Influences of ocean conditions and feeding ecology on the survival of juvenile Chinook Salmon (Oncorhynchus tshawytscha)

Recruitment variability in many fish populations is postulated to be influenced by climatic and oceanographic variability. However, a mechanistic understanding of the influence of specific variables on recruitment is generally lacking. Feeding ecology is one possible mechanism that more directly links ocean conditions and recruitment. We test this mechanism using juvenile Chinook Salmon (Oncorhynchus tshawytscha) collected off the west coast of Vancouver Island, British Columbia, Canada, in 2000-2009. Stable isotopes of carbon (C-13), an indicator of temperature or primary productivity, and nitrogen (N-15), an indicator of trophic position, were taken from muscle tissues of genetically stock-identified salmon. We also collated large-scale climate indices (e.g., Pacific Decadal Oscillation, North Pacific Gyre Oscillation), local climate variables (e.g., sea surface temperature) and copepod community composition across these years. We used a Bayesian network to determine how ocean conditions influenced feeding ecology, and subsequent survival rates. We found that smolt survival of Chinook Salmon is predicted by their C-13 value, but not their N-15. In turn, large-scale climate variability determined the C-13 values of salmon, thus linking climate to survival through feeding ecology, likely through qualities propagated from the base of the food chain.