Document(s) 4 de 11

Angelo Antonio Agostinho
Luiz Carlos Gomes
Harumi Irene Suzuki
Horácio Ferreira Júlio Jr.
Núcleo de Pesquisas em Limnologia, Ictiologia e Aqüicultura (Nupelia)
Universidade Estadual de Maringá
Maringá, Paraná, Brazil

CHARACTERISTICS OF THE BASIN

Geography and Geology

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

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

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

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

River Profile

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

Water Uses

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

⁶ IBGE, 1990

⁷ Petri & Fulfaro, 1983

⁸ Agostinho et al., 2000

⁹ CERH-SP, 1990

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

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

Habitats Used by Migratory Species

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

Spawning habitats

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

¹⁰ Agostinho et al., 1995a

¹¹ Agostinho et al., 1995a

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

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

Nursery habitats

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

¹³ Modified from Vazzoler et al., 1997a

¹⁴ Agostinho et al., 2000

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

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

Feeding habitats

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

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

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

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

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

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

¹⁶ Thomaz, 1991

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

¹⁸ Agostinho et al., 1994a

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

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

MIGRATORY SPECIES AND MIGRATION PATTERNS

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

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

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

¹⁹ Agostinho & Júlio Jr., 1999

²⁰ Suzuki, 1992

²¹ Bonetto, 1963

²² Bonetto & Castello, 1985

* Short distance migrants migrate less than 100 m

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

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

Distribution

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

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

²⁴ Gomes & Agostinho, 1997

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

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

Feeding

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

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

²⁵ Agostinho et al., 1994a

²⁶ Nakatani et al., 1997

²⁷ Nakatani et al., 1997

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

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

SPECIES	FEEDING CATEGORY	MORPHOLOGICAL MODIFICATION	PRINCIPAL FOOD ITEMS
Brycon orbignyanus	Insectivorous	Anterior mouth, conical teeth	Coleoptera, hemiptera
Hemisorubim platyrhynchos	Piscivorous	Wide mouth, dental plates	Small fishes
Leporinus elongatus	Omnivorous	Pronounced incisive teeth	Plants and insects
Leporinus obtusidens	Omnivorous	Pronounced incisive teeth	Plants and insects
Paulicea luetkeni	Piscivorous	Wide mouth, dental plates	Large and small fishes
Piaractus mesopotamicus	Omnivorous	Pronounced molar teeth	Plants, fruit and insects
Pimelodus maculatus	Omnivorous	Wide mouth, dental plates	Fishes, invertebrates and plants
Pinirampus pirinampu	Piscivorous	Wide mouth, dental plates	Small fishes and juveniles of large fishes
Prochilodus lineatus	Iliophagous	Protrusible mouth, gizzard and very long intestine	Detritus and sediments
Pseudoplatystoma corruscans	Piscivorous	Wide mouth, dental plates	Small bodied fishes and juveniles of other fishes
Pterodoras granulosus	Omnivorous	Wide sub-inferior mouth, long gut	Plants and molluscs
Rhaphiodon vulpinus	Piscivorous	Very developed canine teeth	Small fishes
Rhinelepis aspera	Iliophagous	Suctorial inferior mouth, very long intestine	Detritus and sediments
Salminus hilarii	Piscivorous	Wide mouth, large teeth	Fishes
Salminus maxillosus	Piscivorous	Wide mouth, large teeth	Fishes
Steindachneridion sp.	Piscivorous	Wide mouth, dental plates	Small bodied fishes, juveniles of other fishes

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

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

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

Growth

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

³⁰ Agostinho, unpublished data

³¹ Agostinho, unpublished data

³² Goulding, 1980

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

³⁴ Lizama & Vazzoler, 1993

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

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

Abundance

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

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

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

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

³⁶ Santos, 1999

³⁷ FUEM-Nupélia-Furnas, 1999

³⁸ CESP,1996

³⁹ Dias, 1995; CESP, 1996

⁴⁰ FUEM-Nupélia-Copel, 1998

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

⁴² Gomes & Agostinho, 1997

⁴³ Agostinho, 1994

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

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

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

⁴⁴ Gomes & Agostinho, 1997; Veríssimo, 1999

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

⁴⁶ Agostinho et al., 1999c

⁴⁷ Suzuki, 1999

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

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

Migration Patterns

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

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

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

⁵⁰ Godoy, 1975

⁵¹ Agostinho et al., 1993a

⁵² Agostinho et al., 2002

⁵³ João Henrique Pinheiro Dias, personal communication

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

Spawning

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

⁵⁴ Agostinho et al., 2002

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

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

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

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

⁵⁵ Godoy, 1975

⁵⁶ Godoy, 1975

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

⁵⁸ Verissimo, 1999

⁵⁹ Gomes & Agostinho, 1997

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

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

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

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

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

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

Reproductive Strategy

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

⁶¹ Agostinho et al., 2001

⁶² Vazzoler et al., 1991

⁶³ Balon, 1984

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

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

Timing of Spawning

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

⁶⁴ Nakatani et al., 1997

⁶⁵ Fenerich-Verani et al., 1984

⁶⁶ Suzuki, 1992

⁶⁷ Gomes & Agostinho, 1997

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

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

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

Spawning Sites and Migratory Behaviour

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

⁶⁸ Agostinho et al., 1993a

⁶⁹ Gomes & Agostinho, 1997

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

⁷¹ Bonetto & Castello, 1985

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

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

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

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

⁷³ Modified from Agostinho et al., 1993a

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

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

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

Description of Principal Species

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

⁷⁴ Agostinho et al., 1993a

⁷⁵ Nakatani et al., 1997

⁷⁶ Agostinho, unpublished data

⁷⁷ Agostinho et al., 1993b

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

Brycon orbignyanus

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

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

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

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

⁷⁸ Agostinho & Julio Jr, 1999

⁷⁹ Quirós, 1990

⁸⁰ Schubart, 1943; Godoy, 1975

⁸¹ Hahn et al., 1997

⁸² Godoy, 1975; Lowe-McConnell, 1986

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

⁸⁴ Vazzoler et al., 1997a

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

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

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

Hemisorubim platyrhynchos

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

Leporinus elongatus

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

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

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

⁸⁷ Santos & Formagio, 2000

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

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

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

Leporinus obtusidens

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

⁸⁸ Godoy, 1975

⁸⁹ Hahn et al., 1997

⁹⁰ Gaspar da Luz et al., in press

⁹¹ Godoy, 1975

⁹² Fernandes, 2000

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

⁹⁴ Agostinho & Julio Jr, 1999

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

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

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

Paulicea luetkeni

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

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

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

⁹⁶ Mello et al., 1999

⁹⁷ Araya, 1999

⁹⁸ Jorge & Moreira Filho, 1996

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

¹⁰⁰ Agostinho & Júlio Jr., 1999

¹⁰¹ Santos & Ferreira,1999

¹⁰² Pelli et al., 2000

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

¹⁰⁴ Lopes et al., 1994

Piaractus mesopotamicus

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

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

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

Pimelodus maculatus

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

¹⁰⁵ Hahn et al., 1997

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

¹⁰⁷ Milstein et al., 2000

¹⁰⁸ Jordão & Volpato, 2000

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

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

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

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

¹¹³ Bonetto, 1963; Godoy, 1967

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

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

Pinirampus pirinampu

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

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

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

¹¹⁵ Gaspar da Luz et al., in press

¹¹⁶ Agostinho et al., 1999a

¹¹⁷ Godinho et al.,1977; Lamas, 1993

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

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

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

¹²¹ Sato et al., 1999, 2000

¹²² Fenerich et al., 1975

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

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

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

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

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

Prochilodus lineatus

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

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

¹²⁵ Hahn et al., 1997

¹²⁶ Agostinho et al., 1999a

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

¹²⁸ Swarça et al., 1999, in press

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

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

¹³¹ Agostinho & Zalewski, 1995; Veríssimo, 1999

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

¹³³ Hahn et al., 1997

¹³⁴ Lowe McConnell, 1975; Bowen, 1983

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

¹³⁶ Bowen, 1983

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

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

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

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

¹³⁷ Bowen et al., 1984

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

¹³⁹ Bayo & Yuan, 1996

¹⁴⁰ Agostinho et al., 1993a

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

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

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

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

¹⁴⁵ Quirós, 1988; Borghetti et al., 1994

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

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

¹⁴⁸ Coser et al., 1984

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

Pseudoplatystoma corruscans

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

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

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

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

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

¹⁵¹ Ranzani-Paiva et al., 1995, 2000

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

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

¹⁵⁴ Godinho et al., 1997

¹⁵⁵ Marques, 1993

¹⁵⁶ Agostinho & Julio Jr, 1999

¹⁵⁷ Marques, 1993

¹⁵⁸ Marques et al., 1992

¹⁵⁹ Palmeira, 1990; Mateus & Petrere, in press

¹⁶⁰ Sato et al., 1997

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

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

Pterodoras granulosus

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

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

¹⁶¹ Suzuki, 1992

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

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

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

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

¹⁶⁶ Souza et al.,1997

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

¹⁶⁸ Agostinho & Julio Jr, 1999

¹⁶⁹ Hahn et al., 1992, 1997

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

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

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

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

Rhaphiodon vulpinus

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

¹⁷⁰ Agostinho & Julio Jr, 1999

¹⁷¹ Stevaux et al., 1994

¹⁷² Pilati et al., 1999

¹⁷³ Gosso & Iwaszkiw, 1993

¹⁷⁴ Suzuki, 1992

¹⁷⁵ Agostinho et al., 1994a

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

¹⁷⁷ Satake et al., 1991

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

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

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

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

Rhinelepis aspera

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

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

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

¹⁷⁹ Fuem.Nupélia/Itaipu Binacional, 1998

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

¹⁸¹ Suzuki, 1992

¹⁸² Iglesias & Schubart, 1999

¹⁸³ Suzuki, 1992

¹⁸⁴ Moravec et al., 1993a, 1993b

¹⁸⁵ Nelson, 1949

¹⁸⁶ Agostinho et al., 1995b

¹⁸⁷ Monteiro, 1963, 1965

¹⁸⁸ Agostinho & Barbieri, 1987a, 1987b

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

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

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

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

Salminus hilarii

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

¹⁸⁹ Agostinho et al., 1995b

¹⁹⁰ Castro et al., 1999

¹⁹¹ Delariva & Agostinho, 2001

¹⁹² Agostinho et al., 1991

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

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

¹⁹⁵ Agostinho & Barbieri, 1987a, 1987b

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

¹⁹⁷ Armbruster, 1998a, 1998b

¹⁹⁸ Godoy, 1975

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

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

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

Salminus maxillosus

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

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

¹⁹⁹ Godoy, 1975

²⁰⁰ Godoy, 1975

²⁰¹ Nomura, 1973

²⁰² Kohn et al., 1997

²⁰³ Godoy, 1975

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

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

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

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

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

Steindachneridion spp.

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

²⁰⁵ Vazzoler, 1996

²⁰⁶ Godoy, 1975

²⁰⁷ Suzuki, 1992

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

²⁰⁹ Godoy, 1975

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

²¹¹ Matsushita & Souza, 1994

²¹² Margarido & Galetti Jr., 1999

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

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

IMPACTS ON MIGRATORY SPECIES

Fisheries Impacts

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

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

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

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

Artisanal fisheries

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

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

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

²¹⁶ Petrere & Agostinho, 1993

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

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

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

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

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

²¹⁹ Thornton et al., 1990

²²⁰ Agostinho et al., 1999a

²²¹ Okada et al., 1996

²²² Okada et al., 1996

²²³ Paiva et al., 1994

²²⁴ Marshal, 1984

²²⁵ Miranda et al., 2000

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

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

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

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

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

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

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

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

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

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

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

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

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

²³⁰ Marques, 1993; Petrere & Agostinho 1993

²³¹ Buck, 1988; Petrere & Agostinho, 1993

²³² Petrere & Agostinho, 1993

²³³ Gomes & Agostinho, 1997

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

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

Subsistence fisheries

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

Sport fisheries

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

²³⁴ Agostinho et al., 1994b

²³⁵ Agostinho et al., 1999b

Other Impacts

Genetic effects

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

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

²³⁶ Revaldaves et al., 1997

²³⁷ Nei, 1978

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

Negative impacts of dams

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

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

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

²³⁹ Petrere et al., 2002

²⁴⁰ Agostinho et al., 1999a

²⁴¹ Godoy, 1975

²⁴² Monteiro, 1963

²⁴³ Agostinho et al., 1995a, 1999a

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

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

Positive impact of dams

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

Agriculture and ginseng extraction

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

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

²⁴⁵ Barbosa et al., 1999

²⁴⁶ Agostinho & Zalewski, 1995

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

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

Mining and navigation

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

MANAGEMENT AND MITIGATION

Legislation

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

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

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

²⁴⁷ Alzuguir, 1994

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

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

²⁵⁰ Law Number 6938; August 31, 1981

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

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

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

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

Fish Passages

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

²⁵² Agostinho & Gomes, 1997

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

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

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

²⁵³ Agostinho et al., 2002

²⁵⁴ Pardo River, a tributary of Paraná River

²⁵⁵ Godoy, 1985; Quirós, 1988

²⁵⁶ Law No 2250/SP, 28/12/1927

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

²⁵⁸ Charlier, 1957

²⁵⁹ Godoy, 1957, 1975

²⁶⁰ Borghetti et al., 1993; 1994

²⁶¹ Godinho et al., 1991

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

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

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

²⁶² Godoy, 1985

²⁶³ Fernandez, 2000

²⁶⁴ Borghetti et al., 1994

²⁶⁵ Agostinho et al., 1993a

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

Fish Elevators

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

Stocking

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

²⁶⁶ 7,855 marked and 315 recaptured

²⁶⁷ FUEM.Nupélia-Itaipu Binacional, 1990

²⁶⁸ Convenio SECY T, 1996

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

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

RESERVOIRS	LARGE MIGRATORY	OTHERS
Água Vermelha	5,284,000	5,786,200
Bariri	1,382,700	2,578,600
Barra Bonita	741,700	9,227,500
Ibitinga	4,630,690	2,682,600
Nova Avanhandava	1,930,892	2,878,300
Promissão	22,498,300	13,206,220
Ilha Solteira	6,345,600	11,454,807
Jupiá	7,991,150	4,289,800
Jurumirim	5,584,900	8,940,700
Total	56,389,932	61,044,727

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

Protected Areas

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

²⁶⁹ CESP, 1996

²⁷⁰ Agostinho et al., 1999a

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

RECOMMENDATIONS FOR CONSERVATION AND RESEARCH

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

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

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

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

²⁷¹ Agostinho & Zalewski, 1996

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

Proposed Conservation Strategy

A conservation strategy for the area should consider:

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

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