Fluctuation in stock properties of north-east Arctic cod related to long-term environmental changes

From a historic perspective, the north-east Arctic cod stock, which is found in the Barents Sea-Svalbard region, has been the most productive gadoid stock in the Atlantic. Variation in catch has always been large, but during the last 10-15 years catch and stock abundance have reached the lowest level on record. Three major causes of variation have been discussed: (i) stock reduction through exploitation; (ii) environmental influences on recruitment; and (iii) species interaction effects on maturation, growth and mortality. In addition, interactions among these three sources might be important. The influence of each specific factor is difficult to evaluate from incidental observations and short-term time series. In this respect, the time series on catches and on biological and environmental information of this stock, which partly extend back to the 19th century. occupy a unique position in comparison to data on most other stocks. In this paper, fluctuations in catch and stock abundance are compared with changes in recruitment, size/age and growth. This information is discussed in view of historic variation in ecology and environment. The stock has been under particularly high exploitation pressure since the mid-1970s. Further, large changes in growth rates and poor recruitment to the commercially exploited stock are characteristic of late 1980s and throughout the 1990s. The analysis shows that substantial long-term variation might underlie short-term variability, and more importantly, that long-term changes roughly coincide with similar fluctuations in the environment. Such factors might substantially affect the relationship between spawning stock and recruitment, which is also apparent from the difference in conclusions reached by various published studies. Consequently, it is suggested that using a steady-state perspective for the population dynamics may lead to mismanagement and to a reduction of the long-term yield from this stock.