| Population declines and extirpations have occurred for bull trout ( Salvelinus confluentus) throughout their range in western North America. Causes for these declines or extirpations include overexploitation, competition with non-native fishes, habitat destruction and habitat fragmentation. The management and conservation of this species requires that we understand the fundamental mechanisms regulating their populations. However, the environment and biology of these fish sets them apart from many other fishes for which mechanisms of population regulation have been developed. Juvenile bull trout can spend several years rearing in small unproductive streams where they may compete with conspecifics for resources that are limiting. Observations and experiments described in this thesis show that competition does occur for some limited resource and is exploitative in nature. Exploitative competition across age cohorts can result in cyclic population dynamics, which contrasts stable dynamics which result from similar interactions confined to a single cohort. The analysis of a physiologically structured population model developed for bull trout suggest that population cycles may arise from two different mechanisms, variability in overwinter survival or variability in age- and size-at-maturity. Empirical data for bull trout support the assumptions of the model and presence of population cycles. However, given the predicted period of these cycles (>6–7 years), it is difficult to conclusively determine a cyclic pattern in the empirical data which was collected over a relatively short time frame (≤15 years).; At a regional scale, the distribution of bull trout in stream reaches from the eastern slopes of the Canadian Rocky Mountains (Kananaskis Country, Alberta) was inversely related to non-native brook trout (S. fontinalis ). Bull trout were more likely to be present in higher elevation reaches and the converse was true for brook trout. The presence of brook trout at lower elevations could not be explained from their past stocking history, but rather, represented downstream movements and colonization of these reaches. The mechanism responsible for downstream colonization by brook trout is not known. However, the sensitivity of bull trout, compared with brook trout, to overexploitation by anglers may have been a factor in shaping the observed distribution. |
