Distribution and Abundance of the Mantis Shrimp Squilla mantis (Crustacea: Stomatopoda) in Tunisian Waters: Gulfs of Tunis, Hammamet and Gabes

The mantis shrimp Squilla mantis is a crustacean Stomatopod of the family of the Squillidae. This specie is found in high densities in areas with suitable burrowing substrates in the Mediterranean Sea. The objectives of the present study were to characterize the distribution and the abundance of the spot-tail mantis shrimp caught in Tunisian waters. The Spot-tail mantis shrimp is exploited in this area and it is still considered as a bycatch, but its abundance makes it important for fisheries. Information about distribution, abundance and size composition of the Squilla mantis were obtained from trawl surveys, carried out in the Tunisian Gulfs monthly for a period of two years. A total of 643 hauls were made and 22,878 specimens were captured. This study shows that this mantis shrimp is very abundant in the Tunisian waters, especially in the Gulf of Tunis, Hammamet and Gabes. S. mantis has a wide geographic distribution, since it was collected in all the major areas investigated, but differences were highlighted among the geographic sectors sampled. Maximum abundances occur shallower than 50 m depth. The values of the catches vary seasonally, the highest of which occurring in summer and autumn. Adults disappeared from the population during winter whereas females do not exit their burrow during incubation. The variability of the catches is due to the effect of several factors such as the effect of month, season, depth, hour, luminosity, weather... This specie is more closely related to crustaceans, cephalopods and benthic fish’s. According to the depth, no variation in length distributions of Squilla mantis is observed. The fact that egg-bearing females do not exit their burrow during incubation makes the catch ability lower during day-time. Trawling as well is not permitted shallower than 50 m in the Tunisian waters which may protect these species from fishing.