Fish species biodiversity on trawlable bottoms of South Adriatic Basin (Mediterranean Sea)

Groundfish biodiversity on trawlable bottoms of the South Adriatic basin was analysed by means of univariate ecological indices. Raw data came from three experimental trawl surveys carried out in the mentioned area during the summer 1996, 1997 and 1998. The surveys (112 samples per survey) provided a total list of 113 groundfish species (98 teleosts, 15 selachians). Margaleff (richness), Shannon (diversity) and Pielou (evenness) indices were estimated; the index values per sample were mapped by kriging method, and mean values for each survey were computed in order to detect yearly and/or spatial differences (shelf and slope zone, East and West coast). The global analysis of the diversity of the groundfish species on the trawlable bottoms of the South Adriatic Sea did not show any particular trend over the triennium 1996-98, in spite of some significant differences among the years. The main changes concern the "shelf" ecological indices, while the "slope" situation appears to be reasonably stable; East (Albania) "shelf" values are generally higher and more homogeneously distributed than the West shelf (Italy) ones.