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UBC Theses and Dissertations

Population dynamics and interactions of sockeye and kokanee salmon (Oncorhynchus nerka) with piscivorous char (Salvelinus sp.) and rainbow trout (O. mykiss) in the large lakes and reservoirs of British Columbia Woodruff, Patricia Elizabeth


Freshwater fisheries management is focused on a combination of economic, social and conservation objectives. One of the trade-offs among these objectives involves a balance between harvest and consistent ecosystem functions. There can be conflicts between recreational fisheries and conservation, which are exacerbated by other habitat uses, such as dam operations. This dissertation examines the tools used by managers; how strategies employed by managers interact with natural systems and each other; what are some of the unexpected consequences; and what impact these tools have on recreational freshwater fisheries objectives. First, the use of nutrient addition as a tool to increase fish production is examined. Ecosystem modelling is then used to look at the impact of nutrient addition on target fish species in combination with different flow regimes in a highly managed reservoir. A decision analysis table is used to compare effects of different nutrient addition scenarios under variable flow conditions. Nutrient addition was found to be the most important driver of the system, with constant nutrient addition resulting in higher biomasses of the target fish species. Next, the outcomes of different stocking programs in British Columbia are summarized. The potential effect of salmon reintroduction programs on native fish species was predicted using ecosystem modelling. These models indicated that higher stocking levels had negative effects on the native kokanee salmon, but resulted in variable effects on the predators, depending on the species being stocked. Finally, ecosystem modelling is used to look at the possible effects of invasive non-native mussels in a productive lake. The model predicted that fish species that remained in the lake would be affected the most, while the invasive mussels had less of an effect on anadromous sockeye salmon and rainbow trout that reared in streams. This dissertation shows that maintaining consistent ecosystem functions to support recreational fisheries objectives can be challenge in itself.

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