“Fish stocks and recruitment”: the past thirty years

Abstract

The last ICES Symposium on recruitment variability was held in Århus, Denmark, in the summer of 1970. The 1970 symposium brought together many important ideas on the topic. A contemporary perspective on recruitment variability is developed based on (1) the post-1970 accumulated record and (2) many of the ideas tabled in 1970. A brief review focuses on the multidecadal nature of recruitment variability and the fact that recruitment and its integral, stock size, often vary quite independently from fishing mortality, providing a strong implication that multidecadal changes in the environment are a major cause of recruitment variability. This evokes the old issue of the need to separate the effects of fishing from the effects of the environment. An important pathway leading to such a separation was suggested at the 1970 symposium. This pathway involved the notion that an understanding of recruitment variability required examining non-linear interactions among fish life-history stages. However, an intellectual tension between the need to examine life-history stages and the need to study factors affecting the mortality of fish larvae became apparent. These two approaches are now brought together by linking survival at the egg and early larval stage with fecundity. This generates a recruitment–stock curve that exhibits a collapsed and a non-collapsed phase and couples directly, in principle, with the physical structure of the environment.