Artisanal fisheries in a Brazilian hypereutrophic reservoir: Barra Bonita reservoir, middle Tietê river

摘要

This study examines the qualitative and quantitative aspects of fishery landings at the hypereutrophic Barra Bonita reservoir, Brazil. Data were collected each month (July/2004-June/2006) at three localities and the reported catch, fishing effort and fishing techniques were recorded from 745 landings, comprising a total fish catch of 86,691.9 kg. The most caught species were exotic tilapias, especially the Nile tilapia (Oreochromis niloticus L.), which represented 82.5% of the total biomass. The reservoir's fishery productivity was 11.1 kg/ha-1/day-1 with a Catch Per Unit Effort of 62.4 kg/fisher-1/day-1. Five fishing techniques were identified: cast net, gill net, trawl net, beating gill net, and beating gill net + gill net. The analysis of DCA related the active strategies for the tilapia catch, to the passive strategies for the Pimelodus maculatus (Lacepède) and Triportheus angulatus catches (Spix & Agassiz), and the mixed strategies for the tilapia, catfish and Prochilodus lineatus (Valenciennes) catches. ANCOVA results were significant for all the variables analysed (season, fishing location and fishing technique). The results showed that fishing for "corvina" Plagioscion squamosissimus (Heckel), predominant in the 1990s, had been replaced by fishing focused on the Nile tilapia. This substitution appears to be due to the increasing levels of eutrophication in the reservoir, combined with changes in fishing techniques. The pattern of the fisheries in Barra Bonita Reservoir follow those in other eutrophic Brazilian reservoirs, with catches of the exotic Nile tilapia predominating.