Temporal and spatial variation of the fish assemblage around a gas platform in the Northern Adriatic Sea, Italy

The "Barbara NW" platform, located in the northern Adriatic Sea 56 km offshore and at 68.5 m depth, was monitored for investigating the temporal and the horizontally spatial extent to which the gas platform attracted different fish species during the three years after its deployment (2000-2002). Fish were sampled with a trammel net both at the rig and at an opensea control site placed at a distance of about 1.8 km, on the same type of seabed. At each survey, the catch obtained around the platform was subdivided based on the distance from the jacket (submerged part of the platform). Six strata, each 34 m wide, were identified up to 204 m horizontally from the rig. The platform showed its aggregation effect within the first year after installation. Catch rates significantly declined at increasing distances from the rig. The value recorded inside a 34 m radius from the structure was significantly higher than those obtained at distances greater than 140 m and at the control site. Reef-dwelling benthic fish, partially reef-dwelling pelagic and nekto-benthic species dominated inside the stratum closest to the rig, whilst the organisms which had no affinity towards hard substrates prevailed in the farther strata and at control site.