Aspects of oceanographic variability on Scottish fishing grounds
This thesis discusses the results of recent oceanographic research conducted in the north-western North Sea and at Rockall Bank. Oceanographic studies have been conducted intermittently in these areas since the beginning of the present century but little progress has been made in understanding those processes that might influence fish stocks. It is shown that one of the prime reasons for this lack of understanding was the unavailability, until comparatively recently, of tools to provide appropriate data over a wide range of time and space scales. Significant advances in physical oceanographic research have, however, been made since the early 1970s following the invention of the recording current meter in the mid-1960s. In the north-western North Sea the Fair Isle Current, which has only recently been identified following extensive current meter surveys, is shown to have an impact on the primary production of the north-western North Sea. In particular, inter-annual changes in its strength can markedly alter the phytoplankton species composition and the rate of primary production. As a result of this the primary production of the north-western North Sea is subjected to large inter-annual fluctuations. At Rockall Bank the interaction between the physical and biological environment is more direct since inter-annual fluctuations in the year-class strengths of its fish stocks are influenced by the extent to which water is confined to the Bank. Current measurements demonstrate that the mechanism for containment is a Taylor column trapped over the Bank, which produces a clockwise circulation on its flanks. This circulation, which is strongest near the bottom, fluctuates at various time scales from weeks, months to years. There is some evidence that, when the Taylor column collapses, the renewal of water over the Bank is initiated by the cascading of old water from the Bank.