Influence of temperature variability on recruitment of cod in the Barents Sea

Abstract

During the past fifteen years several studies have examined the influence of temperature variability on the recruitment of Arcto-Norwegian cod (Gadus morhua). The overall conclusion has been that year classes of high abundance occurred mainly during years with high temperature, while poor year classes occurred mainly during cold years. The present article quantifies the difference between year classes produced in warm and cold years. Separate calculations based on two different abundance indices from the international 0-Group Surveys in the Barents Sea for the years 1965 (1966) to 1992 show that the average production of Arcto-Norwegian cod larvae in warm years was about three times higher than in cold years. Similar calculations were done for haddock and for both species based on the virtual population analysis at age 3. The difference in both 0-group and virtual population analysis recruitment strength between warmer and colder years is statistically significant for cod and haddock for the 1965 to 1992 period. Our results show that the influence of temperature on cod recruitment has been stronger in the last 25 years than in the previous decades. In our opinion this added sensibility to environmental fluctuations is connected with the decline in size of the spawning stock and the change in its age composition