Effects of reservoirs water level variations on fish recruitment

ABSTRACT The construction of hydroelectric power plants has many social and environmental impacts. Among them, the impacts on fish communities, which habitats are drastically modified by dams, with consequences across the ecosystem. This study aimed to assess the influence of water level (WL) variations in the reservoirs of the Itá and Machadinho hydroelectric plants on the recruitment of fish species from the upper Uruguay River in southern Brazil. The data analyzed resulted from the WL variation produced exclusively by the hydroelectric plants generation and were collected between the years 2001 and 2012. The results showed significant correlations between the abundance of juvenile fish and the hydrological parameters only for some reproductive guilds. The species that spawn in nests showed, in general, a clear preference for the stability in the WL of the reservoirs, while the species that spawn in macrophytes or that release demersal eggs showed no significant correlation between the abundance of juvenile fish and hydrological parameters. A divergence of results between the two reservoirs was observed between the species that release semi-dense eggs; a positive correlation with a more stable WL was only observed in the Machadinho reservoir. This result can be driven by a wider range of WL variation in Machadinho reservoir

Temporal variability of fish larvae assemblages: influence of natural and anthropogenic disturbances

Natural and induced disturbances greatly influence the temporal distribution of ichthyoplankton abundance. This study assesses and compares the temporal variability of fish larvae assemblages in controlled and free environments to determine the influence of environment variables on the main taxa in these systems. The study was conducted at the Chapecó (without dam impact) and Ligeiro (with dam impact) river mouths, which are located in the upper Uruguay River. Samples were made between October 2001 and March 2004 during three reproductive periods. The larvae assemblages were composed of small and medium-sized Characiformes and Siluriformes. The variation in the distribution of larvae was mainly temporal (>85%). When the three reproductive periods were compared, it was observed in the second period, characterized by a larger water flow and a lower temperature, that there was a reduction in abundance, a lower number of taxa, an absence of stages in post-flexion and a high dissimilarity in larvae assemblage structure. In general, the environmental variables of water flow and temperature most influenced the distribution of egg and larvae abundance. In the studied area, a smaller temporal variability was observed in the structure of larvae assemblages at the sampling sites in the Chapecó River mouth than in in the Ligeiro River mouth under the influence of dams

Spawning of migratory fish species between two reservoirs of the upper Uruguay River, Brazil

This study investigated the migratory fish spawning within the reservoirs of the Machadinho and Itá dams (upper Uruguay River, Brazil) and its relationship to environmental variables. Sampling was conducted in the lotic region of the river in two sites between the dams' reservoirs: Uruguay (main river) and Ligeiro (tributary). Sampling included nine consecutive reproductive periods (RP) spanning the period from 2001 to 2010 and was conducted at night on the water surface using cylindrical-conical plankton nets (0.5 mm mesh); environmental variables were also recorded. The spawning of the migratory species Salminus brasiliensis, Prochilodus lineatus, and Steindachneridion scriptum was registered: S. brasiliensis and P. lineatus spawned in the tributary river at the end of spring/beginning of summer, during flooding and during periods of high water temperature. Steindachneridion scriptum spawned in the main river at the beginning of spring. The study showed that S. brasiliensis, P. lineatus, and S. scriptum are able to spawn in small lotic river stretches within two reservoirs, but only under very specific and not common environmental conditions