MANAGEMENT IMPLICATIONS FOR A LACUSTRINE BROOK TROUT POPULATION: AN INVESTIGATION IN AGE PRECISION AND POPULATION DYNAMICS

Abstract

Areas in the Columbia River Basin have been impacted by hydroelectric dam developments, requiring some anadromous and resident fish losses to be mitigated with resident fisheries enhancement. Brook Trout are one resident fish species being selectively managed by the Confederated Tribes of the Colville Reservation to mitigate for these losses and contribute to desirable subsistence and recreational fisheries. The Owhi Lake Brook Trout fishery is particularly important as a tribal member only fishing lake, and fisheries managers are interested in investigating population dynamics to inform present management decisions. My dissertation investigates possible alternatives to ageing Brook Trout, supply-demand comparisons to inform potential food limitations, and models population viability in response to variable stocking programs. Scale and fin rays were found not to match otolith age, though age estimation was influenced by reader’s experience. Fin rays matched otolith age more than scales, but variability in age estimates was still greater than 5% CV. Prior experience ageing specific structures was the main factor influencing age estimates, given more agreement was found between readers with similar experience. Supply-demand comparisons identified 2017 as a period where Brook Trout demand exceeded littoral prey production. During this period, Brook Trout switched from preying primarily on littoral prey to pelagic zooplankton, ultimately increasing proportion of maximum consumption rates and lowering growth potential. Taken together, it is likely that the system’s capacity was exceeded in 2017. Matrix models suggest that the population’s growth rate was highest when Owhi Lake was not stocked. All models predict similar population sizes after 20 years, and each model’s population growth rate were not significantly different. Results suggest that Owhi Lake Brook Trout can likely be self-sustaining.