Sardine and anchovy crises in northern Spain: natural variations or an effect of human activities?

Crises associated with the sardine and anchovy populations off northern Spain have been known and documented for centuries. From a review of the available historical and current literature relevant to this and other regions, it seems that most of the crises have been due to environmental factors, and only during the second half of the 20th century can the effects of fishing be viewed as having added to the recruitment failures observed in the populations of both species.