Document(s) 7 de 11

Yoshimi Sato
Estação de Hidrobiologia e Piscicultura de Três Marias
Companhia de Desenvolvimento dos Vales do São Francisco e do Paranaíba (CODEVASF)
Três Marias, MG, Brazil

Hugo P. Godinho
Graduate Program on Vertebrate Zoology
Pontifical Catholic University of Minas Gerais
Belo Horizonte, MG, Brazil

CHARACTERISTICS OF THE BASIN

Geography

The São Francisco River was first encountered by Europeans on the 4th of October, 1501 – Saint Francis’ Day – by Américo Vespúcio and Gaspar Lemos, hence the river’s current name.⁵¹² Its basin covers an area of 631,133 km², or 7.4% of Brazil’s territory. The headwaters lie in the Canastra Hills, in the southern part of the state of Minas Gerais. After running north for about 2,300 km, through the states of Minas Gerais and Bahia, it turns east to run another 400 km between the states of Bahia, Pernambuco, Sergipe, and Alagoas to empty into the Atlantic Ocean.

The basin lies between 21^o 00' and 7^o 00' degrees of latitude (Figure 1) and at altitudes of up to 1,600 m above sea level. This area encompasses diverse climate conditions: annual average air temperatures of 18 to 27^oC, relatively high evaporation rates of 2,300 to 3,000 mm/year, 2,400 to 3,300 hours of light/year, ecological domains ranging from Atlantic forest to Cerrado and Caatinga, and climates varying from the humid tropical to semi-arid.⁵¹³

Geology

The variety of soil types in the São Francisco Basin is due mainly to the diversity of geological formation and topography. Latosoils and podozolyc soils predominate from the headwaters down to Petrolina, where the river turns towards the Atlantic. These soils are usually covered with cerrado and caatinga vegetation, the latter in the semi-arid regions. Detailed description of the São Francisco Basin soils is given in PLANVASF (1989).

⁵¹² Théry, 1980

⁵¹³ CODEVASF, 1991

River Profile

The São Francisco Basin is usually divided into 4 segments: the upper (from the source to the town of Pirapora, MG), central (from Pirapora to Remanso, BA), sub-central (from Remanso to Paulo Afonso, BA) and lower (from Paulo Afonso to the Atlantic Ocean) river sections. The main geographic characteristics of each segment are shown in Table 1. The river has 36 tributaries, of which only 19 are perennial. The main perennial tributaries to the west of the river are the Abaeté, Paracatu, Urucuia, Carinhanha, Corrente and Grande, while on the eastern side, the main perennial tributaries are the Pará, Paraopeba, das Velhas and Verde Grande (Figure 1).⁵¹⁴

FIGURE 1. Map of the São Francisco River Basin showing principal features mentioned in text

⁵¹⁴ CETEC, 1983

TABLE 1. Main characteristics of the geographic regions of the São Francisco River Basin⁵¹⁵

During the summer, the upper-central and lower segments of the river are prone to flooding caused by rains either on the headwaters or on the lower part of the river, respectively. Annual average river discharge is in the order of 100 x 10⁹ m³ or 3,150 m³/s.

Brazil has over 3 x 10⁶ ha of reservoirs of which more than 23% are located in the São Francisco Valley. The large Três Marias, Sobradinho, Itaparica, Moxotó, Paulo Afonso complex and Xingó are large dams that have been built across the mainstem of the São Francisco River (Figure 1). Six further smaller dams have been built on tributaries of the Upper and Central São Francisco. Only two of these smaller dams have had demonstrable effects on migratory fish (Cajuru on the Pará River and

⁵¹⁵ MG = state of Minas Gerais, BA = state of Bahia; ¹ PLANVASF, 1989; ² Paiva, 1982; ³ Silva, 1981; ⁴ CODEVASF, 1991

Gafanhoto on the Paraopeba River); the remaining dams are beyond the natural distribution of these fish.

Water Characteristics

Upper São Francisco River and tributaries

Limnological parameters of the São Francisco main river channel in the stretch between the towns of Três Marias and Pirapora, in the state of Minas Gerais, are shown in Table 2.

TABLE 2. Limnological parameters of different habitats in the São Francisco River⁵¹⁶

In the das Velhas River, an important São Francisco tributary, water temperature and turbidity are similar to those of the São Francisco. However, during the dry season the pH may reach 12 and conductivity 300 µS/cm, due to the limestone nature of the region. In the other tributaries, the Paraopeba and Pará, these values did not substantially differ from those of the São Francisco.⁵¹⁷

^{516 1} CETEC, 1983; ² Sabará, 1996;³ Esteves et al., 1985; ⁴ Pinheiro, 1981;⁵ UFRPE, 1999

⁵¹⁷ CETEC, 1983

Marginal lagoons

Physico-chemical parameters of several marginal lagoons of the Upper São Francisco were obtained by Sato and co-workers (1987) and, over a three year period, by Sabará (1996) for three marginal lagoons in the Central São Francisco. The three lagoons of the central river section, the Curral de Vara, Cajueiro and Juazeiro, were connected to the main river channel during the 1993/1994 floods. Two years later two of these still had large water volumes, but the Juazeiro dried up completely after just over one year. Conductivity in the Curral de Vara was higher than in the other marginal lagoons, probably because it is located in a carbonate-rich karstic landscape (Table 2).

Três Marias Reservoir

Três Marias Reservoir is warm, oligotrophic, and monomictic: it is vertically stratified in November-February when the temperature difference between the epiliminium and hypoliminium is always greater than 3^oC, and destratifies in July with vertical mixing during the dry season. Data on some parameters of this reservoir are shown in Table 2., together with characteristics of the Sobradinho, Itaparica and Paulo Afonso reservoirs.

Habitats Used by Migratory Species

Role of floodplains in migration

In tropical rivers, the floodplains – areas seasonally inundated by the lateral overflow of rivers and lakes⁵¹⁸ – are used by a large part of the fish community as habitat for feeding, reproduction and refuge.⁵¹⁹ During the dry season the flooded plains become isolated from the main channel. Some of these areas are perennially filled with water while the remaining dry out until the next flood. Colonisation by fish occurs during flooding and, as the waters recede at the start of the dry season, fish tend to return to the river. For those fish that remain after the connection with the river is cut off, high levels of predation, gradual exhaustion of food supply, and, in some cases, reduced oxygen levels and progressively less water⁵²⁰

⁵¹⁸ Junk et al., 1989; Junk & Welcomme, 1990

⁵¹⁹ Welcomme, 1979

⁵²⁰ Junk et al. 1989

lead to gradual elimination of species in a sequence that may vary from lagoon to lagoon.

The São Francisco River is rich in floodplains and marginal lagoons, particularly in the stretch between the town of Pirapora, MG, and the Sobradinho Reservoir. Welcomme (1990) estimated that below Três Marias Dam the floodplains occupy an area of about 2,000 km². The widest overflows are registered in the Central São Francisco (2–18 times the river width, averaging 9 km, and reaching 16 km at Januária, MG and 84 km at Xique-Xique, BA).

The importance of the São Francisco floodplains as migratory fish nursery habitat has long been recognised. Travelling in the area in 1817, Saint-Hillarie was probably the first to document the marginal lagoons,⁵²¹ created when the river overflows its banks between September and January, most intensely in December.

After adults reproduce in the mainstem and tributaries, eggs and larvae of the migratory fishes are carried downstream and, borne by floods, reach the marginal lagoons, which provide good habitat for the young with abundant live food (phytoplankton, zooplankton and other microorganisms) and relatively high temperatures.⁵²² Under such conditions growth is rapid, and in a few weeks the juveniles are ready to re-enter the river. Since Moojen, many have recognised the floodplains, especially their lagoons, as special fish nurseries.⁵²³

In order to examine the role of lagoons in the recruitment of fishes into the reservoir, Sato et al. (1987) estimated fish richness in 81 marginal lagoons along a 130 km segment of the Upper São Francisco above Três Marias Reservoir. Twenty-eight of the lagoons were permanent, whereas the remaining ones dried up during the dry season. They varied from 3 to 70 ha in size and from 1.5 to 4 m in depth. Thirty-seven fish species were identified, representing 50% of the species present in Três Marias area.⁵²⁴ Among the thirty-seven species, ten were migratory, and of these, juveniles of Salminus brasiliensis (<600 g), Leporinus elongatus (<40 g), Prochilodus affinis (<80 g), Prochilodus marggravii (<70 g) and Pseudoplatystoma corruscans (<600 g), captured in the lagoons, were not

⁵²¹ Sato et al., 1987

⁵²² Moojen, 1940

⁵²³ for review see Menezes, 1956; Godinho, 1986; Sato et al., 1987

⁵²⁴ Britski et al., 1984

present in the Três Marias Reservoir. At the time of the study, 25% of the biomass caught in experimental fisheries in the reservoir were of the adults of migratory species, indicating that their recruitment originated from marginal lagoons above the reservoir rather than from reproduction in the reservoir.

Pompeu (1997) carried out a recent two-year study on the effect of floodplain dryness on the fish communities of three marginal lagoons in the Central São Francisco. All three lagoons were connected to the main channel in the rainy season of 1993/1994 and thereafter remained isolated for the remaining period of study. The water level in two (Curral de Vara and Cajueiro) did not change substantially during the study, whereas the other (Juazeiro) dried out. Forty-eight species were captured, 44 in Curral de Vara and 34 in each of Cajueiro and Juazeiro. Seven of these were migratory: Brycon lundii, Leporinus reinhardti, Leporinus taeniatus, P. affinis, P. marggravii, P. corruscans and S. brasiliensis. Progressive reduction in species richness was registered in all lagoons throughout the study, caused probably by natural mortality and illegal fishing. In Cajueiro, migratory species disappeared significantly faster than non-migratory ones. Although the same tendency was observed in the other two lagoons, the differences were not significant.

Upper São Francisco River

Três Marias Reservoir – The Três Marias Reservoir, filled in 1960, was the first large hydroelectric reservoir built in Brazil. It was originally constructed for flood control in the Central São Francisco, but now also generates electricity. The reservoir extends 100 km south in the state of Minas Gerais, covering an area of 105,000 ha.

The fish community lives only in the littoral zone of the reservoir, as there are no naturally occurring pelagic species in the São Francisco River. During the lowest water levels, the surface area of the reservoir is reduced by 20%, exposing extensive areas of dry land that is colonized by terrestrial vegetation – primarily grass. As the reservoir is devoid of rooted aquatic macrophytes, this vegetation functions as a temporary refuge and food for fish as the water levels rise. Due to the oligotrophic conditions of the reservoir, the flooded grass may constitute the main source of food for some species. Periphyton growing on submerged trees also constitutes a significant food source.

The reservoir also receives a number of tributaries of various sizes other than the main river. The largest of these is the Paraopeba River, which provides fluvial habitat for the fish of the reservoir.

The Três Marias Dam is 75 m high and has no mechanism for fish passage, effectively splitting the Upper São Francisco River into two parts.

Above Três Marias Reservoir – The first part of the Upper São Francisco River extends 150 km above the Três Marias Reservoir to the river source in the springs of the Canastra. Although located at higher elevations, in many places this part of the river is lined with marginal lagoons that are subject to periodic flooding. In the past, 28 of these lagoons were permanent.⁵²⁵ However, 20% have now been drained for agriculture, with a corresponding reduction in fish production.

Below Três Marias Dam – The first part of the river below the Três Marias Dam extends about 140 km downstream to the town of Pirapora. The riparian vegetation here is probably the best preserved of the entire river. Many islands and rapids are present, and the stretch receives the first significant tributary, the Abaeté River, a rocky-bottomed highland river with many falls, about 32 km below the dam. Both the main river and the tributary are practically devoid of floodplains.

During most of the rainy season (the period of migratory fish reproduction), the water temperature from Três Marias Dam to the Abaeté River is usually 3–6^oC below that of the Abaeté. This is because the reservoir is thermally stratified at this time⁵²⁶ and water for the turbines is taken from the bottom of the reservoir. Many migratory species appear to spawn in the Abaeté River, but spawning apparently does not occur in the main São Francisco channel between Três Marias Dam and the Abaeté River.

Central São Francisco River

The Central São Francisco River is a long stretch of about 1,200 km in which the river runs slowly and freely without significant falls or other obstacles, enabling navigation between Pirapora, MG and the Sobradinho Reservoir in Bahia. It is also characterised by many floodplains. The most important tributaries are on the west bank: the Paracatu, Urucuia, Carinhanha,

⁵²⁵ Sato et al., 1987

⁵²⁶ Esteves et al., 1985

Corrente and Grande rivers. On the east bank, there are two further main tributaries: the das Velhas and the Verde Grande rivers. Of these, the Paracatu River is particularly notable for its important fisheries and extensive floodplains. In addition, the relatively small Pandeiros River, a tributary from the east that joins the São Francisco close to Januaria, MG, contains a swamp that is a particularly important nursery habitat for migratory fishes.

The Sobradinho Reservoir, the largest hydroelectric reservoir in Brazil (approx. 420,000 ha in surface area and up to 34 x 10⁹ m³ in volume), takes up the northern (downstream) end of the central section of the São Francisco River. Constructed to regulate river flow and feed downriver hydroelectric plants, the waters are shallow and the dam has no mechanism for fish passage (although the navigation lock may serve this purpose). The rising waters of the reservoir obliterated extensive floodplains when the reservoir was filled in the early 1970s.

Relative to the Três Marias Reservoir, the Sobradinho is considerably shallower. During low water, the surface area of the reservoir is reduced by as much as 70%, which reduces fish habitat and fish production. Three sections of the reservoir are recognised, based on differing characteristics.⁵²⁷ Section 1, adjacent to the dam, includes 60% of the reservoir area. This region has an average depth of 15 m and is devoid of aquatic vegetation. Strong SE–NW winds make fishing difficult in this section. The next adjacent upriver section, Section 2, includes 30% of the reservoir area, with an average depth of 8 m. This section is extensively covered by aquatic macrophytes, providing ample fish refuge and food. In 1987, 75% of the reservoir fishery production came from this section.⁵²⁸ Section 3 contains the junction between the river and the upper reservoir. This area contains numerous marginal lagoons, and in 1987 was considered the principal nursery area for migratory species of the region.

The Semiarid Project has proposed diversion of water for irrigation to northeastern Brasil from the Sobradinho Reservoir, as well as from the downstream Itaparica and Xingó reservoirs and the river at Cordobó. This proposal was first put forward in the 19th century and has been very controversial for over 80 years, but currently appears to be experiencing a revival. Studies on potential impacts on fish fauna are presently under way, but have not yet been made public.

⁵²⁷ CEPED/PROTAM, 1987

⁵²⁸ CEPED/PROTAM, 1987

Sub-central and Lower São Francisco River

This portion of the São Francisco extends from the Sobradinho Reservoir to the ocean, dropping 450 m in approximately 950 km. The first stretch, from the Sobradinho Dam to the Itaparica Dam 450 km downstream, has no floodplains, only small and seasonal tributaries, and is greatly influenced by the operation of the Sobradinho hydroelectric power plant. Downstream of the Sobradinho Reservoir, in the region of Petrolina, one of the largest irrigation projects of the São Francisco supports extensive fruit growing. From the Itaparica Dam to the Xingó Reservoir, the river has a complex series of hydroelectric dams, and migratory species have practically disappeared from this stretch. The final dam on the river, the Xingó, was finished in 1994. This reservoir is located within the São Francisco canyon, and does not cover a much greater surface area than the original river bed. Below the Xingó Dam, the São Francisco River runs for a short distance in the canyon before reaching flatter land near the Atlantic Ocean. This area historically included a large number of marginal lagoons, but many of these have now been converted into agricultural land. Exotic fish species, especially Nile tilapia, have been introduced into all of the reservoirs.

MIGRATORY SPECIES AND MIGRATION PATTERNS

This section summarises the present status of migratory fish species in the various regions of the São Francisco Basin.

The fish fauna of the São Francisco River is composed of about 152 species.⁵²⁹ About 8% of the species migrate to reproduce. Among these, seven species are probably long-distance migrants and the most important commercial fishes. They are the Characiformes B. lundii, S. brasiliensis, L. elongatus, P. affinis and P. marggravii and the Siluriformes Conorhynchus conirostris and P. corruscans. Of these, B. lundii, S. brasiliensis, C. conirostris and P. corruscans are listed as “presumably threatened” species of the state of Minas Gerais.⁵³⁰

⁵²⁹ Travassos, 1960; Britski et al., 1984; Sato & Godinho, 1999

⁵³⁰ Lins et al., 1997

Reproductive migration of fish appears to be a universal phenomenon in most South American rivers.⁵³¹ The fish, which migrate annually in the São Francisco, travel up the main river channel or in tributaries towards their spawning grounds. Their migration is a cyclic phenomenon that is most pronounced from October to January during the rainy season, when the water levels tend to rise,⁵³² temperatures are higher and the days are longer.

Despite its undoubted importance, the migration of South American fresh-water fishes has not attracted the attention of scientists as much as it has that of the communities living along the rivers. Along the São Francisco, all residents are familiar with the migratory phenomenon, known locally as piracema (an indigenous word meaning pira = fish, cema = jump), but about which no more than a few scientific papers have been published. As a result, important aspects of the São Francisco River piracema, such as feeding and reproductive habitats, shoal composition and structure, and homing and distances travelled between habitats remain poorly understood.

Migratory fishes of the São Francisco are group-synchronous spawners, i.e., they spawn only once in a reproductive period, and are iteroparous, i.e., they are able to spawn again for at least several more years. Records of actual natural breeding are not available in the literature and consequently spawning sites have not been registered for most of these fishes. Nonetheless, it is believed that they spawn in the river channel. The actual breeding phenomenon, known locally as carujo, has only been described by fishermen. In the case of surubim (P. corruscans), the female is described to stand upside-down at the water surface for short periods of time, liberating eggs that are fertilized by several males that swim over her abdomen in erratic patterns. This behaviour appears to be repeated several times a day by each female.

A study that demonstrated the great migratory capacity of jucá (P. marggravii),⁵³³ tagged 1,012 fish on the São Francisco River at the future site of the Sobradinho Dam. About 10% of the marked fishes were recaptured. After 85 days one tagged P. marggravii was recaptured

⁵³¹ for review see Petrere Jr., 1985

⁵³² Aguire, 1936

⁵³³ reported by Pinheiro, 1981

800 km upriver,⁵³⁴ and after 186 days, another was found 1,100 km upriver.⁵³⁵

The most important migratory species for commercial fishing in the São Francisco are listed below. Other species, commercially important in other neotropical basins but not in the São Francisco, were not considered in this chapter. Amongst these is the mandi-amarelo (Pimelodus maculatus), which is considered migratory in some basins, but apparently only carries out short distance movements in the São Francisco during the reproductive period. We feel the fish does not present the characteristic strategies of long distance migrators in the São Francisco and thus we have not discussed it at length in this chapter.

Brycon lundii

Known in Portuguese as matrinchã, this species is an omnivorous fish endemic to the São Francisco River Basin, reaching up to seven kg in weight with females larger than males.⁵³⁶ Natural stocks of B. lundii are significantly reduced in some areas of the São Francisco River Basin, but the species remains important to both sport and commercial fishers near Três Marias Dam in Minas Gerais State.

Salminus brasiliensis

Known as dourado in Portuguese for its bright yellow colour, this species is also endemic to the São Francisco River Basin. The second largest species of the São Francisco, it is essentially a piscivore. The species can reach 1.4 m in length and 30 kg in body weight,⁵³⁷ with females growing much larger than the males.

Leporinus elongatus

This species, known in Portuguese as the piau-verdadeiro, is the only large migratory fish amongst the three genera of Anostomidae found in the São Francisco, and is the largest known member of this family of fish. It is native to two of the largest South American rivers, the trans-national

⁵³⁴ above the town of Januária, MG

⁵³⁵ above the town of Pirapora, MG

⁵³⁶ Sato et al., 1997

⁵³⁷ Ihering, 1968

Paraná-Paraguay and the São Francisco.⁵³⁸ The species is distinguished by transverse stripes on the body and three dark spots that are faint or absent in larger specimens. The fish is omnivorous, limited in its diet by its relatively small mouth. It can reach up to 7.5 kg in body weight,⁵³⁹ with females growing larger than the males.

Prochilodus affinis and Prochilodus marggravii

P. affinis and P. marggravii, known in Portuguese as curimatá-pioa and curimatá-pacu, respectively, are endemic to the São Francisco River. The latter is the largest member of the Prochilodontidae family, reaching more than 15 kg in body weight. P. affinis may grow above 6 kg, but apparently is not as important to the São Francisco fisheries as P. marggravii. All fish of this family are bottom (mud) feeders of great importance to river and reservoir fisheries in all of Brazil. In the 1980s, the Prochilodontidae, primarily Prochilodus spp., represented almost 20% of all Brazilian freshwater fishery biomass.⁵⁴⁰

Both species of Prochilodus in the São Francisco River are probably long-distance migrants, and both are commercially significant. The lower segment of the Upper São Francisco River, below the confluence with the Abaeté River, is a particularly important fishing and spawning area. Production of this species in the Três Marias and Sobradinho reservoirs was extremely high for an initial period after flooding, but has since declined dramatically.

Conorhynchus conirostris

C. conirostris, known in Portuguese as the pirá, is a unique catfish species endemic to the São Francisco,⁵⁴¹ distinctive for its lack of dorsal flattening typical of catfish, an unusual proboscis-like mouth, and a blue soft outer skin. The species feeds mainly on molluscs, but also eats insect larvae and pupae, worms and micro-crustaceans.⁵⁴² The fish is still significant to fisheries below the Três Marias Dam, but appears practically extinct above it.⁵⁴³

⁵³⁸ Fowler, 1950

⁵³⁹ Godoy, 1975

⁵⁴⁰ IBGE, 1988

⁵⁴¹ Fowler 1951, Travassos, 1960

⁵⁴² Ihering, 1933, 1936, 1938, Ihering & Azevedo, 1934, Azevedo & Vieira, 1938

⁵⁴³ Sato et al., 1987

Pseudoplatystoma corruscans

This large piscivorous catfish is known locally as surubim, and is the largest and most valuable commercial fish in the São Francisco. The fish reaches 3.3 m in length⁵⁴⁴ and over 100 kg in body weight, with females growing larger than the males.⁵⁴⁵ The species appears to be a long-distance migrant, with the section of the river below the confluence with the Abaeté River particularly important to its reproduction and fishery. Yields of surubim from the Sobradinho Reservoir were high for several years after flooding, but have declined considerably since, though still relied on by commercial fishermen. Elsewhere on the river, surubim is also scarce: it constitutes just under 0.4% of total catch below Xingó Dam, and it is listed as a presumably threatened species of the state of Minas Gerais.

IMPACTS ON MIGRATORY SPECIES

Fisheries Impacts

The São Francisco Basin is one of the most important locations for inland Brazilian fisheries. In the 1980s the basin supported about 25,000 professional fishermen.⁵⁴⁶ Fisheries have evidently declined in recent decades, along with the number of fishermen. In the 1970s, landings in the São Francisco were around 25 kg/fisherman/day, while in the 1980s they were reduced to about 11 kg/fisherman/day in the central segment.⁵⁴⁷ Since no long-term catch statistics are available, it is impossible to make good comparisons, but there is reason to believe the harvest continues to decline.

The professional fisherman of the Upper-central São Francisco

Fisheries in the São Francisco River are carried out for subsistence, for income, and for recreation. The second of these categories is termed a “professional” fisherperson, defined legally and licensed as someone whose principal source of income is from fishing. However, the techniques

⁵⁴⁴ Ihering 1946

⁵⁴⁵ Zarur, 1947 in Menezes, 1956

⁵⁴⁶ PLANVASF, 1989

⁵⁴⁷ Sato & Osório, 1988; Godinho et al., 1997

employed by these professional fisherpersons are largely artisanal, and N. Nordi (pers. com.) has recently (1997) described the professional artisanal fishermen of the Upper-central São Francisco thus:

“Four São Francisco “fishing colonies” have been organised in the state of Minas Gerais. A recent survey indicates that only approximately 600 fishermen fish regularly at present. However, this number should be considered with caution since non-registered professionals or even amateurs illegally fishing as professionals make it difficult to determine the true number.

The fisherman works with artisanal equipment made by his family. He paddles a small wooden canoe; motorized canoes are seldom seen. Species-specific equipment such as cast nets and hook and line predominate and are directed towards the most valuable species. Multi-species gear (gillnets) are also used, although the catches take non-commercial species as well. The cast nets are typically 3 m high, 30 m in circumference and 8–17 cm in mesh size. The gillnets are typically 30 m long, 3.5 m high and 12–20 cm in mesh size.

The fisherman’s daily working journey is dictated by nature, especially by fish behaviour. It is discontinuous but takes most of the day, preventing other activities from being carried out simultaneously. This apparent absence of non-stop effort and purposeful motion induces outsiders to feel, erroneously, that fishing is an indolent and disorganised activity.

A large portion of the catch is sold fresh to intermediaries. Only a few fishermen have refrigerators or freezers. The catch is usually not salted since there is no market for salty fish. Value is generally not added.

The family is made up of the fisherman, his wife and their children. The man is the head of the family. The wife, who is economically active, does her work in the husband’s company and in support of him. The lack of working opportunities outside of fishing maintains strong ties amongst family members. The families live aggregated in urban areas, usually in the poorest borough and in the poorest home of the street. The radio is the main entertainment and informative medium. Bicycles are the principal vehicle for travelling by land. The families do not consider the possibility of giving up fishing but do hope for this possibility for their children. A fixed job for their sons is a strong family aspiration and towards this end much of the family’s effort is put into their children’s formal education.”

Upper São Francisco

Partition of the Upper São Francisco by the Três Marias Dam resulted in a drastic modification of the fish fauna, especially of migratory species. In the 10–15 years that followed dam closure, Três Marias Reservoir fisheries were still based on the same migratory species found in the lower parts of the river.⁵⁴⁸ By the 1980s, however, the capture pattern had changed. Sedentary species such as the piau-branco (Schizodon knerii) and corvina (Pachyurus squamipinnis and Pachyurus francisci) replaced migratory species, with the exception of curimatã (Prochilodus spp.). In 1986, one hundred and fifty-eight active professional fishermen captured a total of about 400 metric tons/year in the Três Marias Reservoir.⁵⁴⁹

Although the fishing season in the reservoir is usually longer than that of the river, its productivity is lower and relies on small sedentary species of low value, except for Prochilodus. The reservoir fishermen’s income is thus lower than that of the river fishermen (Table 3).

Três Marias Reservoir fisheries presently rely on tucunaré (Cichla spp.; peacock bass in English), pescada-do-piaui (P. squamipinnis), mandi-amarelo (P. maculatus) and curimatã (Prochilodus spp.). Tucunaré is a sedentary piscivorous Amazonian cichlid introduced into the São

TABLE 3. Fisheries yields from Três Marias Reservoir and from the area of the São Francisco River below the reservoir in 1986⁵⁵⁰

⁵⁴⁸ SUVALE, 1973

⁵⁴⁹ Sato & Osório, 1988

⁵⁵⁰ s = sedentary, m = migratory; Adapted from Sato & Osório, 1988 in H.P. Godinho, 1998

Francisco River Basin at the end of the 1970s probably for fish cultur and sport fishing. It was first caught in experimental fisheries in the Três Marias Reservoir in 1984⁵⁵¹ and, in less than 10 years, reached the important position it holds for fisheries today. As a consequence of the tucunaré introduction, however, the populations of some small-sized fish species, such as Acestrorhynchus lacustris, Curimatella lepidura and Triporteus guentheri, have experienced heavy declines⁵⁵². Other long-distance migratory species appear in the professional catch of the reservoir, but always at low frequencies. This may mean that the floodplain area above the reservoir still functions as nursery grounds for these species, but at a much reduced scale.⁵⁵³

The lower segment of the Upper São Francisco River, below the Abaeté River, is an important fishing and spawning area for long-distance migratory species.⁵⁵⁴ Since there are no floodplains in this area, eggs and larvae are carried down to the Central São Francisco where they can find suitable habitat for development. Fisheries are based on the migrants P. marggravii, P. corruscans and S. brasiliensis, which together make up about 95% of the catches. In 1980, 130 full-time professional fishermen captured 234 metric tons/year in this area.⁵⁵⁵

Central São Francisco

The Central São Francisco remains the section of the river where migratory species are most abundant. Records of the Pirapora Professional Fishermen Colony indicate that catches in the Pirapora area in the 1980s were mainly of the migrants P. corruscans, C. conirostris, S. brasiliensis and Prochilodus spp.,⁵⁵⁶ representing 96% of the total catch. However, only a small portion of the catch was brought to the Colony for marketing, which suggests that the data presented in Table 4 are underestimates with regard to the fish production of the entire area.

To study fishing practices and productivity a fishing boat of the Pirapora Professional Fishermen Colony was accompanied for 1 week/ month over a period of 6 months in 1987.⁵⁵⁷ The boat had a crew of 8–10 fishermen and the capacity to hold 2 tons of refrigerated fish. Fishing

⁵⁵¹ Sato & Godinho, 1988

⁵⁵² H. Godinho, unpublished observations

⁵⁵³ Sato et. al., 1987

⁵⁵⁴ CODEVASF, 1988

⁵⁵⁵ CODEVASF, 1988

⁵⁵⁶ Godinho et al., 1997

⁵⁵⁷ Godinho et al., 1997

5 days/week, the boat travelled about 180 km. Fishing efforts were aimed at P. corruscans, the most valuable table fish in the São Francisco, by employing a specialized bottom drift net – the tarrafão. A large cast net held vertically in the river by two fishermen from a drifting canoe, the mouth of the net facing downstream and its lower rim touching the river bed. When a fish is encountered, it is ensnared by releasing the top edge of the net. A characterization of the catch in this study is shown in Table 5.

Lower in the Central São Francisco, in the transitional area between the river and Sobradinho Reservoir, P. corruscans was the principal species caught in the marginal lagoons.⁵⁵⁸ The tucunaré has now also been found in marginal lagoons of the Central São Francisco⁵⁵⁹ and of the Paracatu

TABLE 4. São Francisco fish captures registered at Pirapora professional fishermen colony from July to December, 1987⁵⁶⁰

TABLE 5. Fisheries yields of an artisanal fishing boat operating in the Central São Francisco (1week/month) during the period of July to December, 1987⁵⁶¹

⁵⁵⁸ for review of old literature see Menezes, 1956

⁵⁵⁹ Pompeu, 1997

⁵⁶⁰ Godinho et al., 1997

⁵⁶¹ Godinho et al., 1997

River. As this introduced species is a particularly aggressive piscivore, there is great concern that its presence will negatively impact recruitment of migratory species that rely on the lagoons as a nursery.⁵⁶²

Sub-central and Lower São Francisco

Fisheries of the Sobradinho Reservoir – The fishery productivity of the Sobradinho Reservoir was relatively high (50 kg/ha/year) for six years after the dam was completed in the early 1970s, but declined drastically during the following three years to approximately half of this value.⁵⁶³ The early high productivity was thus probably due to the increased primary productivity and decomposition of organic detritus typical of newly formed reservoirs. The large catchment area of Sobradinho Reservoir could also have contributed to the high yields, particularly of the large migratory fishes, P. marggravii and P. corruscans, which made up over 70% of the total catches.

Although no current catch statistics are available, informal information from fishermen indicates that present fisheries for migratory species in the Sobradinho have sunk to a very low level. Today the non-migratory pescada-do-piaui (Plagioscion squamosissimus) introduced from the Paranaiba River by government agencies, is the main fish caught in the reservoir.

Fisheries between Sobradinho and Xingó – Fisheries are almost absent in this portion of the São Francisco River, with the exception of a small fishery for introduced tilapia in the Itaparica Reservoir.

Fisheries below Xingó Hydroelectric Dam – Fishing in this part of the Lower São Francisco is a traditional activity involving many part-time and full-time professional fishermen. As in other parts of the river, complaints of decreased catches are often heard, especially following closure of the Xingó Dam in 1994. However, the scarcity of data on fish catches in the Lower São Francisco permits no accurate analyses of long-term trends. Early reports by Schubart (1944) and reports by various northeastern Brazilian organisations in the 1990s⁵⁶⁴ comprise the sole literature available on the subject.

⁵⁶² Godinho et al., 1994

⁵⁶³ CEPED/PROTAM, 1987

⁵⁶⁴ Costa & Coelho, 1998

In 1997, the total catch was estimated to be about 333 metric tons/ year, of which the fishing colonies at Propriá, Penedo and Piaçabuçu were responsible for more than 85%.⁵⁶⁵ Prochilodus sp. (locally known as xira, curimatã and bambá) and the marine Anchoviella (pilombeta) were the main species caught, representing, respectively, 35.1% and 32.6% of the total production.⁵⁶⁶ According to the same report, other native freshwater migratory fish comprising less than 4% of the catches in professional fisheries were Leporinus spp. (piau), juvenile Prochilodus spp. (bambá), and P. corruscans (surubim) (Table 6). The introduced species Colossoma macropomum (tambaqui – an amazonian migratory fish), Oreochromis niloticus (tilápia), Cichla spp. (tucunaré) and P. squamosissimus (pescada-do-piaui) made up 8.5% of the total catch (Table 6).

Fisheries of the freshwater prawn Macrobrachium carcinus – Very important to the Lower São Francisco fisheries is the large freshwater prawn Macrobrachium carcinus (locally known as pitu). Together with surubim, pitu is the most valuable species and the principal item in the fisherman’s income. Although there are also complaints about the reduction in its capture, there have been no significant variations in production over the last few years (at Propriá, monthly production varied from 142.7 kg in 1994 to 200.7 kg in 1997).⁵⁶⁷ However, as with the fish catches, the available data allows no prediction of production trends.⁵⁶⁸

Sport fisheries in the São Francisco – Although the São Francisco River and some of its tributaries are traditionally one of the main spots for Brazilian anglers, Godinho (2000) is the only known report on this activity. This study sampled two sites, one close to the Três Marias Dam and the other at the town of Ibiai, near the mouth of the das Velhas River. During the period of March, 1999 to April, 2000 dourado was the principal species caught at both sites, followed by mandi-amarelo, surubim and curimatã at Três Marias and by mandi-amarelo, surubim, and piau (Leporinus spp.) at Ibiai. Each angler caught 1.9 kg of fish/day at Três Marias and 1.0 kg of fish/day at Ibiai.

⁵⁶⁵ Costa & Coelho, 1998

⁵⁶⁶ Costa & Coelho 1998

⁵⁶⁷ Coelho, 1998

⁵⁶⁸ Coelho, 1998

TABLE 6. Fisheries yields in the Lower São Francisco (below Xingó Dam) in 1997, showing contribution of migratory species⁵⁶⁹

Other Impacts

The main threats to the fish fauna in the state of Minas Gerais, through which the São Francisco flows, were recently pointed out in a workshop at Belo Horizonte, MG that included representatives of most of the stakeholders involved in the fishery and its management.⁵⁷⁰ These threats were ascribed to human activities that modify habitat quality, such as hydroelectric dam construction and operation, pollution and deforestation. Introductions of species not native to the watershed are also becoming a serious threat, particularly with the rapid growth of fee fishing aquaculture – currently the main source of such introductions.⁵⁷¹

Upper São Francisco River

In the part of the Upper São Francisco River that extends 150 km above Três Marias Reservoir, 28 of the marginal lagoons subject to periodic

^{569 1} migratory species, ² marine species, ³ introduced species; Adapted from Costa & Coelho, 1998

⁵⁷⁰ A. L. Godinho, 1998

⁵⁷¹ Alves et al., 1999

flooding used to be permanent. Twenty percent of these have now been drained for agriculture. Riparian deforestation has occurred throughout this section, and large industrial complexes (mainly sugar and acetylene plants) that pollute the catchment have been built.

The Paraopeba River, one of the two significant tributaries emptying into the river above Três Marias Dam, drains part of a highly populated area with very active industry and iron mining, and also supports large sand-extraction operations. Consequently the watershed is now in an advanced stage of deterioration, and fishing in this river has been closed for several years due to pollution.

The Pará River, the other important tributary of the São Francisco River above the Três Marias Dam, was once a valuable fishing ground. Today this dam and other small hydroelectric dams, together with agriculture, sand extraction and urban and industrial pollution have considerably reduced the catches. Below the Três Marias Dam, the Abaeté, an important rocky-bottomed highland tributary with many falls, has been affected by disturbance from diamond mining.

Central São Francisco

The Central São Francisco region has suffered intense deforestation over recent decades, resulting in continuous sediment deposition in some important tributaries and in the main channel. Large irrigation projects in the area also draw on São Francisco waters.

The Urucuia, Carinhanha, Corrente and Grande rivers are less impacted by these activities, although they also run through areas of extensive agricultural development (especially the Corrente and Grande). However, intense agricultural activity has almost completely deforested the catchment of the Paracatu River, leading to heavy sediment deposition, and indiscriminate use of lead in gold mining has polluted this river further. The das Velhas River, which drains a largely industrialised and populated urban area, also carries a heavy pollutant load into the São Francisco, and the Verde Grande River occasionally dries out due to excessive water diversion for irrigation.

Lower São Francisco: Xingó Dam to the river mouth

Due to river regulation, most of the original floodplains from the Xingó Dam to the river mouth are now occupied by agriculture and irrigation

projects. Fishing communities have blamed declining catches on the absence of the original flooding pattern. As as consequence, the introduction of artificial flooding regimes in this section is now being considered by CHESF (Centrais Eletricas do São Francisco).

MANAGEMENT AND MITIGATION

Fisheries Regulation and Management

Fisheries management in the São Francisco, as in many other river basins, is based on fishing regulation and re-stocking. Despite having been in operation for decades, these management tools are frequently applied without adequate scientific basis. Management mistakes have thus been made in the São Francisco, as in other Brazilian river basins.

Brazilian fisheries regulations and fisheries development have historically been the exclusive responsibility of the Brazilian Institute for Environment and Renewable Natural Resources (IBAMA). In 2000, however, fisheries and fish culture were placed under the jurisdiction of the Ministry of Agriculture. Practical consequences of this change have not yet been observed. A few states such as Minas Gerais have now also established their own regulations, which apply only to state rivers, i.e., those that run solely within state borders. In the case of the state of Minas Gerais, this legislation is very similar to the federal legislation, with some differences on, for example, a more restrictive fishing season in state rivers. The main regulatory measures used for fisheries management to date are these:

Seasonal limitations

Fishing is limited during the reproductive period of the main migratory commercial species. This season usually extends from mid-November to mid-February, but exact dates are set every year by IBAMA with, at times, additional restrictions from the state agency.

Size and catch limits

Minimum size limits for the main commercial migrants are shown in Table 7. These size limits apply to both commercially and sport-caught fish, but limits on the amount of fish that can be kept (catch limits) vary with the time of year and the class of fishermen. For professional

fishermen, there are no catch limits except during the reproductive period, while sport fishermen are limited to 30 kg of fish plus one fish of any weight. During the reproductive period, both professional and sport fishermen are limited to 5 kg plus one fish of any weight.

TABLE 7. Minimum size allowed for capturing the main commercial migratory fish of the São Francisco Basin⁵⁷²

Closed areas

Fishing is prohibited at distances of less than 1 km below and above dams, waterfalls and rapids, for both safety reasons and, as the fish aggregate in these places, to avoid potentially excessive impacts on the fish stocks. Fishing is also permanently prohibited in two large São Francisco tributaries, the das Velhas and the Paraopeba, due to alleged pollution.

Fishing gear

The main gear used in professional fisheries of the São Francisco are gillnets and cast nets, with restrictions on mesh size, and, for gillnets, on length and height. Sport fishermen are allowed to only use hook and line, and during the reproductive season, both professional and sport fishermen are limited to the use of only hook and line.

Two further gear types, while illegal, are also used extensively in the São Francisco by professional fishermen. These are the tarrafão and the harpoon. The tarrafão, described earlier, is generally used near the shore in stretches of river previously cleaned of bottom debris, such as submerged tree trunks. This gear is highly selective for bottom-dwellers like P. corruscans (Table 5). Harpoons are used particularly for valuable species like P. corruscans and S. brasiliensis.

⁵⁷² IBAMA, 1995

Effectiveness of enforcement

Enforcement is a state responsibility borne by federal IBAMA and state environmental agencies. The Forestry Police, a segment of the state military police, are the principal enforcement agents. Often, as in the case of the state of Minas Gerais, the number of enforcement officers is ineffective and most of them lack specific training. Adequate equipment is also not always available. Fishing out of season is probably the most common violation of the law, mainly committed by the professional fishermen. Illegal fishing gear (primarily gillnets that are too long) is also very common among these fishermen. Sport fishermen usually commit violations such as keeping fish of sub-legal size and fishing in prohibited areas.

Fish Passages

Fish ladders have been built in some Brazilian river basins, mainly in the Paraná River. Evaluation of their efficiency, however, has generally not been done.⁵⁷³ Only two fish ladders have been constructed in the São Francisco Basin. The oldest is a small fish ladder located in the headwaters of the Pandeiros River; it appears not to be currently in operation and no reports on its efficiency are available. Judging by its location and design, the ladder can be presumed to have only minor, if any, favourable impact on the migratory fish fauna of the region.

A small fish ladder was also recently built in a dam on the Paraopeba River close to a thermal electric plant near the town of Igarapé. An evaluation of the ladder’s effect on the Paraopeba migratory fish stocks was begun before its completion in 1994 and is still underway. The capture of marked P. affinis and L. elongatus above it have demonstrated its efficiency for these species,⁵⁷⁴ and experimental fisheries before and after construction have shown increased yields of migratory fishes above the ladder. However, the increased yields may have resulted exclusively from displacement of fish from below the dam; marginal lagoons and suitable reproductive area are absent in the section of river made accessible by the ladder.

⁵⁷³ Godinho et al., 1991

⁵⁷⁴ Alves & Vono, 1997; Alves, personal communication

Re-stocking Programs

The São Francisco River has been re-stocked with hatchery-reared fish since the early 1980s by the federal agency for the development of the São Francisco Valley (Companhia de Desenvolvimento dos Vales do São Francisco e do Paranaíba, CODEVASF), which has 6 hatcheries in operation along the São Francisco River and the Hydroelectric Company of the São Francisco (CHESF) has one. The mandate of these hatcheries is to produce fingerlings both for fish farms in the São Francisco Valley and for re-stocking the river and reservoirs. Fingerlings of introduced species are also produced by some of these hatcheries for the same purposes.

The Três Marias Hatchery station, located at the Três Marias hydroelectric power plant in the Upper São Francisco, was built as a legal requirement to mitigate the effects of the dam on fish. It is the principal CODEVASF hatchery that is devoted to production of fingerlings exclusively of species native to the São Francisco watershed. Technology for large-scale propagation of the principal commercial species of the river (primarily migratory species) has been developed here, and since 1983 about 7 million fingerlings (~10–20 cm in length) of P. marggravii, P. affinis, L. elongatus, B. lundii, S. brasiliensis and P. corruscans have been produced. These have been stocked primarily in the Upper São Francisco above the Três Marias Dam. The technology for mass production of C. conirostris is also being developed and this species will also be re-stocked in the near future.

Although the São Francisco re-stocking program is almost 20 years old, there are no quantitative reports on its efficiency, though qualitative reports indicate they are having an effect. For example, artisanal, sport and experimental catches indicate that B. lundii stocks, which were practically extinct locally, have been tenuously re-established above Três Marias Dam after re-introduction began in 1988. Others species, such as L. elongatus, P. marggravii and P. affinis, that were rare in early catches above the Três Marias Dam, have also been increasing in number following re-stocking that began in the 1980s.

Some re-stocking has also taken place in urban areas. Pampulha Lake, a 3 km² urban reservoir in Belo Horizonte that was originally constructed

for water supply, is in the catchment of the Upper São Francisco. In 1990 it was re-stocked with fingerlings of Prochilodus sp., L. elongatus, B. lundii and S. brasiliensis. Experimental and sport fisheries 23 months after re-stocking (Table 8) caught representatives of all species, apparently after good growth.⁵⁷⁵

TABLE 8. Growth of fish re-stocked at Pampulha Lake, Belo Horizonte, in the 1990s⁵⁷⁶

Water management

Water management is an important tool to increase fisheries production.⁵⁷⁷ One approach, used effectively for rivers in some areas of the world, is the provision of artificial floods to enhance natural spawning of migratory species, as has been achieved in some other regions of the world.⁵⁷⁸ This approach has not yet been tried in Brazil, though it is likely that such an approach would revitalize marginal lagoons and augment nursery habitats in both central and lower portions of the river and stimulate spawning in the lower river section, where river fluctuations are currently absent. Studies on these applications have started: CODEVASF has requested a proposal from the US Bureau of Reclamation for implementing artificial flooding below the Xingó Dam, and projects studying the needs for flooding marginal lagoons in other portions of the river have been recently proposed.

⁵⁷⁵ Godinho et al., 1992

⁵⁷⁶ Godinho et al., 1992

⁵⁷⁷ Welcomme, 1989; Alves, 1995

⁵⁷⁸ Welcomme, 1989

RECOMMENDATIONS FOR CONSERVATION AND RESEARCH

Conservation Status of São Francisco Migratory Fish Species

In a recent workshop in Bolivia, attempts were made to identify priorities for conservation actions in large geographic areas of high freshwater biodiversity in Latin America and the Caribbean.⁵⁷⁹ It was pointed out that over 85% of the freshwater biodiversity in the region is seriously threatened, more so than terrestrial biodiversity. The study indicated that the complex São Francisco ecoregion is regionally outstanding and ranked its conservation status as “endangered”. The basin was assigned a high priority for conservation at the regional scale.

At a workshop held to establish conservation priorities in the state of Minas Gerais, the fish fauna was included in such discussions for the first time.⁵⁸⁰ The São Francisco River main channel and associated floodplains, from Três Marias Dam to the border with the state of Bahia, were indicated as having special biological importance. The Peruaçu River and Pandeiros River wetlands also fell into this category. The large tributaries in the region – Carinhanha, Paracatu, Urucuia, Verde Grande and das Velhas – were placed in the category of extreme biological importance because they include spawning habitats, have high species richness, and are essential to the integrity of the São Francisco floodplain areas.

Proposed Conservation Actions

An overview of the conservation status of the various segments of the São Francisco River is shown in Figure 2. Actions proposed to prevent further damage of the São Francisco River should be directed toward controlling pollution, providing sustainable fisheries, and promoting recovery of the original riparian vegetation. Since the ecological balance within the basin is already precarious, any plans to divert its waters will drastically affect it.⁵⁸¹

⁵⁷⁹ Olson et al., 1998

⁵⁸⁰ Costa et al., 1998

⁵⁸¹ Olson et al., 1998

FIGURE 2. Map of the São Francisco River Basin showing conservation status of river sections

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