A study of perch (Perca fluviatilis L.) and pike (Esox lucius L.) in Windermere from 1941 to 1982

Windermere is a lake in the English Lake District. Perch, Perca fluviatilis L., were heavily exploited in the 1940s, and since then they have been monitored each spring by trapping. Pike, Esox lucius L., have been gill netted each winter since 1944, removing each year about one third of the population over 55 cm in length. Perch are the main food of pike. Major changes have been observed in several population characteristics, including numbers, year-class strengths, and growth. These changes were not always similar in the north and south basins of the lake. Three periods, 1942 to 1959, 1960 to 1968, and 1969 to 1975, have been identified, with summer temperatures variable, cool, and warm respectively. Temperature, predation, and cannibalism are suggested as the most important factors and their relative importance has varied in the different periods. Fishing policy has remained almost constant since the late 1940s, and the changes haveoccurred as a result of natural events.