Spatiotemporal dynamics of food availability for juvenile coho salmon (Oncorhynchus kisutch) across a watershed habitat mosaic

Variation in food availability can influence fish growth, survival, and life history diversity. Yet, relatively few studies have investigated spatiotemporal variation in food availability among fish-bearing habitats at the watershed scale. In this study, we described spatial and seasonal patterns of food availability (invertebrate prey abundance, quality, and accessibility) for juvenile coho salmon (Oncorhynchus kisutch) in natal tributary streams and non-natal floodplain wetlands in the North Thompson watershed (British Columbia, Canada). We found striking seasonal differences between streams and wetlands for all dimensions of food availability. Notably, wetlands had up to 136 times greater prey abundance than streams throughout the rearing period. However, high prey abundance often coincided with high water temperature and low dissolved oxygen concentration that potentially limit prey accessibility in wetlands, suggesting that wetlands may be high-risk high-reward habitats. Comparatively low prey abundance in streams may be offset by more favourable abiotic conditions and higher-quality prey. Collectively, these results indicate that asynchrony in food availability generates a seasonally shifting portfolio of growth opportunities for juvenile salmon across a watershed habitat mosaic.