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UBC Theses and Dissertations

An investigation of a potential carrying capacity of coho and chinook salmon in the Georgia Strait Mountain, Scot Alexander


Stable or decreasing catches in conjunction with increasing hatchery releases have suggested decreasing marine survival rates for populations of Pacific salmon (Oncorhynchus sp.) in the Georgia Strait. I examined the possibility that a carrying capacity is imposing limits on the populations of coho (Onchorhynchus kisutch) and chinook (Oncorhynchus tshawytschd) salmon. Two investigations were carried out; the first involved an examination of the impact that juvenile salmon have on their food supply. The second used a computer model to predict the possible results that a hatchery based fisheries manipulation might produce under different experimental protocols. The feeding study suggested that juvenile salmon might be having, a much greater impact on their available food supply than has previously been suspected. Overall, it was estimated that chinook and coho together consume an average of 4% to 6% of their main foods daily. If these impacts are taken together with those of other species, this suggests that a carrying capacity might well be important. A hatchery manipulation experiment is one obvious way to test for a marine survival limit as implied by a carrying capacity. Using a metagaming approach to model such an experiment, insights were obtained into how it could be performed most efficiently. The results suggest that, depending on the required outcome, it would be advisable to maintain current exploitation rates of both coho and chinook stocks during such an experiment. Other factors that would favor a rapid conclusion to the experiment are extreme as opposed to conservative manipulations, and minimal attempts to rebuild stocks through other means. However, even if these recommendations are heeded, the model suggests that a hatchery experiment might need to be a long term project. With reductions in hatchery releases as high as 75% every second year, average times to produce conclusive results were on the order of a decade or more.

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