Comparison of the population structure and dynamics of Aristeusantennatus (Risso, 1816) between exploited and unexploited areas inthe Mediterranean Sea

摘要

Data on the size distribution and population biology of the deep-water shrimp Aristeus antennatus were collected during four trawl surveys carried out along the Italian coasts (exploited area) and off north-western Greece (unexploited area). Comparison between the sampled populations was carried out in the 500-800 m depth range where trawl fishing, targeting deep-water shrimps (A. antennatus and Aristaeomorpha foliacea), occurs only along the Italian coasts. Some explorative hauls were also made as deep as about 1200 m. A. antennatus was collected down to 1122 m in the Italian area and 1174 m in Greek waters. It was found to be more abundant in the former area than in the latter. In both areas, the sex ratio was largely in favour of females and changed with depth. Maturity process by size was found to be similar in the two areas. Even though the median carapace lengths computed for the Greek samples were significantly greater than those for the Italian ones, a wide size range with superimposed modal components was found on both sides of the Ionian Sea. The estimated growth performance was the same in the two areas. In the Greek sampled population, the total mortality rates generally coincided with the natural mortality rates. No significant differences in the total mortality rates were detected between the Italian and Greek stock. The application of the yield per recruit model to the exploited stock, according to different scenarios, indicated conditions close to optimal harvesting. These results are discussed considering all the features which reduce vulnerability to fishing and favour recovery of the A. antennatus stock, thus blunting the differences in the population structure between the exploited and unexploited areas.