Venerupis decussata (Linnaeus, 1758) (Mollusca: Bivalvia) in southern Tunisian waters: distribution, abundance and biological parameters

Venerupis decussata represents one of the most common marine mollusc species present in soft bottom infralittoral assemblages in southern Tunisian waters. It is a Mediterranean autochthonous species that in Tunisia is heavily harvested from natural populations. This bivalve represents an important economic issue, especially in terms of employment and the trade balances of the country via its exportation. The status of this species is still poorly known and there is a knowledge gap about its abundance. The present work aimed to investigate the stock assessment, the population structure and to give some biological parameters of V decussata along the Gabes coastal area. The main results showed a scattered distribution pattern of the species according to location ranging between 0 and 26.6 ind.m(-2). A remarkable stock was estimated to be 2405 tons (total fresh weight), with a mean biomass around 52.5 g.m(-2) and a total abundance reaching an estimated 908.8 million individuals in the investigated area of 4577 hectares. Shell length of sampled individuals ranged from 4.2 to 41.65 mm, and median size varied by location. The overall sex ratio (F:M) was significantly different from parity (F:M = 1:1.17, chi(2)-test, P < 0.001). Males were found to mature between 22 and 27 mm shell length (SL), whereas females matured between 22 and 28 mm SL. The size at which 50% of the population reached maturity was 24.08 and 24.76 mm SL for males and females, respectively. Overall, V decussata proliferates in some portions of the study area.