SPACE-TIME VARIATIONS OF DEMERSAL FISH ASSEMBLAGES IN THE SOUTH-WESTERN ADRIATIC SEA

The authors analysed qualitative and quantitative data from trawl-surv eys, carried out to estimate demersal resources distribution and abund ance on South-Western Adriatic bottoms (Mediterranean Sea), in order t o evaluate the differences in fish assemblages over time and space. In the mentioned area four seasonal trawl-surveys were carried out in 19 91 and 1992 using a professional trawler (400 Hp), equipped with an '' Italian'' trawl net (36 mm stretched mesh at cod-end); twenty five fix ed stations were sampled for each survey. Fish species qualitative (pr esence/absence) and quantitative (abundance index) data were performed by means of multivariate analysis (Cluster analysis, Multi-dimensiona l Scaling). The results show small differences in the fish assemblage distribution among the four surveys; few sampling stations seem to be affected by seasonal variations (stations between 0 and 50 m depth and at the lower limit of the photic zone). The fish assemblages referrin g to the remaining stations appear to be almost constant over time in relation to some constant parameters like depth, substratum etc.; the hypothesis is confirmed by the analysis of environmental published dat a related to the sampling area.