title: Is fishing selective for physiological and energetic characteristics in migratory adult sockeye salmon?
abstract: There is extensive evidence that fishing is often selective for specific phenotypic characteristics, and that selective harvest can thus result in genotypic change. To date, however, there are no studies that evaluate whether fishing is selective for certain physiological or energetic characteristics that may influence fish behaviour and thus vulnerability to capture. Here, adult sockeye salmon (Oncorhynchus nerka) were used as a model to test the null hypothesis that fishing is not selective for specific physiological or energetic traits. Fish were intercepted during their spawning migrations, implanted with a gastric radio transmitter, and biopsied (i.e., non-lethally sampled for blood, gill tissue and quantification of energetic status). In both 2003 and 2006, we tagged and biopsied 301 and 770 sockeye salmon, respectively, in the marine environment en route to their natal river system to spawn. In 2006 an additional 378 individuals were tagged and biopsied in freshwater. We found that 23 (7.6%) of the marine fish tagged in 2003, 78 (10.1%) of the marine fish tagged in 2006 and 57 (15.1%) of the freshwater fish tagged in 2006 were harvested by one of three fisheries sectors that operate in the coastal marine environment and the Fraser River (i.e. commercial, recreational or First Nations fisheries between the site of release and Hell's Gate in the Fraser River, approximately 250 km upriver and 465 km from the ocean tagging site). However, fisheries were not open continually or consistently in different locations and for different fisheries sectors necessitating a paired analytical approach. As such, for statistical analyses we paired individual fish that were harvested with another fish of the same genetic stock that was released on the same date and exhibited similar migration behaviour, except that they successfully evaded capture and reached natal spawning grounds. Using two-tailed Wilcoxon matched pairs signed-rank tests, we revealed that the physiological and energetic characteristics of harvested fish did not differ from those of the successful migrants despite evaluating a number of biochemical (e.g. plasma metabolites, cortisol, plasma ions, gill Na(+)/K(+)-ATPase) and energetic (e.g. gross somatic energy density) variables (P's all >0.10). However, for some analyses we suffered low statistical power and the study design had several shortcomings that could have made detection of differences difficult. We suggest that additional research explore the concept of fishing-induced selection for physiological characteristics because physiology is closely linked to three traits where fisheries-induced selection does occur (i.e. life-history, behaviour and morphology).
authors.affiliation: Fish Ecology and Conservation Physiology Laboratory, Ottawa-Carleton Institute of Biology and Institute of Environmental Science, Carleton University Ottawa, ON, Canada ; Centre for Applied Conservation Research, Department of Forest Sciences, University of British Columbia Vancouver, BC, Canada.
authors.forename: Steven J
authors.initials: SJ
authors.lastname: Cooke
authors.affiliation: Centre for Applied Conservation Research, Department of Forest Sciences, University of British Columbia Vancouver, BC, Canada.
authors.forename: Michael R
authors.initials: MR
authors.lastname: Donaldson
authors.affiliation: Centre for Applied Conservation Research, Department of Forest Sciences, University of British Columbia Vancouver, BC, Canada ; Institute for Resources, Environment and Sustainability, University of British Columbia Vancouver, BC, Canada.
authors.forename: Scott G
authors.initials: SG
authors.lastname: Hinch
authors.affiliation: Centre for Applied Conservation Research, Department of Forest Sciences, University of British Columbia Vancouver, BC, Canada.
authors.forename: Glenn T
authors.initials: GT
authors.lastname: Crossin
authors.affiliation: Fisheries and Oceans Canada, Science Branch, Pacific Region, Cooperative Resource Management Institute, School of Resource and Environmental Management, Simon Fraser University Burnaby, BC, Canada.
authors.forename: David A
authors.initials: DA
authors.lastname: Patterson
authors.affiliation: Fish Ecology and Conservation Physiology Laboratory, Ottawa-Carleton Institute of Biology and Institute of Environmental Science, Carleton University Ottawa, ON, Canada.
authors.forename: Kyle C
authors.initials: KC
authors.lastname: Hanson
authors.affiliation: LGL Limited Environmental Research Sydney, BC, Canada.
authors.forename: Karl K
authors.initials: KK
authors.lastname: English
authors.affiliation: Ecosystem Science & Management Program, University of Northern British Columbia Prince George, BC, Canada.
authors.forename: J Mark
authors.initials: JM
authors.lastname: Shrimpton
authors.affiliation: Faculty of Agricultural Sciences and Department of Zoology, University of British Columbia Vancouver, BC, Canada.
authors.forename: Anthony P
authors.initials: AP
authors.lastname: Farrell
keywords: biotelemetry; fishing; harvest; individual variation; phenotypic; selectivity