Effects of migration activity on the mortality rates of two Portunidae crabs in a tropical bay

Abstract

Callinectes danae and Callinectes ornatus are two Portunidae crabs which are an important portion of the fishing products of Guanabara Bay, but are being discarded by shrimp trawlers along the Brazilian coast. Instantaneous mortality rates Z, M, F and the exploitation rates E for both species and for both sexes were estimated. Total mortality (Z) was estimated by length-converted catch curves and natural mortality (M) was based on life history analysis where K and t0 were parameters of the von Bertalanffy growth function. Fishing mortality rates presented low values of F for males of C. danae and C. ornatus (0.27 and 0.80), but not for the females (3.29 and 16.27). These females exhibited high values of fishing mortality and elevated exploitation rates (0.64 and 0.90). These high values may be a result of intense trawling in the region and/or the migration activity of these species to other coastal areas during the reproductive period, overestimating fishing mortality.