Mapping stocks and population structure of the cockle Cerastoderma glaucum in the littoral zone of Sfax (Tunisia, Central Mediterranean)

The cockle Cerastoderma glaucum (Poiret, 1789) represents one of the most common marine mollusc species present in soft bottom infralittoral assemblages in southern Tunisian waters. The significant ecological role of C. glaucum in the ecosystem and its possible future commercial interest require a better knowledge of its stock. This study aimed to investigate the distribution, abundance and biology of these cockles within the Sfax region. Cockles were collected, treated and data were analysed. In terms of geographical occupation, maps of the population distribution were drawn. The results showed a scattered distribution pattern of the species according to location ranging between 0 and 256 ind.m(-2). The consequence was a remarkable biomass which represented 1596 +/- 697 tons of total fresh weight and high abundance levels reaching over 611 +/- 264 million individuals estimated in the area of 7120 hectares. The distribution of the species has also been investigated in consideration with the size which varied markedly according to sites, while the shell length ranged between 7 and 36 mm. The overall samples presented a balanced sex ratio, with males dominating among smaller individuals and females predominating in larger size classes. Males were found to mature between 12 and 20 mm shell length (SL), whereas females matured between 14 and 21 mm SL. The size at which 50% of the population reached maturity was 15.14 and 16.78 mm SL for males and females, respectively. Findings of the current study suggest that C. glaucum well proliferates in southern Tunisian waters.