Exploitation status and stock assessment by pseudo-cohort analysis of the gilthead seabream Sparus aurata in the Gulf of Gabes (Tunisia)

The gilthead sea bream, Sparus aurata, is quite abundant in the Gulf of Gabes, off the south-eastern coast of Tunisia. It is commercially exploited by artisanal gears and trawlers all year round. Catches of gilthead, in the period 20002010 fluctuated between 145.3 t and 241.9 t (except in 2008) with an annual average of 204 t. The analysis of the virtual population of gilthead sea bream in the Gulf of Gabes showed that, in 2008, the stock was subject to a fishing effort (348 t) that passed its capacity (E = 0.61 > 0.5). The biomass (B) estimated to be 850.4 t only tolerated the extraction of 338.4 t (more or less one-third of B). As a result of this over-fishing, the actual stock of gilthead sea bream in the Gulf of Gabes was characterized by individuals having a mean total length of 17.2 cm, a size which is much lower than the one at first sexual maturity (18 cm). The turnover (D/B) being of 54%, it did not allow the reconstitution of the stock. The total removals (626.7 t) due to both natural mortality (M = 0.34) and fishing mortality (F = 0.542) had to be compensated especially by individual growth (529.3 t, 84.46%) because of the low weight of the recruits.