Bioeconomic analysis of the Mauritanian cephalopods fishery

Cephalopods represent a very significant fishing resource in Mauritania. In particular, Octopus vulgaris (Cuvier 1797) whose value increases according to weight is the most valuable species. The resource shows significant inter annual variations in abundance related to the varying environmental conditions off Mauritania and the previously conducted species stock assessments indicate a state of overexploitation and growth over fishing. A bioeconomic single species population dynamics model is developed to estimate the combined impact of fishing closure duration and timing and minimum size at capture in various hypothetical exploitation scenarios to the yearly yield, value of yield and spawning stock biomass. Applying monthly cohort analysis in a Bayesian framework using MCMC sampling enabled us to implement the model with the variability observed in seasonal and inter annual environmental conditions and the uncertainty related to different aspects of the species biology. The currently applied management measure, a two-month closing season in September-Oct ober with a minimum size at capture of 500 g, is used as the reference point. The results indicate that the current timing of the closed season is optimal and no considerable gains in value of yield are obtained using other timings. However, increasing the minimum size at capture seems to be profitable. For example, minimum size of 1000 g with a two-month closing season in September-Oct ober yields a mean relative gain of 16 % in yearly value of yield. The findings of this study will contribute to the sustainable use of cephalopod fishery resources in Mauritania by providing indicators for the economically optimal harvest of the species. The methodology applied in this study aims to be applicable also to other cephalopods fisheries. This paper was prepared as part of EU 6 th framework programme project “Probabilistic assessment, management and advice model for fishery management in the case of poor data availability” (POORFISH), contract no. 22745.