The Food and Migration of the Perch (Perca fluviatilis) in Windermere

Abstract

THE results recorded in this paper were obtained while working at the Laboratory of the Freshwater Biological Association between July 1933 and February 1935. The perch (Percafluviatilis Linn.) is very abundant in Windermere and was suitable for an investigation, since it could easily be obtained in sufficient numbers to make observations on its food and migrations possible. Windermere is the largest of the English lakes, having a length of 10-5 miles (16-8 km.), and a mean breadth of about 950 yards (874 m.). It is a deep lake, the mean depth being about 78 ft. (c. 24 m.), and the littoral zone is usually narrow. In addition to the perch the following species of fish are also found in the lake: salmon (Salmo salar), brown trout (Salmo fario), char (Salvelinus willughbii), pike (Esox lucius), eel (Anguilla vulgaris), minnow (Phoxinus phoxinus), stickleback (Gasterosteus aculeatus), and bullhead (Cottus gobio). Of the larger species, the perch is by far the most common and occurs in the lake in very large numbers. Its average size is small, perch over 8 in. in length being uncommon and those over 12 in. in length very rare. The comparative scarcity of the larger fish is illustrated by Table 1, which shows the size distribution of the perch examined. Various methods were used for the capture of perch, and each of these tended to catch fish of a particular range of sizes. Consequently Table 1 does not represent accurately the actual size distribution of the perch in the lake, but it does illustrate the rapid decrease in numbers of perch more than 5-5 in. (14-0 cm.) long. The comparatively small number of perch less than 4 0 in. (10-2 cm.) in length which was examined is due to the fact that the trap in which most of the fish were caught allowed those less than 4-0 in. in length to escape.