Effects of a change in mesh size on Nephrops stocks in Portuguese waters

Abstract

An assessment of the effects of a change in mesh size on the Alentejo and Algarve Nephrops norvegicus L. stocks, based on the method of length-cohort analysis is presented in this work. Since Nephrops cannot be aged, this model is suitable because it uses length rather than age classes; analytically it is based on a procedure similar to age-cohort analysis. The analysis shows that provided instantaneous natural loss ( M) is less than 0.42, an increase in mesh size to 80 mm should lead to long-term gains in yield per recruit and biomass per recruit in both stocks. Overall the magnitudes of these gains are about 90% in the case of biomass and 27% in the case of yield per recruit for females and males combined.