Creel and lake survey data from 87 Ontario lakes with self-sustaining lake trout (Salvelinus namaycush) populations were analysed to determine the effect of intrinsic factors, such as fish community structure, and extrinsic factors, such as angling-effort, on the observed yields of lake trout. Multiple regression analyses showed that angling-effort and lake area, in order of importance, explained almost 82% of the variation in annual catches. Analyses of covariance were used to test a variety of hypotheses about how community structure — the presence of forage, competitors, or alternate sports species — affected the catch of lake trout. No significant differences among groups were detected, which suggests that fish community structure has little or no effect on actual yield of lake trout. The difficulties inherent in using catch and effort data alone to evaluate the importance of factors affecting productivity (or potential yield) are discussed.
The methodology of studying changes in the Gobi region`s lake area
