Document(s) 5 de 11

Emiko Kawakami de Resende
Empresa Brasileira de Pesquisa Agropecuária (Embrapa)
Embrapa Pantanal
Corumbá, MS, Brazil

CHARACTERISTICS OF THE BASIN

Introduction

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

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

²⁷² Also see Chapter 2

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

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

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

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

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

²⁷³ Lundberg et al., 1998

²⁷⁴ Lima Barros Dolabella, 2000

²⁷⁵ Agostinho et al., 1995; Bonetto, 1998

²⁷⁶ Bonetto, 1998

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

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

Upper Paraguay

Geography, geology and river profile

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

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

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

²⁷⁷ Bonetto, 1998

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

The Pantanal

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

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

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

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

²⁷⁹ Ab’Saber, 1988

²⁸⁰ Lima Barros Dolabella, 2000

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

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

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

Social characteristics

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

²⁸¹ Resende, 1998

²⁸² Resende, 1998

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

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

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

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

²⁸³ PCBAP, 1997

²⁸⁴ PCBAP, 1997

²⁸⁵ Lima Barros Dolabella, 2000

²⁸⁶ PCBAP, 1997

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

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

Lower Paraguay

Geography, geology and river profile

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

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

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

²⁸⁷ PCBAP, 1997

²⁸⁸ Bonetto, 1998

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

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

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

Social characteristics

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

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

²⁸⁹ PCBAP, 1997

²⁹⁰ Encyclopaedia Britanica, 1980

²⁹¹ CIH, 1997

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

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

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

High Paraná

Geography, geology and river profile

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

²⁹² Carron, 2000

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

²⁹⁴ Mochek & Pavlov, 1996; Civic, 1999

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

²⁹⁶ Mochek & Pavlov, 1996

²⁹⁷ Mochek & Pavlov, 1996

²⁹⁸ Civic, 1999

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

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

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

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

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

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

³⁰⁰ García, 1999

³⁰¹ García, 1999

³⁰² García, 1999

Social characteristics

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

Middle and Lower Paraná

Geography, geology and river profile

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

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

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

³⁰³ Inter-America Development Bank, 1997

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

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

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

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

Río de la Plata

Geography, geology and river profile

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

³⁰⁴ Bonetto, 1998

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

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

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

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

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

Habitats Used by Migratory Species

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

³⁰⁵ 1991 census

³⁰⁶ www.ramsar.org/profiles_argentina.htm

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

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

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

MIGRATORY SPECIES AND MIGRATION PATTERNS

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

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

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

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

³⁰⁹ Nión, 1996

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

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

FIGURE 2. Migratory fish life cycle in the Pantanal

³¹⁰ Resende et al. 1996a

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

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

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

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

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

³¹² Sverlij & Espinach-Ros, 1986

³¹³ Bayley, 1973

³¹⁴ Resende, unpublished

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

Characids

Brycon spp.

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

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

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

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

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

Leporinus spp.

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

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

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

³¹⁷ Silva, 1990

³¹⁸ Resende, unpublished

³¹⁹ Mesquita, 1992

³²⁰ Resende, personal observation

³²¹ Resende et al., 1998

³²² Mesquita, 1992

Piaractus mesopotamicus

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

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

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

³²³ Quirós, 1993

³²⁴ Silva, 1985

³²⁵ Resende, unpublished

³²⁶ Conceição, 1988; Silva, 1985

³²⁷ Lima et al., 1984a, 1984b

³²⁸ Resende, unpublished

Prochilodus spp.

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

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

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

³²⁹ Cabrera and Candia, 1964; Cordiviola, 1971

³³⁰ CIH, 1997

³³¹ Bayley, 1973

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

Salminus maxillosus

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

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

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

³³² Cabera & Candia, 1964

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

³³⁴ Sverlij & Espinach-Ros, 1986

³³⁵ Resende et al., 1996b

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

Schizodon borellii

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

Silurids (catfish)

Hemisorubim platyrhynchos

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

Paulicea luetkeni

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

³³⁶ Sverlij & Espinach-Ros, 1986

³³⁷ Sverlij & Espinach-Ros, 1986

³³⁸ Espinach-Ros & Delfino, 1993

³³⁹ Resende et al., 1998

³⁴⁰ Mesquita, 1992

³⁴¹ Resende et al., 1996b

³⁴² Resende, unpublished

³⁴³ Quirós, 1993

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

Pimelodus spp.

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

Pinirampus pirinampu

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

Pseudoplatystoma spp.

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

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

³⁴⁴ Quirós, 1993

Pterodoras granulosus

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

Sorubim lima

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

IMPACTS ON MIGRATORY SPECIES

Fisheries

Fishing in the Pantanal

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

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

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

³⁴⁵ Resende et al., 1996b

³⁴⁶ Resende, unpublished

³⁴⁷ Bayley, 1973

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

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

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

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

³⁴⁸ Lima & Chabalin, 1984

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

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

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