Small pelagic fish biomass in relation to environmental parameters in the Adriatic Sea

Small pelagic fish biomass varies greatly in space and time. This phenomenon is very important in the ecological and economic contexts and reflects the effect of climatic changes both on macro and micro scale. The main difficulty in understanding the relationships between pelagic biomass fluctuations and the environmental parameters is the lack of synoptic biologic and climatic data over a long period of time. In this paper temporal fluctuations of anchovy biomass in Adriatic Sea are analysed jointly with the environmental parameters. Acoustic estimation of small pelagic fish biomass as a whole and per species has been conducted since 1976 in the Northern Adriatic Sea and since 1987 in the Southern Adriatic Sea. Sea surface temperature (SST) data were collected from NOAA satellite images since 1982. The results show that fluctuations of the total pelagic biomass have an almost regular periodicity, while biomass per species have more unpredictable variations; the famous collapse of anchovy stock occurred in the years 1986-90 seems related to a decrease of sea surface temperature. Furthermore in the last echo surveys environmental parameters were also measured in the water column by means of CTD probe; a trial analysis limited to 2005 has been conducted to try to identify the characteristics of the water masses that are mostly suitable for the presence of anchovy juveniles