CVPA, an expanded VPA with cannibalism. Application to a hake population

Abstract

A generalized method of VPA, called CVPA, including the effect of cannibalism is presented. In this method, natural mortality was split into two components, one depending on cannibalism and the other, which remains constant, due to all other natural causes. These are not evaluated, but the method enables us to include new mortality causes when they are quantified.

This method was applied to Cape hake (Merluccius capensis) off the coast of Namibia, from latitudes 25 to 30°S. The results were compared to the values obtained using the standard VPA. Significant differences in number of fish at any given age and natural mortality were found between these two methods, showing that standard VPA underestimates the values for the youngest age groups. Biomass levels at a given age show the same trend somewhat attenuated