Fluctuations of biomass of sardines (Sardina pilchardus, Walb.) in the Adriatic Sea

Sardine (Sardina pilchardus, Walb.) is - together with anchovy (Engraulis encrasicolus, L.) - a very important commercial fish species in the Mediterranean Sea, and, in particular, in the Adriatic Sea. The mean value of the annual catch of sardine in the Adriatic Sea is over 50.000 tons, in the time period 1975-1996. Since 1975, IRPEM is involved in research on sardine and anchovy abundance evaluation in the northern and central Adriatic Sea, by using population dynamic methods. In this paper, the biomass estimates obtained for the time interval 1975-1996 are discussed. These estimates were obtained using three different methods: Length Cohort Analysis (LCA), Virtual Population Analysis (VPA) and an "ad-hoc" modified version of the DeLury model with recruitment index. A comparison among the biomass estimates derived from these methods, based on different assumptions and data input, is made. Values as. well as patterns of biomass over time are consistent. In particular, strong fluctuations of biomass as a function of time are always evident.