PERCH IN BRITISH LAKES: A NEW FISHING INDUSTRY

Abstract

IT is common knowledge that progressive changes in the physical conditions of an environment are paralleled by changes in the plant and animal communities inhabiting it. One of the first workers to elaborate the principle for the freshwater environment was Pearsall¹, who illustrated it with reference to the plant communities of the English lakes, but recognized that the animal communities were subject to corresponding changes. Thus, in the fish fauna of the English lakes there is a tendency for the original association of species, dominated by char (Salvelinus willughbii) and brown trout, to change into one dominated by perch and pike. Under natural conditions the change is very slow, being connected with the accumulation of silt and the general increase in productivity of water resulting therefrom; but in certain cases unconscious intervention from man appears to have accelerated the process. Thus for Windermere there is some documentary and much hearsay evidence that during the past fifty years the char and trout, which formerly gave rise to prosperous food and sporting fisheries, have been largely superseded by perch and pike, the change having probably been hastened by a general increase of productivity resulting from the addition of sewage.