Oceanographic Influences on the Feeding Ecology of Juvenile Chinook Salmon

Recruitment variability in many fish populations is postulated to be influenced by climactic and oceanographic variability. However, a mechanistic understanding of how specific variables can ultimately influence recruitment is lacking. As fish may experience size-selective mortality during critical life stages, feeding ecology is one possible mechanism that links oceanography and recruitment directly through growth rates. We test this mechanism using juvenile Chinook Salmon off the West Coast of Vancouver Island in 2000-2009. Stable isotopes of carbon (δ¹³C), an indicator of primary productivity or temperature, and nitrogen (δ¹⁵N), an indicator of trophic position, were taken from muscle tissues of genetically stock-identified salmon. We also collected large-scale climate indices (e.g Pacific Decadal Oscillation, North Pacific Gyre Oscillation), local climate variables (e.g sea surface temperature, salinity), and zooplankton community composition for all years. We used a Bayesian Network to determine how these variables influenced feeding ecology, and subsequent survival rates. We found that the survival rate of juvenile Chinook Salmon is predicted by their δ¹³C value, but not their δ¹⁵N. In turn, both large-scale and local climate variables determined the δ¹³C values of salmon, thus linking climate to survival through feeding ecology, likely through qualities propagated from the base of the food chain.