LONG-TERM FLUCTUATIONS IN COD AND POLLACK ALONG THE NORWEGIAN SKAGERRAK COAST

We tested whether the long-term fluctuations in abundance of O-group c od Gadus morhua and pollack Pollachius pollachius sampled from 1919 to 1994 at 38 stations along the Norwegian Skagerrak coast might be rela ted to the North Atlantic Oscillation (NAO). The short-and long-term f luctuations of both species exhibited different spatial structures and were probably of different origins. The former, which were previously shown to be related to biotic interactions, displayed significant hig hest similarities across the smallest scales (0 to 21 km). In contrast , the long-term fluctuations were similar at a larger scale (equal to or larger than the Norwegian Skagerrak coast) and were probably due to extrinsic factors. We have shown that the climatic conditions along t he Norwegian Skagerrak coast and the fluctuations of Calanus finmarchi cus in the Skagerrak were closely associated with the NAO. Long-term f luctuations of cod and pollack were, however, not associated linearly or non-linearly with the NAO or C. finmarchicus. Trends of cod and pol lack appeared to be related to the long-term fluctuations in the botto m sea grass coverage, mainly constituted by Zostera marina, and it can not be dismissed that fishing has contributed to the recent decline of these fish populations. We also conclude that the postsettlement peri od is crucial for these populations because of competition for space.