MARINE TEMPERATURES EXPERIENCED BY POSTSMOLTS AND THE SURVIVAL OF ATLANTIC SALMON, SALMO-SALAR L., IN THE NORTH-SEA AREA

The survival of two Atlantic salmon stocks that inhabit rivers conflue nt with the North Sea was examined in respect to historical distributi ons of sea surface water temperatures. The rivers Figgjo and North Esk are relatively small salmon rivers in southern Norway and eastern Sco tland, respectively. Wild salmon smelts have been tagged in these rive rs since 1965. Tag returns were used to evaluate the survival of salmo n in the North Sea. Survival rates of one-sea-winter (1SW) and 2SW fis h were correlated within stocks, as well as between stocks, Survival r ates were compared with the areal extent of thermal habitat in the nor th-eastern Atlantic Ocean. A positive correlation was found between th e area of 8-10 degrees C water in May and the survival of salmon. A re ciprocal negative correlation was also found between survival and 5-7 degrees C water in the same month. An analysis of sea surface temperat ure distributions for periods of good vs. poor salmon survival showed that when cool surface waters dominate the Norwegian coast and North S ea during May, salmon survival has been poor. Conversely, when the 8 d egrees C isotherm has extended northward along the Norwegian coast dur ing May, survival has been good. The effect of water temperature distr ibutions on the growth of postsmolts and other survival factors are di scussed.