Dynamics of Unexploited and Lightly Exploited Populations of Rainbow Trout (Salmo gairdneri) from Coastal, Montane, and Subalpine Lakes in Western Canada

Populations of rainbow trout (Salmo gairdneri) in one coastal and two montane lakes were characterized by a relatively stable age structure, approximately 50% annual mortality, maximum longevity of 7 yr, and close to linear growth beginning at age 1 or age 2. In contrast, populations in subalpine lakes were characterized by an unstable age structure, large annual variation in recruitment, maximum longevity of 13 yr or more, and growth patterns that were either asymptotic, complex, or linear. Age structure and thus year-class strength was directly related to cumulative summer temperature in one subalpine lake (r = 0.71, N = 11), and in others, strong year-classes were often associated with warm summers. These analyses indicate that the magnitude of recruitment in subalpine lakes was either primarily or at least partly due to annual differences in summer temperature. Longevity was inversely related to midsummer water temperature.