Variations in the distribution of blue whiting in the Barents Sea: climatic influences or year class effects?

Blue whiting (Micromesistius poutassou) in the Barents Sea represent the north-eastern fringe of the distribution of the species in the Atlantic. Distribution and abundance of blue whiting in the Barents Sea have fluctuated markedly over the past 20 years: in some years, the species appears to be very common and widespread, whereas in other years it is much more scarce and its range appears to become contracted. These variations have at least two potential explanations. First, increases in abundance may be related to variations in the influx or distribution of warm Atlantic water in the area. Second, rich year classes may temporarily expand the distribution area of blue whiting in the Barents Sea (either through direct density effects or climate-recruitment interactions). We investigate these explanations using data from scientific surveys conducted by the Institute of Marine Research during the period 1982-2002. Because of differences in survey coverage, we restrict the analysis to the south-western Barents Sea. Variations in abundance and distribution are correlated with both recruitment and oceanographic conditions. Regression analyses suggest that the variations in abundance are dominated by variations in year class strength, strong year classes leading to high abundance of blue whiting in the study area one or two years later. However, also salinity in the Fugløya-Bear Island –section during the previous year has a significant effect, suggesting that strong inflow of Atlantic water promotes high abundance of blue whiting. Warm years are associated with the centre of gravity of the distribution being more northern and western than during cold years