Spatial and temporal variation of fish eggs and larvae in a cascade of small hydropower plants in south-eastern Brazil

Context Studies focusing on ichthyoplankton distribution are important tools for the establishment of conservation actions, including the management of fish stocks. Aim To investigate the distribution of ichthyoplankton in a reservoir cascade of three small hydropower plants in the Sapucaí-Mirim River, south-eastern Brazil. Methods Six sampling sites were distributed in the river stretch under the direct influence of the most upstream and downstream dams. Samples were collected fortnightly between November and February (spring–summer) in 2015–2016 and 2016–2017. Key results In total, 5004 eggs (unidentified) and 3189 larvae belonging to 4 orders and 15 families were sampled. Temporally, higher densities of eggs and larvae occurred during periods of increased rainfall and associated changes in environmental variables. Spatially, higher densities of eggs were observed in the most upstream reservoir, in the lotic (2015–2016) and transition (2016–2017) zones. For larvae, abundance was higher in the transition zones. Conclusions The study demonstrated that the small hydropower plants reservoir cascade is not an impediment to fish spawning and the drift of eggs and larvae, including important migratory fish species from the river basin. Implications This stretch of Sapucaí-Mirim River is a critical area for fish recruitment and efforts to preserve it are necessary.