How Does Fish Behavior Change during the Day around Gas Platforms?

It is well known that offshore gas and oil extraction platforms act as artificial reefs that create a haven for finfish species. Being attracted to hard substrates, fish schools usually aggregate around the jackets or legs of the platforms where they are afforded some protection from predators and benefit from high concentrations of prey and smaller organisms foraging in the area. However, even though higher fish densities are reported near the structures, behavior and movements of fish schools around the platforms have not yet been properly investigated. In such context, this chapter investigates the diurnal spatial movements of schooling fish around three gas extraction platforms placed in the north-central Adriatic Sea to improve knowledge on how these structures influence the surrounding fish assemblage. Hydroacoustic multibeam echosounder surveys were conducted for 1 year at dawn, noon, and dusk. Results highlighted the variation in fish biomass around the platforms related to the time of the day and distance from the structure. Recognizing a constant attraction of fish to the platforms during daylight hours (i.e., dawn to dusk), fish biomass was greater near the gas platforms, especially at dusk. Oppositely, variation in the morphometric features of fish schools occurred during the daytime only for the school volume associated with platforms at deeper depths. Complementary information on the fish assemblages associated with the gas platforms derived from fishing surveys allowed a better understanding of the diurnal behavior of fish schools around the structures.