Overfishing ofmarine resources: some lessons from the assessment

The recent, rapid development of fishing inMauritania offers a good case study for a comparative approachof the resilience of the species exploited there, in the face of increasing fishing pressure. First, we assessed the health of 22 demersal stocks with differing ecological requirements, demo-graphic strategies, and states of exploitation. A dynamic production model was fitted in a framework of Bayesian statistics to abundance indices estimated from scientific trawl surveys or commercial catch per unit efforts. We show that 12 of the 22 stocks assessed are overexploited and 3 are fully exploited. The combined assessment of all 22 stocks demonstrates an overall overexploitation, with total demersal biomass decreasing by 75 % since 1982 and fishing effort 30 % higher than that at maximum sustained yield (40 % higher for finfish). Second, relations between states of stocks and life history traits were analysed. The stocks of large and vulnerable species currently undergo the highest fishing pressure and are those that are the most overexploited. At the scale of the community represented by the stocks considered, surveys-based indictors of the mean intrinsic vulnerability, the mean maximum length, and the mean trophic level exhibit a significant decrease from 1990 to 2010. Changes observed in catch-based indicators depend on fishing strategies and are impacted by the recent development of the small-scale fishery. But indi-cators expressed as a function of a multiplier of fishing effort or fishing mortality clearly decrease, thus confirming that the intensification of ex-ploitation leads to communities dominated by smaller species and lower trophic levels.We conclude that large and high trophic level species, suc