A pesca artesanal no reservatorio Billings (São Paulo)

AUTOR(ES)
DATA DE PUBLICAÇÃO

1997

RESUMO

Billings reservoir is the largest water body in the Metropolitan Region of São Paulo. Its building started in 1925 in order to supply the city of São Paulo with electricity. During many years it presented low environmental quality due to the reception of organic sewage from the Metropolitan Region. Nowadays, it is used also as an outlet regulatory system from High Tietê Basin, as water source and as leisure area. An intense artisanal fishery activity is developed. with 101 active fishermen. The objectives of this study are to describe the fishery, to evaluate the catch composition in weight, to evaluate the effort with different gears and to examinate the factors that could explain the catches. Landings were recorded daily from February 1996 to January 1997, at Colônia (São Paulo city). During this period 147.593 kg of fish were caught in 3.515 fishing trips by 21.5 fisherman/month in average, with mean yield of 42 kg/trip and 572 kg/fishermen/month. The main commercial species caught were Nile tilapia Oreochromis niloticus (81.4% of landings in weight). "lambari" Astyanax eigenmanniorum (13.0%), common carp Cyprinus carpio (2.4%), "traíra" Hoplias malabaricus (2.1 %), "sagüiru" Cyphocarax modestus (1.1 %) and catfish Rhamdia sp (0.1 %). The fishing gears used were gillnets, cast nets and gillnets used in an active way ("redes de batida"). Nile tilapia are caught with cast nets and gillnets "redes de batida". The other species are caught with gillnets. The fit of a linear covariance model on Nile tilapia catch and effort data showed that the effect of the fishing ground was the only important factor to explain the catches discounting the effect of the covariate fishing effort. Neither the month nor the fishing gear explained a significant portion of the variability. In the final model, effort explained 91.14% of the total variability and fishing ground explained only 3.27 %. The fishing grounds with highest catches were Pedreira and Alvarenga, near Pinheiros river pumping station. To explain this result three hypotheses are discussed: high capturability, high productivity, and fishermen strategies. The low richness and high dominance of few species on landings are indicative of communities under stressing conditions, which in the Billings case are: transformation of a lotic ecosystem in a lentic one, eutrophication, contamination and introduction of exotic species. The dominance of Nile tilapia is attributable to a combination of factors such as high resistance to low dissolved oxygen contents, tolerance to chemical stressors, ability to consume plankton and existence of a developed littoral zone enabling Nile titapia s nesting

ASSUNTO(S)

ecologia reservatorios pesca artesanal

ACESSO AO ARTIGO

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