Year to year variation in the year-class strength of Perca fluviatilis

Summary

Fluctuations in the strength of the year-classes of perch in Windermere from 1940 to 1952 are described. These variations are mainly due to differences in the survival of the young fish and only slightly to variations in the number of eggs laid. Similar and synchronous fluctuations occur in other differing lakes in the same region. Possible causes are discussed and it is suggested that indirect climatic factors working through the food supply of the fry may be important.