An assessment of biomass and diel activity of fish at an artificial reef (Adriatic Sea) using a stationary hydroacoustic technique

The biomass of fish assemblage inhabiting the Senigallia artificial reef (northern Adriatic Sea, Italy) was evaluated in the period July–November 1996. Density and biomass were assessed through a stationary hydroacoustic technique using an appropriately adapted SIMRAD EY500 system. Part of the system was placed inside the reef and it was linked by radio-modem to the Institute. Four ES120 split-beam acoustic transducers were used. The data gave useful information about the daily behaviour of the fish assemblage living at the reef: during the whole period the lowest densities were generally recorded in the early afternoon, whilst the highest abundances were commonly observed late in the night and early in the morning. It was confirmed that in late summer–early autumn, most of the reef fishes migrated from the coastal shallow waters to offshore. Throughout the study period fish abundance was higher inside the reef and decreased significantly at a distance of about 80 m. Moreover, the fish assemblage did not appear to be homogeneously distributed inside the reef. The highest values were recorded in the central part of the area where several structures of different shape were placed.