Comparison of the Dynamics between Coastal and Midshore Populations of Pinctada radiata (Leach, 1814) (Mollusca: Bivalvia) in the Gulf of Gabes, Tunisia

Pinctada radiata is the first lessepsian bivalve in the Mediterranean Sea where it has, been progressively expanding westwards. This comparative study provides the first insight into the population dynamics of the species by investigating the population, structure, growth, mortality, and exploitation status in the coastal zone (site A; 0-1 m) and midshore area (site B; 14 m depth). The results showed that the asymptotic shell length was smaller in the coastal zone (L∞ = 78.75 mm) compared to that in the midshore station (L∞ = 105 mm). Growth coefficient (K) was higher in site A (1.70 yr-1) than in site B (0.66 yr-1). Growth performance index (Φ') values were almost similar (4.023 and 3.862) in both pearl oysters stocks. The theoretical maximum age (Tmax) was smaller in site A (2.66 yr-1) than in site B (7.05 yr-1). Total mortality (Z) was estimated by length-converted catch curve at 6.18 and 1.62 yr-1, fishing mortality (F) at 4.43 and 0.78 yr-1 and natural mortality (M) at 1.75 and 0.83 yr-1 for site A and site B, respectively. Recruitment was continuous and showed two major pulses in the two sampling sites.