Regional Patterns of Juvenile Salmon Growth in the Strait of Georgia and Surrounding Waters

Insulin-like growth factor-1 (IGF1) is a hormone used to assess instantaneous growth in fishes. IGF1 was measured in late June and early July from juvenile coho (Oncorhynchus kisutch) and chum (O. keta) salmon in the Strait of Georgia, Johnstone Strait, and Queen Charlotte Strait within the inland coast of British Columbia (2012 – 2014). A consistent pattern of significantly lower IGF1 was observed in coho in Queen Charlotte Strait, Johnstone Strait, Malaspina Strait, and the Gulf Islands across all years when compared to the main basin of the Strait of Georgia. Additionally, IGF1 of coho in even years (2012 and 2014) was significantly higher in the Discovery Islands, Desolation Sound, and Northern Strait of Georgia. Coho in the odd year (2013) showed less variation from north to south within the main basin. Overall, there was less regional variation in IGF1 for chum than coho. However, chum in Johnstone Strait and Queen Charlotte Strait generally had lower IGF1 (all years) and chum salmon in Malaspina Strait had significantly higher IGF1 in 2013 and 2014. These results show significant regional and inter-annual variation in IGF1 within each species and some regional variation that is similar across species.