Covariability of Fraser River sockeye salmon productivity and phytoplankton biomass in the Gulf of Alaska

Using satellite ocean color measurements and sockeye salmon stock-recruit data from 1995 to 2016, our analysis reveals a significant, positive relationship between Fraser River sockeye productivity and summer chlorophyll a concentrations (Chl-a) in the northwestern Gulf of Alaska. The correlation is the strongest for the area adjacent to the continental shelf near Kodiak Island (northern Gulf of Alaska), during midsummer of the juvenile sockeye salmon ocean entry year. The inclusion of (Chl-a) data from this region significantly improved the performance of Ricker stock-recruitment models for ten out of eighteen Fraser River stocks. We discuss the potential oceanographic processes driving the correlation between (Chl-a) and sockeye productivity. During midsummer, positive sea-level anomalies in the offshore waters near Kodiak Island suggest the presence of mesoscale eddies, which can transport nutrients to this region and concentrate phytoplankton and zooplankton biomass, thus supporting enhanced sockeye salmon prey abundance. These results suggest a mechanism linking mesoscale oceanographic dynamics to sockeye salmon productivity, and identify a potentially important region for future studies of Fraser River sockeye salmon survival.

Automated summary

Through satellite ocean color measurements and sockeye salmon stock-recruit data analysis, a significant positive correlation between Fraser River sockeye productivity and summer chlorophyll a concentrations in the northwestern Gulf of Alaska has been revealed. The strong correlation, particularly near Kodiak Island in the northern Gulf of Alaska during midsummer, suggests the potential impact of mesoscale oceanographic processes on sockeye salmon prey abundance and productivity. These findings highlight the importance of considering ocean dynamics in understanding sockeye salmon survival and identify a key region for future research.