Estudo dos efeitos de diferentes estratégias de pesca seletiva e da influência dos níveis

Abstract

This thesis work was conducted with the purpose of developing a multidisciplinary research by applying techniques of computational physics and statistics to problems coming from the areas of Biology and Ecology. Different aspects were investigated aiming to meet the needs of the fishing sector. Out of the fishes which have been undergoing the effect of selective fishing and of the alterations of the levels of fluctuation of the water in the rivers due to the building of dams, the surubim Pseudoplatystoma corruscans (Spix & Agassiz, 1829) stands out. Recently, Santos (2008) simulated the population dynamics of surubim subject to selective fishing by utilizing the selectivity curve based upon the current fishing legislation. According to the results obtained, selective fishing accounts for the possible alterations in the average growth rate, maturation age and length of the species. So, in the former part of this work, the population dynamics of the surubim taking into account different scenarios of mortality by fishing and their consequences on the population parameters were evaluated. From the results obtained in the simulations, it was found that selective fishing based upon the selectivity curves proposed is capable of causing evolution towards increasing the fishes growth rate, biomass and capture. These results suggest that changes in the current legislation are necessary to the sustainability of fishing and conservation of fishing stocks. In the latter part of that work, a study of the effects of the flush of natural flow and regulated by Três Marias dam - MG of the São Francisco River on the population and fishing production of surubim for twenty years before (1937-1957) and after (1983-2003) the establishment of Três Marias Hydroelectric Power Station. The results of the simulations reproduce efficiently aspects of the regularization of the river imposed by the functioning of Três Marias HPS such as interruption of the flood pulses and the alterations of the natural hydrological regime on the surubim’s population dynamics both with and without selective fishing, stressing that fishing production is strongly dependent upon the occurrence of flooding of marginal lagoons, its maintenance is fundamental to fishing activity. In this context, the management of fishing and of the river flow regulated is vital, for the trend of any fishing operational procedure in the unregulated HPSs is the one of collapsing.