Catch rate for the skipjack tuna (Katsuwonus pelamis) in the Southwest of the South Atlantic Ocean

Abstract

Catch rates may be used as abundance indices of populations exploited by commercial fishing fleets. However catch rates must reflect temporal trends of the biomass and they could not be biased due to factors such as changes in the coefficient of vulnerability. In this paper, generalized linear models were used to estimate catch rates of skipjack (Katsuwonus pelamis) caught in the southwest of the South Atlantic Ocean. Gamma density function and logarithm link function were used to model the variable of interest. The coefficient of variation as calculated for the annual catch rates were all close to 0.15. The variations of the catch rates did not show time trends. Therefore the biomass of the population probably did not change much in the last twenty years.