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UBC Theses and Dissertations

Competitive interactions between juvenile sockeye salmon (Oncorhynchus nerka) and limnetic zone sticklebacks (Gasterosteus aculeatus) O'Neill, Sandra M.


Evidence supporting the hypothesis that competitive interactions occur between juvenile sockeye salmon and limnetic sticklebacks in an oligotrophic lake was obtained by manipulating fish abundance, size and species combinations in limnetic zone enclosures in Kennedy Lake, British Columbia. Sockeye and sticklebacks were stocked at densities within the range known to commonly occur in British Columbia coastal lakes. In all fish-treatment enclosures, fish grazing pressure quickly reduced the abundance of large zooplankters and then maintained zooplankton communities containing primarily nauplii and rotifers, prey seldom consumed by fish. Mean size and abundance of zooplankton within a fishless control enclosure remained at significantly higher levels than those in Kennedy Lake or in test enclosures. Diets of fish sampled from enclosures at the end of feeding trials demonstrated that sockeye feeding by themselves (allopatric sockeye) consumed larger food items than sockeye feeding with sticklebacks (sympatric sockeye), whereas sympatric sticklebacks consumed larger food items than allopatric sticklebacks. I conclude that in many oligotrophic coastal lakes, where food supplies are limited, sockeye and sticklebacks may compete by exploiting the zooplankton communities to their mutual disadvantage. Further, competitive interactions between sockeye and sticklebacks result in dietary niche shifts by sockeye in allopatry vs. sympatry. Niche shifts by sticklebacks may involve both inter- and intraspecific competitive interactions.

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