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Aquatic Biology

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AB 5:281-292 (2009)  -  DOI:

Differences in the trophic role of Mysis diluviana in two intermontane lakes

John D. Whall1, David C. Lasenby2,*

1Watershed Ecosystems Program, and 2Department of Biology, Trent University, 1600 West Bank Drive, Peterborough, Ontario K9J 7B8, Canada
*Corresponding author. Email:

ABSTRACT: The trophic role of the freshwater shrimp Mysis diluviana was compared between 2 neighbouring lakes in British Columbia to investigate its possible role in the collapse of the Okanagan Lake kokanee salmon Oncorhynchus nerka population. Stable isotopes of nitrogen (δ15N) and carbon (δ13C) were used to compare the trophic relationships of mysids within the pelagic food web and between lakes. Mid-summer δ15N signatures suggested that adult mysids in Okanagan Lake were acting more as primary consumers, and Kalamalka Lake mysids were acting as secondary consumers. M. diluviana’s predatory capacity was also assessed through in situ clearance rate feeding experiments and examination of gut contents. M. diluviana <1 yr old in Okanagan Lake were capable of clearing a greater volume of prey, but there was no difference between lakes for M. diluviana >1 yr old. Gut contents confirmed M. diluviana in both lakes were consuming copepod and cladoceran prey. All 3 techniques demonstrated ontogenetic diet shifts, with larger mysids obtaining more energy from zooplankton prey. Although mysids in feeding experiments actively consumed the same zooplankton prey as kokanee, δ15N and δ13C ratios suggest that mysids in Okanagan Lake were not feeding at the same trophic level as kokanee, which indicates that there may have been less competition for food sources than previously thought. These differences in results suggest that predatory capacity, as indicated by in situ feeding experiments or gut content analysis, should not be used in isolation to establish trophic roles for omnivorous animals.

KEY WORDS: Mysis relicta · Mysis diluviana · Stable isotopes · Trophic position · Okanagan Lake · Clearance rates

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Cite this article as: Whall JD, Lasenby DC, (2009) Differences in the trophic role of Mysis diluviana in two intermontane lakes. Aquat Biol 5:281-292.

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