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Univariate diversity indices and multivariate analyses (cluster and multidimensional scaling (MDS) were performed in order to evaluate biodiversity in two neighbouring areas of the Eastern Mediterranean with different fishing intensity. Data were collected from two trawl surveys (July and August 2000) in two areas of the Ionian Sea. In the area off the South-eastern Italian coast, there is a trawl fishery at depths between 300 and 700 m that targets the deep-sea shrimps Aristeus antennatus and Aristaeomorpha foliacea. In the other area off Northern Greece, fishing is only carried out down to 400 m depth.While diversity indices did not show convincing differences in the community structure between the two study areas considered as a whole, the multivariate analysis showed a clear pattern linked to depths and areas highlighting the distribution of abundance of the various species. Depth played the main role in the group differentiation, indicating the existence of two quite distinct bathyal faunal assemblages: one on the upper slope, the other on the middle slope. The results of the geographic characterization of the diversity and of the assemblage composition are discussed considering the different fishing intensity as well as the environmental conditions in the two areas of the same basin.

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Gear selectivity and discards are important issues related to fisheries management but separately modelled. This work examines for the first time the overall size-selection pattern on the total amount of individuals of a species entering the trawl codend. An innovative approach was used based on modelling the escapement through the codend in the sea and the subsequently selection process by the fisher on the deck of the fishing vessel resulting into the discards and landings. Three different trawl codends and three species were investigated in the case study conducted. A dual sequential model accounting for both gear size-selectivity and the subsequent fisher-size-selectivity was applied, under the hypothesis that a fish entering the codend can follow a multinomial distribution with three probabilities, the escape, the discard and the landing probability, respectively. The model described the escape probability through the gear and the landing probability by the fisher as S-shaped curves leading to a bell-shaped curve for the discard probability affected by both gear and fisher selection. The model described well the experimental data in all cases. Sampling scheme of three compartments proved adequate. The model provides at the same time selectivity and discards parameters useful in fisheries management.