Modelos lineares generalizados no estudo de proporções de agulhões vela (Istiophorus albicans) e verde (Tetrapturus pfluegeri) na pesca de atuns com espinhel no oceano Atlântico

Abstract

The reliability of catch data of the pelagic logline fisheries is of concern especially for non-target species like sailfish (Istiophorus albicans) and spearfish (Tetrapturus pfluegeri). The catch of those two species is often reported aggregated hence it is difficult to calculate separated catch of each species. In this work the objective was to build a generalized linear model to estimate the proportion of sailfish (or spearfish) when the catch are aggregated. The response variable (number of sailfish in the aggregated catch) was assumed to follow a binomial distribution. Explanatory variables were year, quarter, fleet, distance from equator and distance from coast. Logit was used as link function. Models were selected for different scenarious as defined based on the inclusion or exclusion of factor year and fleet. Models fittings were ecceptable in the sense they are not biased. Sensitivity analyses were carried out because some influential data appeared. Variables fleet, quarter and distance from the equator and from coast are important to explain the variation of the sailfish proportion. China Taipei and USA fleet catches show high proportion of sailfish. The proportions in the north and south hemispheres are high in the boreal and austral summer respectively. The proportions are also high in the equatorial and regions.