Linkages Between Salmon Survival, Their Timing of Sea Entry and Marine Productivity

Marine survival of coho and sockeye salmon have declined in the last 20 years potentially as a result of a mismatch between the smolts and their prey. Changes in the phenology of outmigration timing were assessed using long time series of coho and sockeye salmon smolts from the Strait of Georgia and the West Coast of Vancouver Island, British Columbia.

The overall trend and the annual variations (associated with early spring temperature) in outmigration timing was assessed using autoregressive model. Our results for coho suggests that timing is negatively related to year and early spring temperature,  i.e. migrating earlier in the spring through the years, and even earlier in years of warm spring conditions. In contrast, sockeye salmon does not show a strong trend over time but large annual variations in the outmigration timing. We also investigate if there is a mismatch between salmon smolts and their prey, where the zooplankton (N. plumchrus) or phytoplankton bloom are used as a surrogate for prey. The dates of the phytoplankton bloom were derived from a one-dimensional biophysical model or from satellite imagery. This study provides a quantitative estimation of the phenological shifts of coho and sockeye salmon smolt outmigration timing and of the importance of a mismatch with their prey on their marine survival.