Evolution of the fish assemblage around a gas platform in the northern Adriatic Sea

Effects induced on the fish assemblage by the gas platform "Regina", installed in October 1997 in the northern Adriatic Sea (depth 21 m), were investigated by monthly sampling with a trammel net near the platform and at open-sea control site. Total catch rates did not differ appreciably between the two sites. However, the fish assemblage near the platform showed greater species richness and a higher Shannon-Wiener diversity index, mainly owing to the presence of reef-dwelling or partially attracted benthic and nekto-benthic fishes that are less common in the natural local sand-muddy bottom habitat. Similar seasonal patterns were observed at the two sites in terms of number of species, diversity, and total catch rates, with lowest values recorded in winter/spring. In terms of temporal evolution, number of species at the platform increased rapidly during the first year after deployment, followed by a levelling off in subsequent months. In contrast, catch rates obtained for different categories of species indicate a longer development time in terms of number of individuals and biomass.