Ecologia e conservação de peixe anuais em áreas úmidas temporárias no Sul do Brasil

Abstract

In the present study, we used two approaches. At the local scale we studied the fish community of temporary wetlands along a hydrological cycle. At a regional scale we investigated the patterns of diversity and conservation status of species of annual fish of Rio Grande do Sul. In the first approach we aimed : (1) to assess the spatial and temporal variation and environmental factors that affect the fish community of temporary wetlands, (2) to analyze temporal variations in size, specific growth rate and density of three annual fish species, and (3) to analyze the length-weight relationship of these same species. Therefore, we collected fishes monthly throughout one hydrological cycle in 11 temporary wetlands in the São Gonçalo floodplain, South Brazil. The composition and abundance of fishes showed marked spatio-temporal variation associated with differences in the life cycle of the species. Annual fishes comprised the most abundant group and were resident throughout the hidrological cycle. The composition and abundance of fishes in these areas were influenced by habitat and landscape variables (area, number of microhabitats and isolation), climate and hydrological variables (hydroperiod, average rainfall and level of São Gonçalo channel) and physical (wetland depth). The three annual fish species showed similar population dynamics. They all hatch at the beginning of flooding and die off as the wetlands dry out. The annual species showed similar specific growth rates but different body sizes, which ensures that the differences in body size between them remain constant throughout the hydrological cycle. These species have two patterns of growth, allometric positive and negative. We found a high diversity of annual fishes at the regional scale. We recorded 37 annual fish species belonging to genus Austrolebias (31 species) and Cynopoecilus (6 species) in samples performed in 50 municipalities of Rio Grande do Sul. Most species have restricted distributions and are threatened of extinction due to agricultural practices and urban advancement. Conservation strategies for the species, in turn, depend on a number of factors and initiatives, but in general are related to encouraging research, search and mapping of species, definition of taxonomic problems, correct environmental licensing, environmental education and a great incentive plan and encouraging of the creation of protected areas.