Stock assessment, spatial distribution and biological parameters of the clam Venerupis decussata along the Sfax coasts (Tunisia, Central Mediterranean)

Abstract

The grooved carpet shell Venerupis decussata (=Ruditapes decussatus) (Linnaeus, 1758) is a Mediterranean autochthonous species that in Tunisia is heavily harvested from natural populations. It represents one of the important economic issues, especially in terms of employment and the trade balances of the country via its exportation. Despite its economic value, no studies have been carried out about the spread of this mollusc. Thus the status of this species is still poorly known and there is a knowledge gap about its stocks assessment. This study aimed to investigate the distribution, abundance and population structure of the carpet shell clam in Sfax coastal areas. In terms of geographic 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 152 ind m−2. The consequence was a remarkable biomass which represented 891 tonnes of total fresh weight and high abundance levels reaching over 261.7 ± 84.2 million individuals estimated in the area of 4182 hectares. The distribution of the species has also been investigated in consideration with the size which varied markedly according to location, the shell length ranged between 2 and 41 mm. The overall sex ratio (F:M) was 1:1.17, which was significantly different from parity (1:1). The size at which 50% of the population reached maturity was 24.08 and 24.76 mm shell length for males and females, respectively. Findings of the current study suggest that V. decussata proliferates along southern Tunisian coasts.

Stock mapping, size structure and biological parameters of the clam Polititapes aureus in the shellfish production area of the southern Tunisian waters (Central Mediterranean)

“…The bottom slopes slightly toward the sea, with a depth of 60 m occurring 110 km off the coast (Ben Othman 1973). The substrate in the inshore area is mainly silty sand (Derbali et al 2016) covered in some places with the seagrass Cymodocea nodosa (Ucria) Ascherson and Zostera noltei Hornemann. The littoral zone of Sfax is characterized by a benthic community of an exceptional bionomy, consisting of extensive meadows of magnoliophytes Posidonia oceanica and C. nodosa (Ben Mustapha & Hattour 2013).…”

Multiannual trends of toxic and potentially toxic microalgae (Ostreopsis cf. ovata, Prorocentrum lima, and Coolia monotis) in Sfax coasts (North of Gabes Gulf, Tunisia)

“…Sfax coasts stretch approximately 85 km from the fish harbor to Skhira. The substrate in the inshore area was mainly muddy sand (Derbali et al, 2015). The tide was semidiurnal, with a high tide of +1.60 m and a low tide of +0.30 m (Zaghden et al, 2014).…”

“…The inshore southern coasts of Sfax were an important exploitation area of the grooved carpet shell (Ruditapes decussatus, Linnaeus, 1758) in the Gulf of Gabes with 79% of the total Tunisian production (Ben Naila et al, 2012). These bivalve populations can be found in sandy and muddy-sand sediments in bays, estuaries, coastal lagoons, and other sheltered environments, living on tidal flats and below tidal marks (Derbali et al, 2015).…”

Morphometric Variation among Four Local Ruditapes decussatus Populations in Monastir Bay (Eastern Coast, Tunisia)

“…It represents an important economic endpoint since it is a natural resource and has a high commercial value [11]. Many studies have been conducted on R. decussates from different regions in Tunisia from the perspectives of biology [12,13], ecotoxicology [14][15][16] and stock assessment [17].…”