Changes in body size of Canadian Pacific salmon over six decades

• Published in: Canadian Journal of Fisheries and Aquatic Sciences
• Main Authors: Jeffrey, Kyla M., Côté, Isabelle M., Irvine, James R., Reynolds, John D.
• Format: Article in Journal/Newspaper
• Language: English
• Published: Canadian Science Publishing 2017
• Subjects: Keta; Pacific; Sockeye; Oncorhynchus gorbuscha
• Online Access: http://dx.doi.org/10.1139/cjfas-2015-0600; http://www.nrcresearchpress.com/doi/full-xml/10.1139/cjfas-2015-0600; http://www.nrcresearchpress.com/doi/pdf/10.1139/cjfas-2015-0600

Body size can sometimes change rapidly as an evolutionary response to selection or as a phenotypic response to changes in environmental conditions. Here, we revisit a classic case of rapid change in body size of five species of Pacific salmon (Oncorhynchus spp.) caught in Canadian waters, with a six-decade analysis (1951–2012). Declines in size at maturity of up to 3 kg in Chinook (Oncorhynchus tshawytscha) and 1 kg in coho salmon (Oncorhynchus kisutch) during the 1950s and 1960s were later reversed to match or exceed earlier sizes. In contrast, there has been little change in sockeye salmon (Oncorhynchus nerka) sizes and initial declines in pink (Oncorhynchus gorbuscha) and chum salmon (Oncorhynchus keta) sizes have halted. Biomass of competing salmon species contributed to changes in size of all five species, and ocean conditions, as reflected by the North Pacific Gyre Oscillation and the Multivariate ENSO (El Niño – Southern Oscillation) indices, explained variation in four of the species. While we have identified a role of climate and density dependence in driving salmon body size, any additional influence of fisheries remains unclear.