Intra and inter-annual patterns of juvenile Pacific salmon (Oncorhynchus) growth in the Strait of Georgia, British Columbia

Abstract

Early marine growth in juvenile salmon is positively correlated with overall survival to reproductive age. This study consists of two parts, in the first, regional patterns of juvenile coho (Oncorhynchus kisutch), Chinook (O. tshawytscha), chum (O. keta), pink (O. gorbusha), and sockeye (O. nerka) salmon early marine growth were analyzed over a three-year period (2012-2014) to provide insight into possible mechanisms regulating regional and inter-annual variation in survival. Insulin-like growth factor-1 (IGF1), a hormone used to assess instantaneous growth in fishes, was measured in late June and early July in the Strait of Georgia, Johnstone Strait, and Queen Charlotte Strait throughout the inside passage of British Columbia. All species showed significantly lower IGF1 concentration in both Johnstone and Queen Charlotte Strait when compared to the Northern Strait of Georgia (p<0.05). The second part of the study focused on coho and chum salmon in the Strait of Georgia. Coho salmon in 2012 and 2014 showed a strong similar pattern of IGF1 concentration and diet composition, with significantly lower IGF1 concentration in the south when compared to the north in each year (p<0.05). Coho salmon in 2013 showed less variation in IGF1 concentration and diet composition from north to south within the main basin of the Strait of Georgia. Overall, there was less regional variation in IGF1 concentration for chum salmon than coho salmon. However, chum salmon in Malaspina Strait had significantly higher IGF1 concentration in 2013 and 2014 when compared to the remainder of regions in the Strait of Georgia (p<0.05). There is a significant correlation between IGF1 concentration in coho salmon and the percent of herring in their diet among years (p<0.05). There were no correlations between sea-surface temperate, thermocline presence, or water column stability among years of high growth and years of low growth in the Strait of Georgia. These results show that there is significant regional variation in IGF1 concentration for juvenile salmon in the Strait of Georgia and surrounding waters.