Fluctuation of sardine and anchovy abundance in the Strait of Sicily investigated by acoustic surveys

This study assembles the main results of the research carried out during the last several years on the application of hydro-acoustic technology to the evaluation of biomass and distribution of small-pelagic-fish species off the southern coast of Sicily. The biomass estimates and the population-density charts presented concern the two main species: sardine (Sardina pilchardus) and anchovy (Engraulis encrasicolus). Six acoustic surveys were carried out from 1998: in June 1998, October 1999, July and September 2000, October 2001 and July 2002. For biomass-evaluation purposes and for the study of distribution, hydro-acoustic data acquired at 38 kHz were used. Large inter-annual fluctuations were observed both for sardine and anchovy populations: sardine biomass estimates ranged from 6,000 metric tons in July 2002 to over 36,000 metric tons in July 2000; anchovy evaluations ranged from about 7,000 metric tons in June 1998 to 23,000 metric tons in October 2001. Such fluctuations suggest the importance of yearly recruitment success, which is affected by environmental variation. Acoustic estimates are largely consistent with the landings recorded in Sciacca (the main fishing port on the southern coast of Sicily for small-pelagic-fish species) during the year following the evaluation surveys, emphasizing their relevance not only to monitoring but also to managing such resources.