MEPS 496:109-124 (2014)  -  DOI:

Theme Section: Tracking fitness in marine vertebrates

Variable thermal experience and diel thermal patterns of homing sockeye salmon in coastal marine waters

S. M. Drenner1,*, S. G. Hinch1, E. G. Martins2, D. Robichaud3, T. D. Clark4, L. A. Thompson5, D. A. Patterson5, S. J. Cooke2, R. E. Thomson6,**

1Department of Forest and Conservation Sciences, University of British Columbia, Vancouver, British Columbia V6T 1Z4, Canada
2Fish Ecology and Conservation Physiology Laboratory, Institute of Environmental Science and Department of Biology, Carleton University, Ottawa, Ontario K1S 5B6, Canada
3LGL Limited, 9768 Second Street, Sidney, British Columbia V8L 3Y8, Canada
4Australian Institute of Marine Science, PMB 3, Townsville MC, Queensland 4810, Australia
5Fisheries and Oceans Canada, Cooperative Resource Management Institute, School of Resource and Environmental Management, Simon Fraser University, Burnaby, British Columbia V5A 1S6, Canada
6Fisheries and Oceans Canada, Canada Institute of Ocean Science, PO Box 6000, Sidney, British Columbia V8L 4B2, Canada
*Corresponding author:

ABSTRACT: Temperature is recognized as a key factor influencing physiology, behaviour and survival of anadromous salmonids, yet little is known about their thermal experience, nor factors affecting it, during marine homeward migrations. In 2006 and 2010, approximately 1000 Fraser River sockeye salmon Oncorhynchus nerka were captured and tagged in coastal marine waters, ~215 km from the river mouth, during their spawning migration. Individual salmon were blood sampled, gastrically implanted with temperature loggers fixed to radio or acoustic tags, and released. We recovered 50 loggers from freshwater locales containing 14690 hourly temperature readings. Mixed-effects models were used to characterize marine thermal experience, and examine the association of thermal experience with initial physiological status as well as oceanographic and meteorological conditions. Sockeye salmon thermal experience was highly variable (8.4°C to 20.5°C), and we detected opposite diel patterns between study years that could be associated with moon phase, behavioural thermoregulation, olfactory/celestial navigation or predator avoidance. We were unable to find any relationships between thermal experience and environmental conditions or fish physiological state. Nonetheless, we found that the greatest variability in thermal experience was attributed to within-individual variation, suggesting that environmental and physiological variables need to be examined at different temporal and spatial scales, and/or additional environmental and physiological variables need to be assessed. Overall, the factors associated with the thermal experience of homing sockeye salmon in coastal marine environments are more complex than previously thought, and multiple year studies are needed before generalizing behavioural patterns observed from single year studies.

KEY WORDS: Temperature · Sockeye salmon · Migration · Behaviour · Physiology · Oceanography · Thermal logger · Telemetry

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**Amended author list. See Corrigendum
Cite this article as: Drenner SM, Hinch SG, Martins EG, Robichaud D and others (2014) Variable thermal experience and diel thermal patterns of homing sockeye salmon in coastal marine waters. Mar Ecol Prog Ser 496:109-124.

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