Fish defaunation in reservoirs of the Lower Paranapanema River basin, Brazil

Abstract

Until now no study has used a defaunation index to quantify the decline of Neotropical freshwater fishes in environments fragmented by dams and reservoirs. So, we applied this index to 143 native fish in five reservoirs in the Lower Paranapanema River, that is situated in one of the Brazilian aquatic environments most impacted by anthropic degradation. Fish species were classified according to their functional groups, which were selected according to the biological characteristics that may reflect in defaunation events. The biggest reservoir in area with more tributaries and forest cover showed lowest defaunation index. The functional groups of fishes more affected by defaunation included species characterized by periphytivores, invertivores and algivores, non-migratory habit, with external fertilization, and parental care. Although reservoirs have different characteristics, this method can be tested in any other hydrographic basin. The results suggested continued conservation efforts to preserve the integrity of tributaries and the native fishes in reservoirs and pointed out the importance of maintaining native vegetation cover and fish restocking programs in the reservoirs with the highest defaunation values. Our finding can be use as the first data source for future studies using this defaunation index.

Vetores de mudança diretos e indiretos que afetam a introdução, o estabelecimento e a disseminação de espécies exóticas invasoras

“…Todavia, experimentos realizados em mesocosmos revelaram que a redução da transparência da água e na abundância de piscívoros nativos pode favorecer a invasão por espécies de peixes exóticos invasores, como o tucunaré, a tilápia e o bagre-do-canal (Ictalurus punctatus) na bacia do rio Paraná (Santos et al 2018). No Rio Paranapanema, o declínio de peixes neotropicais foi relacionado a ambientes com barragens e reservatórios e pouca cobertura florestal (Barros et al, 2023). Porém os autores destacam a necessidade de analisar outras variáveis que possam contribuir para a defaunação ou a combinação sinérgica delas, como por exemplo, a presença de EEIs.…”