Alteration of Fish Diversity Downstream from Petit-Saut Dam in French Guiana. Implication of Ecological Strategies of Fish Species

Abstract

Dams are expected to decrease fish diversity because they deeply alter downstream environment. However, such decline has not been consistently observed although profound modifications in the structure and/or composition of fish communities were generally recorded, and were linked to modifications of the downstream environment. In this work we analyze data from observations made before and almost 10 years after the completion of a hydroelectric dam in the neotropics. We monitored fish diversity below that dam and compared the taxonomic and functional structures of the samples between the pre- and post-dam periods. A significant decrease in species richness was evidenced. Taxonomic and trophic structures were significantly different between the two periods. Conversely, the functional structure of samples based on reproductive traits did not change significantly after the damming. Concerning feeding habits, a large increase in relative abundance of detritivores and a parallel decrease of fish species feeding on terrestrial food sources were observed in samples taken 6–9 years after closure of the dam as compared with samples taken before the dam.