Psectrogaster curviventris X Psectrogaster essequibensis X Psectrogaster rutiloides X Curimatella alburna Curimatella meyeri X Curimatopsis macrolepis Cyphocharax cf. microcephalus * X Cyphocharax spilurus * X Steindachnerina fasciata a X Steindachnerina sp. 1 X Erythrinus erythrinus Hoplerythrinus unitaeniatus X X Hoplias malabaricus O X X X X X X Carnegiella marthae Carnegiella strigata Anodus elongatus Anodus sp. 1 Apareiodon sp. 1 X Argonectes scapularis X X Bivibranchia protraclila X Eigenmannina melanopogon X X Hemiodopsis immaculatus X Hemiodopsis microlepis X X XXX X X X X X X X X X X X X X X X X X X X X X X X X X X X X 185 Classification Species After Before Channel Channel Lakes Tributaries Artificial DO UP DO UP DO UP DO channel Hemiodopsis semitaeniatus X X X X Hemiodus unimaculatus X X X X X X X X Hemiodidae sp. 1 X Nannostomus beckfordi s X Nannostomus eques X Nannostomus trifasciatus X Pyrrulina laeta X X Prochilodus cf. beni X X I ) - I ' J J c • • Prochilodus cf. nigricans 0 X X Semaprochilodus taeniurus X Semaprochilodus theraponura X X X X X Catopnon mento X X Colossoma macropomum X X Myleus pacu X X X X X X Myleus sp. 1 X X X X Myleus sp. 2 X X X X X Mylossoma aureum X X Mylossoma duriventre X X X Piaractus brachypomum X Serrasalmus aureus X X Serrasalmus eigenmanni x x Y Y Serrasalmus elongatus X Serrasalmus rhombeus X X X X Serrasalmus striolatus X X Serrasalmus sp. 1 X Serrasalmus sp. 2 X X Serrasalmus sp. 3 X Adontosternarchus sachsi X Apteronotus albifrons 0 X X Apteronotus sp. 1 X Porotergus gymnotus X Sternarchorhynchus oxyrhynchus X Electrophorus electricus X X X X X Gymnotus anguillaris X X Gymnotus carapo X X Hypopomus brevirostris X X Hypopomus sp. 1 Y -lA. Gymnorhamphichthys hypostomus X Rhamphichthys marmoratus X Archolaemus Max X iLigeniuuTinia virescens X X X Rhabdolichops troscheli X Sternopygus macrurus 0 X X Ageneiosus brevifilis X X X X Ageneiosus valenciennesi X Ageneiosus ucayalensis X X Hemiodontidae Lebiasinidae Prochilodontidae Serrasalmidae Gymnotiformes Apteronotidae Electrophoridae Gymnotidae Hypopomidae Rhamphichthyidae Sternopygidae Siluriformes Ageneiosidae 186 Classification Species Before After Channel Channel Lakes Tributaries Artificial DO UP DO UP DO UP DQ channel Ageneiosidae Aspredinidae Auchenipteridae Callichthyidae Cetopsidae Doradidae Helogeneidae Hypophthalmidae Loricariidae Pimelodidae Tetranematichthys quadrifilis Bunocephalus sp. s Auchenipterus nuchalis X Auchenipterichthys thoracatus X Centromochlus heckelii X Parauchenipterus galeatus X Parauchenipterus sp. 1 Tatia sp. 1 Callichthys callichthys b Corydoras caudimaculatus Corydoras gracilis Corydoras schwartzi Hoplosternusm littorale Hoplosternum thoracatum Pseudocetopsis plumbeus Acanthodoras spinosissimus 0 Hassar sp. 1 Hassar sp. 2 Hemidoras sp. x Opsodoras humeralis X Opsodoras stubelii Opsodoras trimaculatus X Platydoras costatus X Pseudodoras niger X Trachydoras sp.l o Helogenes marmoratus Hypophthalmus edeniatus X Hypophthalmus marginatus X Ancistrus sp. 1 Cochliodon sp. 1 Hemiodontichthys acipenserinus X Hypoptopoma gulare Hypoptopoma thoracatum X Hypostomus sp. 1 Hypostomus sp. 2 X Hypostomus sp. 3 Lasiancistrus scolymus Leporacanthicus galaxias Loricaria cataphracta X Oxyropsis carinatus Peckoltia vittata X Pseudorinelepis genibarbis X Pterygoplichthys gibbiceps X Rineloricaria cacerencis Rineloricaria phoxocephala Spatuloricaria evansii Brachyplaty stoma vailantii Calophysus macropterus x X X X X X X X X X X X X X XXX XXX X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X 187 Classification Species Before After Channel Channel Lakes Tributaries Artificial DO UP DO UP DO UP DQ channel Pimelodidae Trichomycteridae Beloniformes Belonidae Synbranchiformes Synbranchidae Perciformes Cichlidae Hemisorubim platyrhynchos Imparfinis sp. 1 Leiarius pictus Megalonema sp. 1 Paulicea lutkeni Phractocephalus hemioliopterus Pinirampus pirinampu Platynematichthys notatus Pseudoplaty stoma fasciatum Pseudoplaty stoma tigrinum Sorubimichthys planiceps Pimelodina flavipinnis Pimelodella cristata Pimelodella sp. 1 Pimelodus albofasciatus Pimelodus blochii Pimelodus ornatus Pimelodus sp. 1 Pseudopimelodus zungaro Rhamdia sp. 1 Rhamdia sp. 2 Sorubim lima Branchioca sp. 1 Paracanthopoma sp. 1 Stegophilus sp. Trichomycterus sp. 1 Pseudotylosurus microps Synbranchus marmoratus Acaronia nassa Aequidens diadema Aequidens syspilus Aequidens tetramerus Aequidens virides Apistogramma pulchra Apistogramma resticulosa Biotodoma cupido Chaetobranchopsis orbicularis Chaetobranchus flavescens Cichla monoculus Cichla temensis Crenicichla johanna Crenicichla lenticulata Crenicichla proteus Crenicichla regani Geophagus cf. proximusc X X X X X X 0 X X X X X X X X X X X X X X X X X X X X 0 X X X X X X X X X X X X X X X X X X X X X X X X s X x x X s X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X 188 Classification Species After Before Channel Channel Lakes Tributaries Artificial Cichlidae CrPn'nhn on c cn 1 X ur ur cnannei X X X nypseiecara temporalis X X X Mesonauta festivus X X X X X Pterophyllum scalare X Satanoperca jurupari v A v A A X X Nandidae Monocirrhus polyacanthus X Sciaenidae Plagioscion squamosissimus X X X Pachypops sp. 1 X X X Pachyurus sp. 1 X Tetraodontiformes Tetraodontidae Colomesus asellus s X Total number of species 148 97 70 36 125 83 39 41 Total number of species recorded in the Jamari River drainage 278 dam records X = 0 = species captured with gill net, s = species captured with seine, species captured with other gear or observed in the field. Note 2: Species name updates and other species-related observations- a ■■ species name updated according to Vari (1991) and Vari (1992a); b = Callichthys callichthys was recorded in a swamp area created by the embankment of a small tributary of the Jamari River; c = distributional records suggest that the Geophagus identified by Santos (1991) as G. surinamensis is possibly G. cf. proximus . Sources: Santos (1991) (records before the construction of the Samuel hydroelectric dam) , and this study (records after construction of the Samuel hydroelectric dam) . APPENDIX B EDITED TWINSPAN* OUTPUT SHOWING CODED ABUNDANCE VALUES FOR 71 FISH SPECIES CAPTURED DURING THE DRY SEASON IN THE JAMARI AND IN THE CANDEIAS RIVER Species Sample code £2^£ C17C26C13C22C23C27C12C16C32C33C36J12 J26 J22 J32 J36 J23 J27 J33 J37 C37 J13 J16 J17 Boulema 2 2 2 2 3 3 1 1 - - ! " I " \ ~_ \ ' " \ | \ — \ Curimar 3 - - 2 3 2 - 2 - 1 1 Cichlat - 3 1 2 1 2 3 2 1 Hemioac 2113---22----2------ Opsohum 222----31-1-... 1 Opsotri 2 1 - 3 3 2 - - 1 2 2- Acesmic 32-2--1---2 Auchtho - 4 - 1 2 2 1 - 1 - 2 Brypesu - 2 2 2 -2 Satanoj 2 - - 2 2 1 2 1 - - - - 1 1 2 - - 1 - - 1 - - 1 - . . Aceshet 12-2123132-- - - 2 1 - - 1 - 1 Bryalbu 321421441--- Centrom 33-42233443 - - - 2 - - - - 5 . . . . . 5 Lycengr 1----112232--- Hemimic 5-1112434---42 Argosca - 1 - - 2 2 - 1 - 1 - - l i Caenotr 5-1114----222- Herossp - - 2 1 i Chalceu 4545342522353241 Geophsu 234543452333433332222 - 2 Sorulim 4422-3352-22-3-2321---1 Hydrosc 2-3111323-14-3313112--- 1 1 1 1 - - 4 1 Hydrosp - - - 2 1 1 1 2 2 2 2-1 Crenile 111- 22212-1-21---1 Piniram - 2- --121211213223---12-2 Serrsp2 -1-2-1 1-2-2---2-1-- Bouleoc 2221--242121124231 121 1 - 2 Serrasr - 3122-222-12-243212222-- Hemidor 4-313--3221-31--421-122- Hemiuni 433313134133421342-23-33 Pimespl 334544345534433132333544 Peckolt - 2 - 1 l Plagios 1 - 1 1 2 2 2 1 Rhaphig - 1 - - l - - i 3 - - - - 2 - - 11-1-223 1 - - - 1 Tripoel 4423343-31-1-25223235 Cichlam 11--2-12-1--1-...2-2- Hypost2 212-331-12--- 11- 211- 2 Myleus2 ---.-.13.2 Steispl 2 - - - 2 - - - 2 2 1 Curimai - - - - 2 1 - - 1 1 1 - - 1 - 3 - - 2 189 190 Specie Sample code C17C26C13C22C23C27C12C16C32C33C36J12 J26 J22 J32 J36 J23 J27 J33 J37 C37 jjj J16 J17 Lepofas - 2 - 3 2 3 - 2 - - 2 - 2 1 4 4 2 - 2 3 2 2 1 2 Semathe - - 2 2 1 - 2 - - - - 3 2 3 2 2 3 2 1 4 - 2 1 - Serrase --- 2 2 1 1 1 1 3 4 1 - 2 3 1 - l Acesfar 2 - - - i 1 1 - 1 - - 1 - 2 1 Laemova - 2 1 - 1 i - . 3 3 1 3 4 2 3 2 5 2 5 4 1 4 2 3 Lepofri 1 - - 2 1 - - 2 2 - 2 - - 2 3 3 1 1 2 2 2 3 - 3 Cunmak 11--1--1-32234-21-12-2S Prochib 2 1 1 1 - - 3 3 1 1 2 2 2 1 3 Lepokla -3-122--] Myloaur - 2 - - 1 3 .... 2 Mylodur 252224-1-32111 Hemisop - - - 1 1 - - 2 2 Platyno - - 3 - - 2 - - - 4 1 - 1----22-312--2 - - - 2 - 2 2 - - 2 3 1 1 5 2 5 5 3 -5 - 1 - - 1 - 1 - - 1 - 3 1 - 1 1 - - 2 - - - Ageneib -2--2---22---311223212- Brymela 1 1 - - 2 - - 1 1 2 - l 1 PeUonc 1 2 - - 1 - 1 1 . 2 3 3 - 2 3 - - 1 Henuima 4 2 - - - 2 5213 12 Pellonf 1--12111-4--1-1. 42324 Pimeloa - - 1 1 - 2 - - 2 1 3 3 2 Pseudni Hydrope 11 2 - Rhaphiv 312-43222313221-55354545 ScMzof - 1 1 1 1 - 2 - - - l ... 2 1 3 2 3 Calophy - - l - . 2 - - 1 1 1 3 2 2 - 2 4 -3 Potamla 4-- .-1-212- 12-- -424355- 4 Pseudpt - - 1 1 ... j Rhytisp 3 4 2 1 - - 1 - - 1 2 2 2 1 2 2 1 1 - - 2 - 1 J"P°aS 2 2 - 1 - 1 - - 4 2 - 3 5 4 - 5 Potamal 1 1 - - 2 - - 2 2 4 - 4 PsCCtrC 1 3--4S-4 PSeCttT „ 1 - - - - - - 2 - - 3 9 - g 1st. level 0 0 0 0 0 0 0 0000000001 1 I J 1 I J f 2nd. level 000000000011iiii0000011i 3rd, level 000000111ioooi1100001 * TWINSPAN is a computer program that constructs two-way tables to classify samples and species by successive dichotomous divisions (Hill 1979) . Raw abundance data used in this classification were coded by the program using default values (1=0-1% of the total number of individuals m the sample, 2=2-4%, 3=5-9%, 4=10-19%, 5=20-100%). Only the ^aS!1^Cati°n °f samPles (sites) produced by the program is shown on the bottom of the table (a), and up to the 3rd level. Samples sharing the same digit rowwise and columnwise have similar internal structure (i.e. similar composition and species abundance patterns). Species code are according to Table 3-3 and site codes are according to Figure 3-18 LIST OF REFERENCES Abernarthy, A. R. and P. M . Cumbie. 1977. Mercury accumulation by largemouth bass (Micropterus salmoides) in recently impounded reservoirs. Bulletin of Environmental Contamination and Technoloov 17:595-602. y Aks, S. E. , T. B. Erickson, F. J. o. Branches and D. O. Hryhorczuk. 1995. Blood-mercury concentrations and renal biomarkers in Amazonian villagers. Ambio 24:103-105. Alabaster, J. s. and R. Lloyd. 1980. Water Quality Criteria for Freshwater Fish. Butterworths . London. U. K. Allan, J. D. 1995. Stream Ecology: Structure an Function of Running Waters. Chapman & Hill. London. England. Anderson, M. R., D. A. Scruton, U. P. Williams, and J. F. Payne. 1995. Mercury in fish in the Smallwood reservoir, Labrador, twenty-one years after impoundment. Water, Air, and Soil Pollution 80:927- 930. Angermeier, P. L. and I . J. Schlosser. 1989. Species-area relationships for stream fishes. Ecology 70:1450-1462. Angermeier, P. L. and J. R. Karr. 1983. Fish communities along environmental gradients in a system of tropical streams. Environmental Biology of Fishes 9:117-135. Arcifa, M. S. and A. J. Meschiatti. 1993. Distribution and feeding ecology of fishes in a Brazilian reservoir: Lake Monte Alegre. Interciencia 18:302-313. Arcifa, M. S., C. G. Froehlich, and S. M. F. Gianesella-Galvao . 1981. Circulation patterns and their influence on physico-chemical and biological conditions in eight reservoirs in Southern Brazil. Verh. Internat. Verein. Limnol. 20:1054-1059. Aula, I., H. Braunschweiler, and I. Malin. 1995. The watershed flux of mercury examined with indicators in the Tucurui reservoir in Para, Brazil. Science of the Total Environment 175:95-107. Ayres, J. M. 1993. As Matas de Varzea do Mamiraua, Medio Rio Solimoes. CNPq and Sociedade Civil Mamiraua. Brazil. Bain, M. B., J. T. Finn, and H. E. Booke. 1988. Streamflow regulation and fish community structure. Ecology 69:382-392. Baker, B. W. and G. L. Wright. 1978. The Murray valley: Its hydrological regime and the effects of water development on the river. Proceedings of the Royal Society of Victoria 90:103-110 191 192 Barbieri, G. 1989. Dinamica da reproducao e crescimento de Hoplias marabaricus (Bloch, 1794) (Osteichthyes , Erythrinidae) da Represa do Monjolinho, Sao Carlos, SP. Revista Brasileira de Zooloqia 6:225-233. Barco, M. V. and M. Z. Vilarreal. Some Ecological aspects and present state of the fishery of the Magdalena River basin, Columbia, South America, pp. 409-421. In: D. P. Dodge [ed.], Proceedings of the International Large River Symposium. Can. Spec. Publ . Fish Aquat Sci. 106. Barrow, c. J. 1987. The environmental impacts of the Tucurui Dam on the middle and lower Tocantins River basin, Brazil. Regulated Rivers 1:49-60. Barrow, C. J. 1988. The impact of hydroelectric development on the Amazonian environment with particular reference to the Tucurui Project. Journal of Biogeography 15:67-78. Barthem, R. B. 1987. Uso de redes de espera no estudo de ritmos circadianos de algumas especies de peixes nos lagos de varzea do Rio SolimSes. Revista Brasileira de Zoologia 3:409-422. Barthem, R. B., M. C. L. B. Ribeiro, and M. Petrere Jr. 1991. Life strategies of some long-distance migratory catfish in relation to hydroelectric dams in the Amazon basin. Biological Conservation 339-345. Bayley, P. B. 1988. Factors affecting growth rates of young tropical floodplain fishes: Seasonality and density dependence. Environmental Biology of Fishes 21:127-142. Bayley, P. B. 1989. Aquatic environments in the Amazon basin, with an analysis of carbon sources, fish production, and yield, pp. 399- 408. In: D.P. Dodge [ed.], Proceedings of the International Large River Symposium. Canadian Special Publication on Fisheries and Aquatic Sciences 106. Bayley, P. B. 1991. The flood pulse advantage and the restoration of river-f loodplain systems. Regulated Rivers 6:75-86. Bayley, P. B. and M. Petrere Jr. 1989. Amazon fisheries: Assessment methods, current status and management options, pp. 385-398. In: D.P. Dodge [ed.], Proceedings of the International Large River Symposium. Canadian Special Publication on Fisheries and Aquatic Sciences 106. Begon, M. , J. L. Harper and C. R. Townsend. 1990. Ecology: Individuals, Populations and Communities. 2nd. edition. Blackwell Scientific Publications. Cambridge. Massachusetts. Berman, M. and R. Bartha. 1986. Levels of chemical versus biological methylation of mercury in sediments. Bulletin of Environmental Contamination and Toxicology 36:401-404. Bodaly, R. A., R. E. Hecky, and R. J. P. Fudge. 1984a. Increases in fish mercury levels in lakes flooded by the Churchill River diversion, Northern Manitoba. Canadian Journal of Fisheries and Aquatic Sciences 41:682-691. 193 Bodaly, R. A.( T. W. D. Johnson, R. J. P. Fudge, and J. w. Clayton. 1984b. Collapse of the lake whitefish (Coregonus clupeaformis) fishery m Southern Indian Lake, Manitoba, following lake impoundment and river diversion. Canadian Journal of Fisheries and Aquatic Sciences 41:692-700. Brasil 1975. Ministerio da Saude, Resolucao Numero 18/75 da Comissao de Normas e Padroes para Alimentos. Diario Oficial da Uniao 9 de dezembro de 1975. Brasil. 1985. Diagnostico dos Recursos Hidricos: Avaliacao do Regime Hidrometereologico do Noroeste do Brasil, Programa POLONOROESTE Ministerio das Minas, Departamento Nacional de Aguas e Energia Eletrica. Brasilia, DF, Brazil. Burgess, W. R. 1989. An Atlas of Freshwater and Marine Catfishes. T. F H. Publications, Inc. Ltd. Neptune City, New Jersey. U. s. A. Burrows, W. C. and P. A. Krenkel. 1973. Studies on uptake and loss of methylmercury-203 by bluegills (Lepomis macrochirus Rafinesgue) Environ. Sci. Technol. 7:11-27-113 0. Cadman^j. D. 1989. Energy from the Amazon. Civil Engineering 59 (12) :54- Cadwallader, P. L. 1978. Some causes of the decline in range and abundance of native fish in the Murray-Darling River system. Proceedings of the Royal Society of Victoria 90:211-224. Carvalho, J. L. and B. Merona. 1986. Estudos sobre do is peixes migrat6rios do baixo Tocantins, antes do fechamento da barragem de Tucurui. Amazoniana 9:595-607. Cassidy, R. A. and P. E. Dunn. 1987. Water temperature control and areal oxygen consumption rates at a new reservoir, and the effects on the release water, pp. 33 9-3 51. In: J. F. Craig and J. B. Kemper [eds.], Regulated Streams: Advances in Ecology. Plenum Press New York. Chauvet, E. and H. Decamps. 1989. Lateral interactions in a fluvial landscape: The River Garonne, France. Journal of the North American Benthological Society 8:9-17. Cox, J. A., J. Carnahan, J. DiNunzio, J. McCoy, and J. Meister. 1979 Source of mercury in fish in new impoundments. Bulletin of Environmental Contamination and Toxicology 23:779-783. Craig, J. F. and J. B. Kemper. 1987. Regulated Streams: Advances in Ecology. Plenum Press. New York. Cushman, R. M. 1985. Review of ecological effects of rapidly varying flows downstream from hydroelectric facilities. North American Journal of Fisheries Management 5:330-339. Delucchi C M 1988. Comparison of community structure among streams 2 Hfren temP°ral flow regimes. Canadian Journal of Zoology oo:b/9-586. 194 Dolan, R., A. Howard, and A. Gallenson. 1974. Man's impact on the Colorado River in the Grand Canyon. American Scientist 62:392-401. ELETRONORTE. 1988. Estudos de Impacto Ambiental (EIA) , v. 2 - Metodologia e diagnostico ambiental. Unpublished Report # SAM-70- 2360-03. Brasilia, DF, Brazil. ELETRONORTE. 1990. Usina Hidroeletrica Samuel. Departamento de Comuni cacao Social, ELETRONORTE. Brasilia, DF, Brazil. ELETRONORTE. 1993. Estacao Ecologica de Samuel, Rondonia, Brasil. Piano de Manejo (Versao Preliminar) . Brasilia, DF, Brazil. ELETRONORTE. 1994. Precipitacao Pluviometrica (mm) e Vazoes Maximas e Minimas. Unpublished Report, ERGS - Setor Tecnico. Porto Velho, Rondonia, Brazil. ELETRONORTE/ SONDOTECNICA. 1976. Relatorio de reconhecimento do local da Usina de Samuel. Brasilia, DF, Brazil. ELETRONORTE/ SONDOTECNICA. 1977. Determinacao da Evaporacao Mensal . Unpublished Report # ELN EG839/V26 . 02377 . Brasilia, DF, Brazil. ELETRONORTE /SONDOTECNICA. 1978. Relatorio da Campanha Hidrosedimentometrica e Climatologica . Unpublished Report # SAM- 10-3177-RE. Brasilia, DF, Brazil. ELETRONORTE/ SONDOTECNICA. 1987. Estudos de meio ambiente: Diagnostico ambiental preliminar - Ictiofauna. Unpublished Report # SAM-70- 2211 RE. Brasilia, DF, Brazil. ELETRONORTE/ SONDOTECNICA. 1989. Derivacao das aguas da bacia do Rio Candeias para a ampliacao da geracao na UHE Samuel. Resumo do Estudo de pre-viabilidade . Unpublished report # SAM-75-1001 RE. Brasilia, DF, Brazil. Evans, P. R.( J. D. Uttley, N. C. Davidson, and P. Ward. 1987. Shorebirds (S.Os charadrii and Scolopaci) as agents of transfer of heavy metals within and between estuarine ecosystems, pp. 337-352. In: P. J. Coughtrey, M. H. Martin, and M. H. Unsworth [eds.], Pollutant Transport and Fate in Ecosystems. Blackwell Scientific Publications. U. K. Fearnside, P. M. 1989. A prescription for slowing deforestation in Amazonia. Environment 31:16-40. Ferreira, E. J. G. 1984. A ictiofauna da represa hidreletrica de Curua- Una, Santarem, Para. I - Lista e distribuicao das especies. Amazoniana 8:351-363. Ferreira, E. J. G. 1993. Composicao, distribuicao e aspectos ecologicos da ictiofauna de urn trecho do Rio Trombetas, na area de influencia da futura UHE Cachoeira Porteira, Estado do Para, Brasil. Acta Amazonica 23 (suplemento) : 1-89 . Ferreira, E. J. G., G. M. dos Santos, and M. Jegu. 1988. Aspectos ecologicos da ictiofauna do Rio Mucajai, na area da ilha Paredao, Roraima, Brasil. Amazoniana 10:339-352. 195 Fraser, D. F. , j. F. Gilliam, and T. Yip-Hoi. 1995. Predation as an agent 76:146 agent of population fragmentation in a tropical watershed. Ecology 1-1472. Froehlich, C. G., M. S. Arcifa-Zago, and M. A. J. de Carvalho. 1978. Temperature and oxygen stratification in Americana Reservoir, " State of Sao Paulo, Brazil. Verh. Internat . Verein. Limnol 20 : 1710-1719 . Geisler, R., H. A. Knoppel , and H. Sioli. 1975. The ecology of freshwater fishes in Amazonia, present status and future tasks for research. App. Sci. Develop. 2:144-162. Gelwick, F. P. 1990. Longitudinal and temporal comparisons of riffle and pool fish assemblages in a Northeastern Oklahoma Ozark stream Copeia 1990:1072-1082. Gery, J. 1977. Characoids of the World. T. F. H. Publications, inc. Ltd Neptune City, New Jersey. U. S. A. Giesy, J. P., D. A. Verbrugge, R. A. Othout, W. W. Bowerman, M. A. Mora, P. D. Jones, J. L. Newsted, C. Vandervoort, S. N. Heaton, R. J. Aulerich, S. J. Bursian, J. P. Ludwig, M. Ludwig, G. A. Dawson, T. J. Kubiak, D. A. Best, and D. E. Tillitt. 1994a. Contaminants in fishes from Great Lakes -influenced sections and above dams of three Michigan Rivers. I: Concentrations of organo chlorine insecticides, polychlorinated biphenyls, dioxin equivalents, and mercury. Archives of Environmental Contamination and Toxicology 27:202-212. Giesy, J. P., D. A. Verbrugge, R. A. Othout, W. W. Bowerman, M. A. Mora, P. D. Jones, J. L. Newsted, C. Vandervoort, S. N. Heaton, R. J. Aulerich, S. J. Bursian, J. P. Ludwig, G. A. Dawson, T. J. Kubiak, D. A. Best, and D. E. Tillitt. 1994b. Contaminants in fishes from Great Lakes -influenced sections and above dams of three Michigan Rivers. II: Implications for the health of mink. Archives of Environmental Contamination and Toxicology 27:213-223. Giesy, J. P., w. W. Bowerman, M. A. Mora, D. A. Verbrugge, R. A. othoudt, J. L. Newsted, c. L. Summer, R. J. Aulerich, S. J. Bursian, J. P. Ludwig, G. A. Dawson, T. J. Kubiak, D. A. Best, and D. E. Tillitt. 1995. Contaminants in fishes from Great Lakes- influenced sections and above dams of three Michigan Rivers. Ill: Implications for health of bald-eagles. Archives of Environmental Contamination and Toxicology 29:309-321. Gorman, O. T. and J. R. Karr. 1978. Habitat structure and stream fish communities. Ecology 59:507-515. Gottsberger, G. 1978. Seed dispersal by fish in the inundated regions of Humaita, Amazonia. Biotropica 10:170-183. Goulding, M. 1980. The Fishes and the Forest. University of California Press. Berkeley. Goulding, M. 1981. Man and Fisheries on an Amazon Frontier. Dr. W. Junk Publishers. The Hague. The Netherlands. 196 Goulding, M. , M. L. Carvalho, and E. G. Ferreira. 1988. Rio Negro, Rich Life in Poor Water. SPB Academic Publishing bv. The Hague. The Netherlands . Gribel, R. 1990. The Balbina disaster: The need to ask why? The Ecologist 20:133-135. Grossman, G. D., A. de Sostoa, M. C. Freeman, and J. Lobon-Cervia . 1987. Microhabitat use in a Mediterranean riverine fish assemblage. Oecologia (Berlin) 73:490-500. Guimaraes, J. R. D., o. Malm, and W. c. Pfeiffer. 1995. A simplified radiochemical technique for measurements of net mercury methylation rates in aquatic systems near goldmining areas, Amazon, Brazil. Science of the Total Environment 175:151-162. Gurgel, J. J. s. and C. H. Fernando. 1994. Fisheries in semi-arid Northeast Brazil with special reference to the role of Tilapias. Int. Revue ges . Hydrobiol. 79:77-94. Guy, P. R., 1980. River bank erosion in the mid-Zambezi valley, downstream of Lake Kariba. Biological Conservation 19:199-212. Henderson, P. A. and I. Walker. 1990. Spatial organization and population density of the fish community of the litter banks within a central Amazonian blackwater stream. Journal of Fish Biology 37:401-411. Hill, M. O. 1979. TWINSPAN, a FORTRAN program for arranging multivariate data in an ordered two-way table by classification of the individuals and attributes. Cornell University. Ithaca. New York. Holden, P. B. and C. C. Stalnaker. 1975. Distribution and abundance of mainstream fishes of the Middle and Upper Colorado River basins. Transactions of the North American Fisheries Society 104:217-231. Hylander, L. D., E. C. Silva, L. J. Oliveira, S. A. Silva, E. K. Kuntze, and D. A. Silva. 1994. Mercury levels in Alto Pantanal : A screening study. AMBIO 23:478-484. Ibarra, M. and D. J. Stewart. 1989. Longitudinal zonation of sandy beach fishes in the Napo Basin, Eastern Ecuador. Copeia 1989:364-381. Imevbore, A. M. A. 1967. Hydrology and plankton of Eleiyele Reservoir, Ibadan, Nigeria. Hydrobiologia 30:154-176. Jalon, D. G., P. Sanchez, and J. A. Camargo. 1994. Downstream effects of a new hydropower impoundment on macrophyte, macro invertebrate and fish communities. Regulated Rivers 9:253-261. Johns, A. D. 1988. Economic development and wildlife conservation in Brazilian Amazonia. Ambio 17:302-306. Johnston, T. A., R. A. Bodaly, and J. A. Mathias . 1991. Predicting fish mercury levels from physical characteristics of boreal reservoirs. Canadian Journal of Fisheries and Aquatic Sciences 48:1468-1475. Junk, W. J. 1984. Ecology, fisheries and fish culture in Amazonia, pp. 443-476. In: H. Sioli [ed.], The Amazon: Limnology and Landscape 197 Ecology of a Mighty Tropical River and its Basin (Monographiae Biologicae v. 56). Dr. W. Junk Publishers. The Netherlands. Junk, W. J., G. M. Soares, and F. M. Carvalho. 1983. Distribution of fish in a lake of the Amazon river floodplain near Manaus (Lago Camaleao) , with special reference to extreme oxygen conditions. Amazoniana 7:397-431. Junk, W. J. and J. A. S. Nunes de Mello. 1987. Impactos ecologicos das represas hidreletricas na bacia Amazonica brasileira, pp. 367-385. In: G. Kohlhepp and A. Schrader [eds.], Homem e Natureza na Amazonia. Tiibinger Geopraphische Studien 95. Tubinger . Germany. Junk, W. J., P. B. Bayley, and R. E. Sparks. 1989. The flood pulse concept in river-f loodplain systems, pp. 110-127. In: D. P. Dodge [ed.], Proceedings of the International Large River Symposium. Canadian Special Publication in Fisheries and Aquatic Sciences 106 . King, R. D. and P. A. Tyler. 1982. Downstream effects of the Gordon River power development, South-west Tasmania. Aust. J. Mar. Freshwater Res. 33:431-442. Kinsolving, A. D. and M. B. Bain. 1993. Fish assemblage recovery along a riverine disturbance gradient. Ecological Applications 3:531-544. Klammer, G. 1984. The relief of the extra-Andean Amazon Basin, pp. 47- 83. In: H. Sioli [ed.], The Amazon: Limnology and Landscape Ecology of a Mighty Tropical River and its Basin (Monographiae Biologicae v. 56). Dr. W. Junk Publishers. The Netherlands. Krammer, D. L. and M. McClure. 1982. Aquatic surface respiration, a widespread adaptation to hypoxia in tropical freshwater fishes . Environmental Biology of Fishes 7:47-55. Kroger, R. L. 1973. Biological effects of fluctuating water levels in the Snake River, Grand Teton National Park, Wyoming. The American Midland Naturalist 89:478-481. Lacerda, L. D., W. C. Pfeiffer, A. T. Ott, and E. G. da Silveira. 1989. Mercury contamination in the Madeira River, Amazon - Hg inputs to the environment. Biotropica 21:91-93. Lacerda, L. D. and W. Salomons. 1991. Mercury in the Amazon: A Chemical Time Bomb? Dutch Ministry of Housing, Physical Planning and Environment . Lamas, I. R. and A. L. Godinho. 1996. Reproduction of the piranha Serrasalmus spilopleura, a neotropical fish with an unusual pattern of sexual maturity. Environmental Biology of Fishes 45:161-168. Lange, T. R. , H. E. Royals, and L. L. Connors. 1994. Mercury accumulation in largemouth bass (Micropterus salmoides) in a Florida Lake. Arch. Environ. Contam. Toxicol. 27:466-471. Larsson, P. 1984. Transport of PCBs from aquatic to terrestrial environments by emerging chironomids. Environmental Pollution (Series A) 34 :283-289 . 198 Lauzarme, L . , G. Loubens, and B. de Guennec . 1990. Pesca y biologia pesquera en el Mamore medio (region de Trinidad, Bolivia) Interciencia 15:452-460. Lehmkuhl, D. M. 1972. Change in thermal regime as a cause of reduction of benthic fauna downstream of a reservoir. J. Fish Res Bd Canada 29 : 1329-1332 . Leino, T. and M. Lodenius . 1995. Human hair mercury levels in Tucurui area, State of Para, Brazil. The Science of the Total Environment 175 : 199-125 . Leite, R. A. N. and M. M. Bittencourt. 1991. Impacto das hidroeletricas sobre a ictiofauna da Amazonia: 0 exemplo de Tucurui, pp. 85-100. In: A. L. Val, R. Figliuolo and E. Feldberg [eds.], Bases Cientificas para Estrategias de Preservacao e Desenvolvimento da AmazSnia: Fatos e Perspectivas , Volume 1. INPA. Manaus . Amazonas Brazil . Lockhart, W. L . , J. F. Uthe, A. R. Kenney, and P. M. Mehrle. 1972. Methylmercury in northern pike (Esox lucius) : Distribution, elimination, and some biochemical characteristics of contaminated fish. J. Fish. Res. Board Can. 29:1519-1523. Lowe-McConnell, R. H. 1975. Fish Communities in Tropical Freshwaters . Longman. New York. Lowe-McConnell, R. H. 1987. Ecological Studies in Tropical Fish Communities. Cambridge University Press. Cambridge, u. K. Lowe-McConnell, R. H. 1991a. Ecology of cichlids in South American and African waters, excluding the African Great Lakes, pp. 60-85. In: M. H. A. Keenleyside [ed.], Cichlid Fishes: Behaviour, Ecology and Evolution. Chapman & Hall. New York, New York. U. S. A. Lowe-McConnell, R. H. 1991b. Natural history of fishes in Araguaia and Xingu Amazonian tributaries, Serra do Roncador, Mato Grosso, Brazil. Ichthyol. Explor. Freshwaters 2:63-82. Ludwig, J. A. and J. F. Reynolds. 1988. Statistical Ecology: A Primer on Methods and Computing. John Wiley & Sons, Inc. New York. New York. Magee, P. L. 1990. "The water is our land": Peasants of the river Tocantins, Brazilian Amazonia. Ph.D. Dissertation. University of Florida. Gainesville. Malm, 0. 1991. Contaminacao Ambiental e Humana por Mercurio na Regiao Garimpeira de Ouro do Rio Madeira, Amazonia. Ph. D. Dissertation. Universidade Federal do Rio de Janeiro. Rio de Janeiro. Brazil. Malm, 0., W. C. Pfeiffer, W. R. Bastos, and C. M. M. Souza. 1989. Utilizacao do acessorio de geracab de vapor frio para analise de mercurio em investigates ambientais por espectrof ometria de absorcao atomica. Ciencia e Cultura 41:88-92. Malm, O., w. c. Pfeiffer, C. M. M. Souza, and R. Reuther. 1990. Mercury pollution due to gold mining in the Madeira River basin Brazil Ambio 19:11-15. 199 Malm. 0., w. C. Pfeiffer, and C. M. M. Souza. 1991. Main pathways of mercury in the Madeira River area, Rondonia, Brazil, pp. 515-518. In: J. G. Farmer [ed.], Proceedings of the 8th International Conference Heavy Metals in the Environment. Edinburgh. U. K. Malm, 0., F. J. P. Branches, H. Akagi , M. B. Castro, W. C. Pfeiffer, M . Harada, W. R. Bastos, and H. Kato . 1995. Mercury and methylmercury in fish and human hair from the Tapajos River basin, Brazil. The Science of the Total Environment 175:141-150. Martinelli, L . A., J. R. Ferreira, B. R. Forsberg, and R. L. Victoria. 1988. Mercury contamination in the Amazon: A gold rush consequence. AMBIO 17:252-254. Mclvor, C. C. and W. E. Odum. 1988. Food, predation risk, and microhabitat selection in a marsh fish assemblage. Ecology 69:1341-1351. McKim, J. M., G. F. Olson, G. W. Holcombe, and E. P. Hunt. 1976. Long- term effects of methylmercury chloride on three generations of brook trout {Salvelinus fontinalis) ; Toxicity, accumulation, distribution, and elimination. J. Fish. Res. Board Can. 33-2726- 2739. Melack, J. M. and T. R. Fisher. 1983. Diel oxygen variations and their ecological implications in Amazonian floodplain lakes. Arch. Hydrobiol. 98:422-442. Merona, B. 1990. Amazon fisheries: General characteristics based on two case-studies. Interciencia 15:461-468. Merona, B., J. L. de Carvalho, and M. M. Bittencourt. 1987. Les effets immediats de la fermeture du barrage de Tucurui (Bresil) sur 1 ' ichtyofaune en aval. Rev. Hydrobiol. trop. 20:73-84. Meuleman, C, M. Leermakers, and W. Baeyens . 1995. Mercury speciation in Lake Baikal. Water, Air, and Soil Pollution 80:53 9-551. Moller, P. 1995. Electric Fishes: History and Behavior. Chapman & Hall. New York. New York. Monosowski, E. 1990. Lessons from the Tucurui experience. Water Power & Dam Construction February 1990:29-34. Monosowski, E. 1991. Dams and sustainable development in Brazilian Amazonia. Water Power & Dam Construction May 1991:53-54. Morrison, K. A. and N. Therien. 1995. Changes in mercury levels in lake whitefish (Coregonus clupeaformis) and northern pike (Esox lucius) in the LG-2 reservoir since flooding. Water, Air, and Soil Pollution 80:819-828. Moyle, P. B. and B. Vondracek. 1985. Persistence and structure of the fish assemblage in a small California stream. Ecology 66:1-13. Mozeto, A. A., T. A. Stone, I. F. Brown, and D. L. Skole, 1990. O uso do sistema geografico de informacao e de sensoriamento remoto na 200 avaliacao do impacto ambiental na Estacao Ecologica da UHE Samuel, Rondonia, Brasil. Interciencia 15:265-271. Novoa, D. 1986. Una revision de la situacion actual de las pesquerias multiespecif icas del Rio Orinoco y una propuesta del ordenamiento pesquero. Memoria Sociedad de Ciencias Naturales La Salle 125/126:167-191. Novoa, D. , F. Ramos, and E. Cartaya. 1984. Las pesquerias artesanales del Rio Orinoco, sector Caicara - Cabruta, parte 1. Mem. Soc . Cien. Nat. La Salle 121:163-215. Nriagu, J. 0. 1994. Mercury pollution from the past mining of gold and silver in the Americas. The Science of the Total Environment 149:167-181. Nriagu, J. O., W. C. Pfeiffer, 0. Malm, C. M. M. de Souza, and G. Mierle. 1992. Mercury pollution in Brazil. Nature 356:389. Odinetz-Collart, 0. 1987. La peche crevetiere de Macrobrachium amazonicum (Palaemonidae) dans le Bas-Tocantins , apres la fermeture du barrage de Tucurui (Bresil) . Rev. Hydrobiol trop 20:131-144. Odinetz-Collart, 0. 1991. Tucurui Dam and the populations of the prawn Macrobrachium amazonicum in the Lower Tocantins River (PA-Brazil) : A four year study. Arch. Hydrobiol. 122:213-227. Olson, K. R., H. L. Bergman, and P. O. Fromm. 1973. Uptake of methyl mercuric chloride and mercuric chloride by trout: A study of uptake pathways into the whole animal and uptake by erythrocytes in vitro. Journal of the Fisheries Research Board of Canada 30:1293-1299. Payne, A. I. and M. J. Harvey. 1989. An assessment of the Prochilodus platensis Holmberg population in the Pilcomayo River fishery, Bolivia using scale-based and computer-assisted methods. Aquaculture and Fisheries Management 20:233-248. Petts, G. E. 1984. Impounded Rivers. John Wiley & Sons. New York. Petts, G. E. 1990. Regulation of large rivers: Problems and possibilities for environmentally-sound river development in South America. Interciencia 15:388-3 95. Petts, G. E., J. G. Imhof, B. A. Manny, J. F. B. Maher, and S. B. Weisberg. 1989. Management of fish populations in large rivers: A review of tools and approaches, pp. 578-588. In: D. P. Dodge [ed.], Proceedings of the International Large River Symposium Can. Spec. Publ . Fish. Aquat . Sci . 106. Pfeiffer, W. C. and L. D. Lacerda. 1988. Mercury inputs in the Amazon region, Brazil. Environmental Technology Letters 9:325-330. Pfeiffer, W. C, L. D. de Lacerda, O. Malm, C. M. M. Souza, E. G Silveira, and W. R. Bastos. 1989. Mercury concentrations in inland waters of gold-mining areas in Rond6nia, Brazil. The Science of the Total Environment 87/88:233-240. 201 Pfeiffer, W. C, 0. Malm, C. M. M. de Souza, L. D. de Lacerda, E. G. Silveira, and W. R. Bastos. 1991. Mercury in the Madeira River ecosystem, Rondonia, Brazil. Forest Ecology and Management 38:239- 245. Porvari, P. 1995. Mercury levels of fish in Tucurui hydroelectric reservoir and in River Moju in Amazonia, in the state of Para, Brazil. The Science of the Total Environment 175:109-117. Potter, L . , D. Kidd, and D. Standiford. 1975. Mercury levels in Lake Powell. Environmental Science and Technology 9:41-46. Power, M. 1984a. Depth distributions of armored catfish: Predator- induced resource avoidance? Ecology 65:523-528. Power, M. 1984b. Habitat quality and the distribution of algae-grazing catfish in a Panamanian stream. Journal of Animal Ecoloov 53-357- 374. Quiros, R. 1990. The Parana River basin development and changes in the lower basin fisheries. Interciencia 15:442-451. Quiros, R. and S. Cuch. 1989. The fisheries and limnology of the lower Plata basin, pp. 429-443. In: D. P. Dodge [ed.], Proceedings of the International Large River Symposium. Can. Spec. Publ . Fish. Aquat. Sci. 106. Raymond, H. L. 1988. Effects of hydroelectric development and fisheries enhancement on spring and summer chinook salmon and steelhead in the Columbia River basin. North American Journal of Fisheries Management 8:1-24. Reuther, R. 1994. Mercury accumulation in sediment and fish from rivers affected by alluvial gold mining in the Brazilian Madeira River basin, Amazon. Environmental Monitoring and Assessment 32:239-258. Ribeiro, M. C. L. B. and M. Petrere Jr. 1990. Fisheries ecology and management of the jaraqui (Semaprochilodus taeniurus, S. insignis) in Central Amazonia. Regulated Rivers 5:195-215. Ribeiro, M. C. L. B., M . Petrere Jr., and A. F. Juras . 1995. Ecological integrity and fisheries ecology of the Araguaia-Tocantins river basin, Brazil. Regulated Rivers 11:325-350. Rieman, B. E., R. c. Beamesderfer , S. Vigg, and T. P. Poe. 1991. Estimated loss of juvenile salmonids to predation by northern squawfish, walleyes, and smallmouth bass in John Day Reservoir, Columbia River. Transactions of the North American Fisheries Society 120:448-458. Riggs, A. 1979. Studies of the hemoglobins of Amazonian fishes: An overview. Comp. Biochem. Physiol. 62A: 257-271. Roberts, T. R. 1974. Osteology and classification of the Neotropical characoid fishes of the families Hemiodontidae (including Anodontinae) and Parodontidae . Bulletin of the Museum of Comparative Zoology 146:411-472. 202 Rosemberg, D. M. , R. A. Bodaly, and P. J. Usher. 1995. Environmental and social impacts of large scale hydroelectric development: Who is listening? Global Environmental Change 5:127-148. Saint-Paul, U. and G. M. Soares . 1987. Diurnal distribution and behavioral responses of fishes to extreme hypoxia in an Amazon floodplain lake. Env. Biol. Fish. 20:91-104. Salati, E. 1985. The Climatology and Hydrology of Amazonia, pp. 18-28. In: G. T. Prance and T. E. Love joy [eds.], Amazonia. Pergamon Press Ltd. Great Britain. U. K. Saltveit, s. J., j. E. Brittain, and A. Lillehammer. 1987. Stoneflies and river regulation - a review, pp. 117-129. In: J. F. Craig and J. B. Kemper [eds.], Regulated Streams: Advances in Ecology. Plenum Press. New York. Santos, G. M. 1986/1987. Composicao do pescado e situacao da pesca no estado de Rondonia. Acta Amazonica 16/17 (no. unico) , Suplemento: 43-84 . Santos, G. M. 1991. Pesca e Ecologia dos Peixes de Rondonia. Ph. D. Dissertation. Instituto Nacional de Pesquisas da Amazonia and Fundacao Universidade Federal do Amazonas . Manaus, Amazonas . Brazil . Santos, G. M. , E. J. G. Ferreira, and M. Jegu. 1993. Natureza e aplicabilidade da avaliacao de impactos ambientais (AIA) na Amazonia brasileira. In: E. J. G. Ferreira, G. M. dos Santos, E. L. M. Leao, and L. A. Oliveira [eds.], Bases Cientlficas para Estrategias de Preservacao e Desenvolvimento da Amazonia, Vol. II. Instituto Nacional de Pesquisas da Amazonia. Manaus. Brazil. Santos, U. M. , M. N. G. Ribeiro, and A. C. F. N. S. Tancredi . 1986/87. Estudo preliminar sobre a hidroquimica da bacia de Jaci-Parana (RO) . Acta Amazonica 16/17 Sup .: 143-150 . Saul, W. G. 1975. An ecological study of fishes at a site in upper Amazonian Ecuador. Proceedings of the Academy of Natural Sciences of Philadelphia 127:93-134. Schlosser, I. J. 1982. Fish community structure and function along two habitat gradients in a headwater stream. Ecological Monographs 52:395-414. Schlosser, I. J. 1985. Flow regime, juvenile abundance, and the assemblage structure of stream fishes. Ecology 66:1484-1490. Schlosser, I. J. 1987. The role of predation in age- and size-related habitat use by stream fishes. Ecology 68:651-659. Schlosser, I. J. 1991. Stream fish ecology: A landscape perspective Bioscience 41:704-712. Sedell, J. R., j. £. Richey, and F. J. Swanson. 1989. The river continuum concept: A basis for expected ecosystem behavior of verv large rivers?, pp. 49-55. In: D. P. Dodge [ed. ] , Proceedings of the International Large River Symposium. Canadian Special Publication in Fisheries and Aquatic Sciences 106. 203 Serra, A. 1956. Atlas Climatologico do Brasil, Volume II (Frequencias e Fenomenos) . Conselho Nacional de Geografia e Servico Meterologico . Rio de Janeiro, RJ. Brazil. Serra, M. T. F. 1989. Planning hydroelectric projects. Hemisphere Summer 1989 . Shrimpton, R., R. Giugliano, and N. M. Rodrigues. 1979. Consumo de alimentos e alguns nutrientes em Manaus . Acta Amazonica 9:117-141. Silva, C. P. D. 1993. Alimentacao e distribuicao espacial de algumas especies de peixes do igarape do Candiru, Amazonas , Brasil. Acta Amazonica 23:271-285. Silva, C. P. D. 1995. Community structure of fish in urban and natural streams in the Central Amazon. Amazoniana 13:221-23 6. Sioli, H. 1984. The Amazon and its main affluents: Hydrography, morphology of the river courses, and river types, pp. 127-165. In: H. Sioli [ed.], The Amazon: Limnology and Landscape Ecology of a Mighty Tropical River and its Basin (Monographiae Biologicae v. 56). Dr. W. Junk Publishers. The Netherlands. Skole, D. and C. Tucker. 1993. Tropical deforestation and habitat fragmentation in the Amazon: Satellite data from 1978 to 1988. Science 260:1905-1910. Slotton, D. G., C. R. Goldman, R. P. Axler, and J. E. Reuter. 1987. Mercury accumulation in a new reservoir system, pp. 63-65. Proceedings of the International Conference on Heavy Metals in the Environment. New Orleans, Louisiana. Smith, N. J. H. 1981. Man, Fishes and the Amazon. Columbia University Press . New York. Soares, M. G. M. 1979. Aspectos ecologicos (alimentacao e reproducao) dos peixes do igarape do Porto, Aripuana, MT. Acta Amazonica 9 :325-352 . Sorensen, J. A., G. E. Glass, K. W. Schmidt, J. K. Huber, and G. R. Rapp, Jr. 1990. Airborne mercury deposition and watershed characteristics in relation to mercury concentrations in water, sediments, plankton, and fish of eighty northern Minnesota lakes Environ. Sci. Technol. 24:1716-1727. Sreenivasan, A. 1964. A hydrological study of a tropical impoundment, Bhavanisagar Reservoir, Madras State, India, for the years 1955- 61. Hydrobiologia 24:514-53 9. Sternberg, R. 1985. Hydroelectric energy: An agent of change in Amazonia (northern Brazil), pp. 471-494. In: J. F. Calzonetti and B. D. Solomon [eds.], Geographical Dimensions of Energy. D. Reidel Publishing Company. Dordrecht. Germany. Stewart-Oaten, A., W. R. Murdoch, and K. R. Parker. 1986. Environmental impact assessment: "Pseudoreplication" in time? Ecology 67:929- 204 Stone, T. A., I. F. Brown, and G. M. Woodwell. 1991. Estimation, by remote sensing, of deforestation in central Rondonia, Brazil. Forest Ecology and Management 38:291-304. Taphorn, D. C. 1992. The Characiform Fishes of the Apure River Drainage, Venezuela. UNELLEZ - Guanare, Portuguesa. Venezuela. ter Braak, C. F. J. 1995. Ordination, pp. 91-173. In: R. H. G. Jongman, C. F. J. ter Braak, and O. F. R. Van Tongeren [eds.], Data Analysis in Community and Landscape Ecology. Cambridge University Press . Trotzki, H. W. and R. W. Gregory. 1974. The effects of water flow manipulation below a hydroelectric power dam on the bottom fauna of the upper Kennebec River, Maine. Transactions of the American Fisheries Society 103:318-324. Tundisi, T. M. , J. G. Tundisi, A. Saggio, A. L. Oliveira Neto, and E. G. Spindola. 1991. Limnology of the Samuel Reservoir (Brazil, Rondonia) in the filling phase. Verh. Internat. Verein. Limnol 24 : 1482-1488 . Turner, R. M. and M. M. Karpiscak. 1980. Recent vegetation changes along the Colorado River between Glen Canyon dam and Lake Mead, Arizona. Geological Survey Professional Paper 1132. Underwood, A. J. 1994. On beyond BACI: Sampling designs that might reliably detect environmental disturbances. Ecological Applications 4:3-15. Val, A. L. and V. M. F. de Almeida-Val . 1995. Fishes of the Amazon and their Environment: Physiological and Biochemical Aspects. Springer-Verlag. Berlin. Germany. Vanicek, C. D. , R. H. Kramer, and D. R. Franklin. 1970. Distribution of Green River fishes in Utah and Colorado following closure of the Flamming Gorge dam. The Southwestern Naturalist 14:297-315. Vannote, R. L., G. w. Minshall, K. W. Cummins, J. R. Sedell, and C. E. Cushing. 1980. The River Continuum Concept. Canadian Journal of Fisheries and Aquatic Sciences 37:130-137. Vari, R. P. 1982. Systematics of the Neotropical characoid genus Curimatopsis (Pisces: Characoidei) . Smithsonian Contributions to Zoology 373 . Vari, R. P. 1989a. Systematics of the Neotropical characiform genus Curimata Bos c (Pisces: Charac i formes ) . Smithsonian Contributions to Zoology 474 . Vari, R. p. 1989b. Systematics of the Neotropical characiform genus Psectrogaster Eigenmann and Eigenmann (Pisces: Characif ormes ) . Smithsonian Contributions to Zoology 481. Vari, R. p. 1991. Systematics of the Neotropical characiform genus Stemdachnerina Fowler (Pisces: Ostariophysi) . Smithsonian Contributions to Zoology 507. 205 Vari, R. p. 1992a. Systematics of the Neotropical characiform genus Cyphocharax Fowler (Pisces: Ostariophysi) . Smithsonian Contributions to Zoology 529. Vari, R. p. 1992b. Systematics of the Neotropical characiform genus Curimatella Eigenmann and Eigenmann (Pisces: Ostariophysi), with summary comments on the Curimatidae. Smithsonian Contributions to Zoology 533 . Veiga, M. M. , J. A. Meech, and N. Onate. 1994. Mercury pollution from deforestation. Nature 368:816-817. Voelz, N. J. and J. V. Ward. 1991. Biotic responses along the recovery gradient of a regulated stream. Canadian Journal of Fisheries and Aquatic Sciences 48:2477-2490. Walburg, c. H. 1971. Loss of young fish in reservoir discharge and year- class survival, Lewis and Clark Lake, Missouri River, pp. 441-448 In: Gordon E. Hall [ed.], Reservoir Fisheries and Limnology American Fisheries Society Special Publication no. 8. Washington, Walburg, C. H., G . L. Kaiser, and P. L. Hudson. 1971. Lewis and Clark Lake tailwater biota and some relations of the tailwater and reservoir fish populations, pp. 449-467. In: Gordon E. Hall [ed ] Reservoir Fisheries and Limnology. American Fisheries Society Special Publication no. 8. Washington, D.C. Walker, K. F., T. J. Hillman, and W. D. Williams. 1978. Effects of impoundments on rivers: An Australian case study. Verh Internat Verein. Limnol. 20:1695-1701. Walsh, S. J. 1990. A systematic revision of the neotropical catfish family Ageneiosidae (Teleostei: Ostariophysi: Silurif ormes ) Ph D. Disstertation. University of Florida. Gainesville. Ward, J V. and J. A. Stanford. 1979. The Ecology of Regulated Streams. Plenum Press. New York. Ward, J V. and J. A. Stanford. 1983. The serial discontinuity concept of lotic ecosystems, pp. 29-42. In: T. D. Fontaine, III and S M Bartell [eds.], Dynamics of Lotic Ecosystems. Ann Arbor Science Ann Arbor. Michigan. Ward, J. y. and J. A. Stanford. 1987. The ecology of regulated streams- Past accomplishments and directions for future research pp 391- 409. In: J. F. Craig and J. B. Kemper [eds.], Regulated' Streams • Advances m Ecology. Plenum Press. New York. Ward, J. V. and J. A. Stanford. 1995, Ecological connectivity in alluvial river ecosystems and its disruption by flow regulation Regulated Rivers 11:105-119. Welcomme, R L. 1979. Fisheries Ecology of Floodplain Rivers. Longman Inc . New York . WelC°Tu^ber 2621985' ^ Fisheries ' F-A'°- Fisheries Technical Paper BIOGRAPHICAL SKETCH Joao Paulo Viana was born in Rio de Janeiro, but was raised in Brasilia. While a child, he enjoyed watching documentaries about nature on TV but did not pay much attention to the nature around him. His parents had a small property on the outskirts of Brasilia (at that time a "frontier") with nice streams and gallery forests. However, as a complex adolescent, he would rather spend his weekends in the city instead of in the woods. When he started university he was determined to get a degree on physics or electrical engineering. In his first semester he found out that he was better fitted for biology. He volunteered his spare time at the university working in phytosociological studies, and later with systematics of green algae. But all plants are green. Then, small, slimy, and smelly creatures, some of them with over 100 lateral line scales, caught his attention, and Joao Paulo settled definitively with the fish. As many Brazilians do, he never paid much attention to the Amazon- until his first visit. Now, he can't get the Amazon out of his mind. He hopes he can spend as many years as possible of what remains of his life working there. 206 I certify that I have read this study and that in my opinion it conforms to acceptable standards of scholarly presentation and is fully adequate, in scope and quality, as a dissertation for the degree of Doctor of Philosophy. Claire L. Schelske, Chair Carl S. Swisher Eminent Scholar in Water Resources I certify that I have read this study and that in my opinion it conforms to acceptable standards of scholarly presentation and is fully adequate, in scope and quality, as a dissertation for the degree of Doctor of Philosophy. c Carole C. Mclvor, Cochair Assistant Professor of Fisheries and Aquatic Sciences I certify that I have read this study and that in my opinion it conforms to acceptable standards of scholarly presentation and is fully adequate, in scope and quality, as a dissertation for the degree of Doctor of Philosophy. J Kent k . Redf ord Associate Professor of Forest Resources and Conservation I certify that I have read this study and that in my opinion it conforms to acceptable standards of scholarly presentation and is fully adequate, in scope and quality, as a dissertation for the degree of Doctor of Philosophy. Carter R. Gilbert Professor of Zoofogy I certify that I have read this study and that in my opinion it conforms to acceptable standards of scholarly presentation and is fully adequate, in scope and quality, as a dissertation for the degree of Doctor of Philosophy. ^ -J\ Frank A. Chapman Assistant Professor of Fisheries and Aquatic Sciences I certify that I have read this study and that in my opinion it conforms to acceptable standards of scholarly presentation and is fully adequate, m scope and quality, as a dissertation for the degree of Doctor of Philosophy. Nigel J. H. Smith Professor of Geography This dissertation was submitted to the Graduate Faculty of the College of Agriculture and to the Graduate School and was accepted as partial fulfillment of the requirements for the degree of Doctor of Philosophy. August, 1997 /^.