title: Adaptive capacity at the northern front: sockeye salmon behaviourally thermoregulate during novel exposure to warm temperatures.
abstract: As climate change increases maximal water temperatures, behavioural thermoregulation may be crucial for the persistence of coldwater fishes, such as salmonids. Although myriad studies have documented behavioural thermoregulation in southern populations of salmonids, few if any have explored this phenomenon in northern populations, which are less likely to have an evolutionary history of heat stress, yet are predicted to experience substantial warming. Here, we treated a rare heat wave as a natural experiment to test whether wild sockeye salmon (Oncorhynchus nerka) at the northern extent of their primary range (60° latitude) can thermoregulate in response to abnormally high thermal conditions. We tagged adult sockeye salmon with temperature loggers as they staged in a lake epilimnion prior to spawning in small cold streams (n= 40 recovered loggers). As lake surface temperatures warmed to physiologically suboptimal levels (15-20°C), sockeye salmon thermoregulated by moving to tributary plumes or the lake metalimnion. A regression of fish body temperature against lake surface temperature indicated that fish moved to cooler waters when the epilimnion temperature exceeded ~12°C. A bioenergetics model suggested that the observed behaviour reduced daily metabolic costs by as much as ~50% during the warmest conditions (18-20°C). These results provide rare evidence of cool-seeking thermoregulation at the poleward extent of a species range, emphasizing the potential ubiquity of maximal temperature constraints and the functional significance of thermal heterogeneity for buffering poikilotherms from climate change.
authors.affiliation: Department of Fisheries and Wildlife , Oregon State University , 104 Nash Hall, 2820 SW Campus Way, Corvallis, OR 97331, USA.
authors.forename: Jonathan B
authors.initials: JB
authors.lastname: Armstrong
authors.affiliation: Northwest Fisheries Science Center, National Oceanic and Atmospheric Administration, 2725 Montlake Boulevard East, Seattle, WA 98112, USA.
authors.forename: Eric J
authors.initials: EJ
authors.lastname: Ward
authors.affiliation: School of Aquatic and Fishery Sciences , University of Washington , Box 355020, Seattle, WA 98105, USA.
authors.forename: Daniel E
authors.initials: DE
authors.lastname: Schindler
authors.affiliation: School of Aquatic and Fishery Sciences, University of Washington, Box 355020, Seattle, WA 98105,USA; Center for Limnology, University of Wisconsin, 680 North Park Street, Madison, WI 53706,USA.
authors.forename: Peter J
authors.initials: PJ
authors.lastname: Lisi
keywords: Climate change; latitude; refuge; thermal heterogeneity