Behavioral Ecology Advance Access originally published online on March 6, 2008
Behavioral Ecology 2008 19(4):747-758; doi:10.1093/beheco/arn006
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Physiological correlates of coastal arrival and river entry timing in late summer Fraser River sockeye salmon (Oncorhynchus nerka)
a Fish Ecology and Conservation Physiology Laboratory, Department of Biology and Institute of Environmental Science, Carleton University, 1125 Colonel By Drive, Ottawa, Ontario, K1S 5B6, Canada b Centre for Applied Conservation Research, Department of Forest Sciences, University of British Columbia, 2424 Main Mall, Vancouver, British Columbia, V6T 1Z4, Canada c Fisheries and Oceans Canada, Science Branch, Pacific Region, Cooperative Resource Management Institute, School of Resource and Environmental Management, Simon Fraser University, Burnaby, British Columbia, V5A 1S6, Canada d LGL Limited Environmental Research Ltd., 9768 Second Street, Sidney, British Columbia, V8L 3Y8, Canada e Institute for Resources, Environment and Sustainability, University of British Columbia, Vancouver, British Columbia, V6T 1Z4, Canada f Department of Biology, University of Northern British Columbia, Prince George, British Columbia, V2N 4Z9, Canada g Department of Integrative Biology, University of Guelph, Guelph, Ontario, N1G 2W1, Canada h Faculty of Agricultural Sciences and Department of Zoology, University of British Columbia, Vancouver, British Columbia, V6T 1Z4, Canada
Address correspondence to S.J. Cooke. E-mail: Steven_Cooke{at}carleton.ca.
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Abstract |
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Animal migrations typically occur within a predictable time frame and sequence, but little is known about the triggers that initiate migration, despite their importance in animal ecology and for resource management. The migration of adult sockeye salmon (Oncorhynchus nerka) in the Fraser River, British Columbia, Canada, is an excellent model to study such triggers because for nearly a decade a segment of the late summer stocks has been proceeding into the river as much as 6 weeks earlier than the historic norm. In this study, late-run sockeye salmon (N = 146) were intercepted about 215 km from the mouth of the Fraser River and implanted with radio transmitters. These fish were biopsied, which included drawing blood from the caudal vessels, removing some gill filament tips, and quantifying energetic status using a microwave energy meter. Fish that entered the river without delaying in the estuary were in a more advanced state of reproductive maturation, as evidenced by hormone and energy levels. Indicators of osmoregulatory preparedness (i.e., plasma ions and gill Na+/K+-ATPase activity) provided little insight into migration timing aside from greater variation in Na+/K+-ATPase activity in fish that entered early relative to those that held in the ocean. Given the dissimilar reproductive hormone profiles for early arrival into the estuary and early entry into the Fraser River, it appears that only a subset of the population are early migrants and triggers for early migration may be related to a relatively advanced reproductive development and higher energetic status. These findings provide the first assessment of the physiological correlates of migration timing and provide a mechanistic understanding of the proximate factors associated with abnormal migration timing in late-run sockeye salmon.
Key words: cues, energetics, migration behavior, timing.
Received 7 March 2005; revised 15 August 2007; accepted 15 January 2008.