Influence of deforestation on fish diversity and biomass in the Amazon River
Despite considerable attention garnered by recent estimates of deforestation in the Amazon, the influence of forest cover on fish communities in Amazonian rivers and floodplains remains undocumented. To examine relationships between forest cover and fish diversity and biomass, we conducted extensive field surveys of landscapes, aquatic habitats, and fish assemblages within the floodplains (“varzea”) of the Lower Amazon River. Surveys were conducted during four phases of the annual flood cycle within 126 habitats across 17 lake systems along a gradient of landscape impacts (from relatively pristine forest to areas deforested for livestock grazing). Here we report results for the high-water period. Fishes were sampled using gillnets of varying mesh sizes in order to capture a broad range fish species and body sizes normally harvested in regional fisheries. For each sampled lake system, floodplain vegetation cover was quantified using GIS. We analyzed fish abundance (biomass catch-per-unit effort, CPUE) patterns of fish species and trophic guilds in relation to percent forest cover of local watersheds.
Significant positive relationships were found between fish abundance and forest cover across geomorphologically-defined landscape units, and also between fish abundance and aquatic habitat categories. Median CPUE for herbivorous fishes, a group that includes some of the most economically valuable species, was 1.8 times higher in pristine areas than in deforested areas. These results and our ongoing research highlight the need to study impacts of land use, including deforestation, on fish ecology in the Amazon. Future analyses of fish assemblage structure, food web ecology, and local fishing activities and management will be integrated to explore relationships between ecological and social factors.