Effects of environmental variables on recruitment of anchovy in the Adriatic Sea

The anchovy Engraulis encrasicolus is an important fishery resource in the Adriatic Sea. Fluctuating recruitment of young fish to the stock over time can be related to changes in the environment. The trend of anchovy recruitment in the northern and central Adriatic from 1975 to 2001 was analysed with the aim of identifying possible effects related to 5 environmental factors: surface air temperature, surface atmospheric pressure, quadrant specific wind stresses, Po River runoff and North Atlantic Oscillation (NAO) index. Particular emphasis was placed on 1987, a year of anchovy collapse and fishery crisis. Different types of regression models were applied, both linear and nonlinear (simple and multiple), with predictor variables being environmental factors and parental stock abundance. Positive relationships of number of recruits with autumnal SSE and ESE wind stress and both annual and autumnal Po River runoff were found, with a strength comparable to the relationship between recruits and parental stock. Low levels of these environmental factors were observed just before the 1987 collapse, together with a high frequency of occurrence of NE winds and an extreme positive value of the NAO index in the previous autumn (which may have been unfavourable to recruitment in 1987). All 5 environmental factors could be related to increased or reduced food availability for young stages of anchovy in autumn.