Asunto(s)

RESUMEN

The relationships between fish composition, connectivity and morphometry of 103 lagoons in nine freshwater ecoregions (FEOW) between 2·83° S and 37·64° S were evaluated in order to detect possible congruence between the gradient of species richness and similarities of assemblage composition. Most lagoons included in the study were <2 km(2) , with a maximum of 3975 km(2) in surface area. Combined surface area of all lagoons included in the study was 5411 km(2) . Number of species varied locally from one to 76. A multiple regression revealed that latitude, attributes of morphometry and connectivity, and sampling effort explained a large amount of variability in species richness. Lagoon area was a good predictor of species richness except in low latitude ecoregions, where lagoons are typically small-sized and not affected by marine immigrants, and where non-native fish species accounted for a significant portion of species richness. Relationships between species and area in small-sized lagoons (<2 km(2) ) is highly similar to the expected number in each ecoregion, with systems located between 18·27° S and 30·15° S attaining higher levels of species richness. Similarities in species composition within the primary, secondary and peripheral or marine divisions revealed strong continental biogeographic patterns only for species less tolerant or intolerant to salinity. Further support for the FEOW scheme in the eastern border of South America is therefore provided, and now includes ecotonal systems inhabited simultaneously by freshwater and marine species of fishes.

Asunto(s)

RESUMEN

The Patos Lagoon basin is a large (201 626 km(2) ) and complex drainage system in southern Brazil. The lagoon is 250 km long and 60 km wide, covering an area of 10 360 km(2) . The exchange of water with the Atlantic Ocean occurs through a 0·8 km wide and 15 m deep inlet, fixed by 4 km long jetties, at the southernmost part of the Patos Lagoon. The estuarine area is restricted to its southern portion (10%), although the upper limit of saline waters migrates seasonally and year to year, influenced by the wind regime and river discharge. The known number of recorded limnetic fish species is 200, but this number is expected to increase. A higher endemism is observed in fish species occurring in upper tributaries. The basin suffers from the direct impact of almost 7 million inhabitants, concentrated in small to large cities, most with untreated domestic effluents. There are at least 16 non-native species recorded in natural habitats of the Patos Lagoon basin, about half of these being from other South American river basins. Concerning the fishery, although sport and commercial fisheries are widespread throughout the Patos Lagoon basin, the lagoon itself and the estuarine area are the main fishing areas. Landing statistics are not available on a regular basis or for the whole basin. The fishery in the northern Patos Lagoon captures 31 different species, nine of which are responsible for most of the commercial catches, but only three species are actually sustaining the artisanal fishery: the viola Loricariichthys anus: 455 kg per 10 000 m(2) gillnet per day, the mullet Mugil liza: 123 kg per 10 000 m(2) gillnet per day and the marine catfish Genidens barbus: 50 kg per 10 000 m(2) gillnet per day. A decline of the fish stocks can be attributed to inadequate fishery surveillance, which leads to overfishing and mortality of juveniles, or to decreasing water quality because of urban and industrial activities and power production. Global climatic changes also represent a major threat to the Patos system by changing the frequency of El Niño-La Niña-Southern Oscillation (ENSO).

Asunto(s)

RESUMEN

The aquatic habitats of the Taquari-Antas river basin (in the Patos Lagoon basin, southern Brazil) are under marked environmental transformation because of river damming for hydropower production. In order to provide an information baseline on the fish fauna of the Taquari-Antas basin, we provide a comprehensive survey of fish species based on primary and secondary data. We found 5,299 valid records of fish species in the basin, representing 119 species and 519 sampling sites. There are 13 non-native species, six of which are native to other Neotropical river basins. About 24% of the total native species are still lacking a taxonomic description at the species level. Three native long-distance migratory species were recorded (Leporinus obtusidens, Prochilodus lineatus, Salminus brasiliensis), as well as two potential mid-distance migrators (Parapimelodus nigribarbis and Pimelodus pintado). Although there is only one officially endangered species in the basin (S. brasiliensis), restricted range species (21.7% of total species) should be considered in conservation efforts.

Asunto(s)

RESUMEN

The aquatic habitats of the Taquari-Antas river basin (in the Patos Lagoon basin, southern Brazil) are under marked environmental transformation because of river damming for hydropower production. In order to provide an information baseline on the fish fauna of the Taquari-Antas basin, we provide a comprehensive survey of fish species based on primary and secondary data. We found 5,299 valid records of fish species in the basin, representing 119 species and 519 sampling sites. There are 13 non-native species, six of which are native to other Neotropical river basins. About 24% of the total native species are still lacking a taxonomic description at the species level. Three native long-distance migratory species were recorded (Leporinus obtusidens, Prochilodus lineatus, Salminus brasiliensis), as well as two potential mid-distance migrators (Parapimelodus nigribarbis and Pimelodus pintado). Although there is only one officially endangered species in the basin (S. brasiliensis), restricted range species (21.7% of total species) should be considered in conservation efforts.(AU)

Os ambientes aquáticos da Bacia do rio Taquari-Antas (Bacia da Laguna dos Patos, sul do Brasil) vêm sofrendo considerável transformação, principalmente em razão da implantação de barragens para geração de energia elétrica. Com o objetivo de estabelecer um diagnóstico amplo da ictiofauna da Bacia do Taquari-Antas, realizou-se um inventário das espécies dessa bacia a partir de dados primários e secundários. Foram obtidos 5.299 registros válidos de espécies de peixe na bacia, representando 119 espécies e 519 localidades amostradas. Ocorrem, na bacia, 13 espécies não nativas, seis das quais são oriundas de outras bacias neotropicais. Cerca de 24% de todas as espécies carecem de descrição taxonômica no nível específico. Foram registradas três espécies nativas migradoras de longa distância (Leporinus obtusidens, Prochilodus lineatus e Salminus brasiliensis) e duas potenciais migradoras de média distância (Parapimelodus nigribarbis e Pimelodus pintado). O fato de uma espécie ser oficialmente reconhecida como ameaçada na bacia (S. brasiliensis) e a grande proporção de espécies de distribuição restrita (21,7% do total) devem ser levados em consideração nos esforços de conservação.(AU)

Asunto(s)

RESUMEN

The state of conservation of Atlantic Forest in the Maquiné river basin was assessed using land cover data obtained from Landsat TM 5 satellite imagery (October 1995). The initial analysis examined the distribution of the relative areas of each land-cover type according to landscape slope classes, potential vegetation zones, and a 90 m riparian buffer. Land-cover classes were then regrouped into categories representing "low", "intermediate", and "high" degree of anthropogenic alteration. Results indicate that about 70% of the land cover of the Maquiné river basin has been highly altered as a consequence of replacement of natural forests by agriculture. Presently, a recovery process seems to be underway, contrasting with the historical trend towards deforestation. There are large areas of secondary vegetation in intermediate (34.8%) and advanced successional stages (20.2%), particularly across the range of the montane forest and of forest formations that occur at elevations higher than 800 m (high-montane dense ombrophilous forest and mixed ombrophilous forest). The geographical location at the southern limit of the Atlantic Forest stricto sensu and comparison of the results with data on the state of conservation of the Atlantic Forest in Rio Grande do Sul indicate that the Maquiné river basin is an important area for conservation. Some points regarding future research and conservation management are also discussed.

Asunto(s)

RESUMEN

O estado de conservação da Mata Atlântica na bacia do rio Maquiné foi avaliado com base em dados de uso do solo. As categorias de uso do solo foram identificadas a partir de uma imagem do satélite Landsat TM 5, de outubro de 1995. Inicialmente, a análise considerou a distribuição espacial das áreas relativas de cada tipo de uso do solo em relação às classes de declividade do terreno e às zonas de vegetação potencial em uma faixa ripária de 90 m. Posteriormente, os tipos de uso do solo foram reagrupados em categorias conforme o grau de antropização que representam: alto, intermediário e baixo. Os resultados indicam que cerca de 70% da área da bacia do rio Maquiné está, ou já foi, altamente alterada pela substituição da cobertura florestal por agricultura. Atualmente, parece haver um processo de recuperação da vegetação, uma vez que amplas áreas estão ocupadas por vegetação secundária em estádios sucessionais intermediários (34,8%) ou avançados (20,2%), particularmente na região da Floresta Montana e das florestas situadas acima de 800 m de altitude (Floresta Ombrófila Mista e Formação Alto Montana da Floresta Ombrófila Densa). A localização geográfica no extremo meridional da Mata Atlântica stricto sensu e a comparação com dados sobre o estado de conservação da Mata Atlântica no Rio Grande do Sul indicam que a bacia do rio Maquiné é uma importante área do ponto de vista de conservação. Alguns aspectos referentes à pesquisa científica e ao manejo também são discutidos.

Asunto(s)

RESUMEN

The age and growth of three silverside species are described, and a discussion on possible phylogenetic constraints on life-history characteristics is presented. Samples were collected monthly between March 1992 and February 1993 in three freshwater coastal lakes. Standard length-total length (Ls-Lt) and weight-length (Wt-Lt) relationships studied showed interspecific differences in comparisons between juveniles and adults, males and females. Age was determined by scales. The three species presented a life-cycle duration of 4 to 5 years, with growth coefficients values (K) between 0.37 and 0.63, and asymptotic lengths between 211 and 257 mm. Some interspecific differences may be useful for distinguishing between species (sexual and life-stage related patterns in Ls-Lt and Wt-Lt). The observed life-cycle ranges and maximum sizes were compared to those of other silversides and revealed a pattern coherent with available phylogenetic hypotheses at the supra-generic level, indicating that some life-history characteristics may be subject to phylogenetic constraints.

Asunto(s)

RESUMEN

The age and growth of three silverside species are described, and a discussion on possible phylogenetic constraints on life-history characteristics is presented. Samples were collected monthly between March 1992 and February 1993 in three freshwater coastal lakes. Standard length-total length (Ls-Lt) and weight-length (Wt-Lt) relationships studied showed interspecific differences in comparisons between juveniles and adults, males and females. Age was determined by scales. The three species presented a life-cycle duration of 4 to 5 years, with growth coefficients values (K) between 0.37 and 0.63, and asymptotic lengths between 211 and 257 mm. Some interspecific differences may be useful for distinguishing between species (sexual and life-stage related patterns in Ls-Lt and Wt-Lt). The observed life-cycle ranges and maximum sizes were compared to those of other silversides and revealed a pattern coherent with available phylogenetic hypotheses at the supra-generic level, indicating that some life-history characteristics may be subject to phylogenetic constraints.

Asunto(s)