Stock size assessment and spatial distribution of bivalve species in the Gulf of Tunis

Abstract

The shellfish ranching, its current exploitation status and its management are becoming a major interest in fisheries industry in Tunisia. In this respect, the coasts of the Gulf of Tunis were explored along 20 shore-perpendicular transects to evaluate the stock size of shellfish populations. 285 samples of malacological fauna were collected by a VanVeen grab. This sampling revealed the presence of six target bivalve species owing to their high commercial value. The determination of the weight–size relationships of each species pinpointed that five species have a negative allometric relationship (Tellina planata, Tellina nitida, Glycymeris violacescens, Donax semistriatus and Solen marginatus) whilst Mactra stultorum indicated an isometric growth. The stock size assessment of these target species revealed that abundance values ranged from 2 to 60 individuals m−2, and biomass values varied from 2 to 230 g m−2. The mapping of the spatial distribution of density and biomass showed that the majority of species colonized essentially shallow waters corresponding to sandy and muddy bottoms. These findings are consistent with ecological and physiological properties of species. Major physical parameters influencing spatial distribution patterns are discussed.