Avaliação da fauna acompanhante da pesca camaroneira e comparação entre as modalidades de arrasto de praia e arrasto motorizado na Paraíba, Nordeste brasileiro

Abstract

Despite the great socio-economic relevance, the fisheries cause changes of the ecosystem and populations. Trawl fishing is not very selective and captures a large biomass of bycatch, composed by fish, mollusk, echinoderms, crustaceans, and others. The artisanal shrimp fisheries carried through beach seining has great economic and social importance in the state of Paraiba. However, there is no information on the incidental catch of this fishery and its effects on the ecosystem. This study aims to evaluate the effects of shrimp fishing on the species of bycatch in Lucena (PB), in the Northeast of Brazil and makes a comparative analysis of the impacts of beach seining (BS) and motorized trawling (MT), which currently is prohibited by legislation. To describe the beach seining in Lucena, monthly samplings were conducted between December 2016 and November 2017. Ichthyofauna was identified and described in abundance in number and biomass. Specimens were measured and their size classes were correlated to the Size at first maturity (L50). Ichthyofauna was also described in the risk of extinction, using parameters of the International Union for Conservation of Nature and Natural Resources (IUCN) and they were classified considering feeding mode functional groups (FMFG) and estuary use functional groups (EUFG). The allometric coefficient was calculated for species with n exceeding 30 individuals that contained a satisfactory size range (33 species) of those 30 had negative allometric coefficient. A total of 199 kg (30.2%) of shrimp and 460 kg of fish (69.8%) were caught. The average catch proportion of target species and bycatch observed was 1:2.3. The bycatch was composed of 31.008 individuals of 11 orders, 36 families and 119 species. The most representative families were Sciaenidae, Pristigasteridae and Clupeidae, and the most expressive species were Opisthonema oglinum, Cetengraulis edentulus, and Pellona harroweri. The abiotic factors that most influenced this cycle of changes in the community were rainfall, flow and salinity and the species that varied most in abundance and/or biomass along this cycle were Lycengraulis grossidens, Menticirrhus americanus, Trichiurus lepturus, Chloroscombrus chrysurus e Cathorops spixii, Centropomus parallelus e Rhinosardinia bahiensis. According to the risk classification (IUCN), most (88) of the species were categorized as least concern (LC). A total of 66% of captured individuals did not reach sexual maturity (L50), indicating a high capture of juveniles. Considering the feeding functional group (FMFG), most species (61) were classified as zoobentivorous, indicating a higher susceptibility of species associated with the seabed. Regarding the use of the estuary (EUFG), the majority (49) were classified as marine migrant and marine stragglers (36), indicating the predominant migratory behavior in the captured species and the use of the coastal region as feeding and shelter area. The ecological indexes did not show a pattern of monthly or seasonal variation. Beach trawling captured a superior richness of species (AP 119; AM 58), while the proportion of bycatch was higher for motor trawling (AP 1:2,3; AM 1:3,2). The composition of ichthyofauna showed great similarity (81%), as well as the proportion of distribution of functional groups and the annual estimate of capture: shrimp (AP 87.9; AM 65.6 ton) and bycatch (AP 202; AM 210 ton). The similarities between these fishing modalities break a paradigm of low impact regarding beach trawling, whose effects are similar to motorized fishing in the different aspects approached.