Marine growth patterns of southern British Columbia chum salmon explained by interactions between density-dependent competition and changing climate

• Published in: Canadian Journal of Fisheries and Aquatic Sciences
• Main Authors: Debertin, Allan J., Irvine, James R., Holt, Carrie A., Oka, Gladys, Trudel, Marc
• Format: Article in Journal/Newspaper
• Language: English
• Published: Canadian Journal of Fisheries and Aquatic Sciences 2017
• Subjects: Dunsmore; Hudson; Keta; Pacific; Sockeye; Oncorhynchus gorbuscha; Pink salmon
• Online Access: https://doi.org/10.1139/cjfas-2016-0265; https://dspace.library.uvic.ca//handle/1828/9969

Thirty-nine years of scale growth measurements from Big Qualicum River chum salmon (Oncorhynchus keta) in southern British Columbia demonstrated that competition and climate variation affect marine growth and age-at-maturity. A longitudinal study design that accounted for correlation among individuals revealed growth at all ages was reduced when the biomass of North American chum, sockeye (Oncorhynchus nerka), and pink salmon (Oncorhynchus gorbuscha) was high. When North Pacific Gyre Oscillation (NPGO) was positive, indicating increased primary productivity, predicted growth increased. Climate variation influenced competition effects. For instance, density-dependent competition effects increased when NPGO became more positive and Pacific Decadal Oscillation became more negative (indicating cool conditions), causing the greatest range in predicted scale size. Chum salmon are likely to exhibit continued reduction in growth at age due to increased ocean temperatures driven by climate change and high aggregate salmon biomass that includes hatchery releases. If evidence of biomass and climate effects presented here are common among Pacific salmon populations, reduction of hatchery releases should be considered. We appreciate the assistance of the many biologists and technicians who worked at Big Qualicum River Hatchery over the years. We acknowledge the contribution of members of the DFO Sclerochronology Lab: Shayne MacLellan for her support and Judy MacArthur and Mary Jane Hudson for remeasuring scales for quality control and assisting with some of the yearly scale measurements. We also recognize the assistance of Barbara Dunsmore, who provided biological data for Big Qualicum chum salmon, and Nora Crosby, who retrieved scales from the DFO archives. We thank Carl Schwarz for advice on statistical analyses, as well as Greg Ruggerone for his consultation on preliminary results. The first author thanks his Ph.D. supervisor, Tom Nudds, for the leave of absence to pursue this study and DFO's International Governance ...