Temporal dynamics of size spectrum of a fish population in neotropical reservoirs

Studies on the size spectrum allow indirect inferences of how the energy flows from one organism to another. Assuming that the bottom-up is more intense than the top-down mechanism along the cascade of reservoirs, which limits the growth and development of individuals, we investigated the effect of a cascade of reservoirs in a neotropical basin on the stock and distribution of the population of Oligosarcus longirostris, a species at the top of the food chain. Samples were conducted quarterly in five reservoirs, from March 2004 to December 2008. Stock size was estimated by catch per unit effort (CPUE); to establish the size spectra slopes of fish, we used Pareto I model, and data was analyzed using univariate analysis of variance followed by Tukey's test. There was a higher proportion of smaller individuals in the first reservoir of the cascade, with a decline in this proportion along the succession of reservoirs in the cascade. It can be concluded that there is an effect of the reservoir cascade on the abundance and size of individuals of Oligosarcus longirostris.