LONG-TERM TRENDS IN PELAGIC FISH STOCKS OF THE NORTH-SEA AND ADJACENT WATERS AND THEIR POSSIBLE CONNECTION TO HYDROGRAPHIC CHANGES

Some pelagic fish stocks in the North Sea and the waters west of Scotland have shown long-term trends in abundance and distribution that cannot be explained by changes in fishing effort. Examples are the recruitment failure of herring, both in the North Sea and to the west of Scotland in the 1970's, the North Sea sprat boom in the 1970's, and the changed distribution of adult and juvenile mackerel west of the British Isles. Results from the British Continuous Plankton Recorder programme indicate that long-term changes have occurred in the ecosystem of the North Sea and adjacent parts of the Atlantic. Most of the observed changes in fish stocks could be explained by a theory which assumes a long-term reduction in the flow of Atlantic water along the west coast of Scotland and into the North Sea during the period 1960-1980, and an increase of this flow in later years. However, there is as yet no physical oceanographic evidence that such a change indeed occurred. © 1990.