Fish eggs and larvae drifting through hydropower reservoirs: a case study in the Brazilian Amazon

Ichthyoplankton drift is threatened by hydropower dams elsewhere. Here we evaluated whether eggs and larvae of fish can perform downstream movements along a large reservoir in a white-water river on the Amazon. Samplings were performed in the reservoir and downstream from Santo Antonio dam. Generalized linear models with negative binomial distribution and logarithmic link function were fitted to model the ichthyoplankton drift throughout the reservoir. Six different models were fitted having the abundances of ichthyoplankton as the response variable. The linear predictor differed as to the inclusion of the predictor variables larval development stage, sampling sites and dam distance (linear and quadratic effect). All ichthyoplankton and the most representative taxonomic orders were analyzed. The results indicate that fish reproductive activity occurred both upstream Jirau Dam and within the Santo Antonio Reservoir. Some part of the ichthyoplankton transposed the Santo Antonio Dam, reaching downstream. However, all of the taxonomic orders presented both reproductive activity and disappearance of at least some of their larval development stages along the reservoir. The most critical section was in the last 10 km of the reservoir, possibly as result of the drifting characteristics or of mortality rates.