Spatial and Interannual Variability of Juvenile Coho Salmon Growth in the Strait of Georgia (2012-2015)

We conducted a 4 yr (2012-2015) study of regional growth of juvenile coho salmonOncorhynchus kisutchin the Strait of Georgia (British Columbia, Canada). Size (fork length) and growth (insulin-like growth factor-1 [IGF-1] concentration) varied both regionally and inter-annually. Additionally, we found a positive relationship between IGF-1 concentration and fork length that varied between years, with slopes andy-intercepts higher in 2012 and 2014, respectively, as compared to 2013 and 2015. An ordinal increase of IGF-1 concentration from the south to north in 2012 and 2014 was coupled with an increase in the prevalence of both juvenile herring and juveniles of other fish species in the diet. Across all years, there was a positive relationship between regional mean IGF-1 concentration and regional mean percent of juvenile herring in the diet. Our study demonstrates relatively small-scale spatial heterogeneity in juvenile coho salmon growth that in part, was attributed to regional variation in diet. These findings also demonstrate the utility of short-term growth measures (such as IGF-1) for assessing relatively small-scale spatial and temporal differences in growth.