Phenological diversity of a prey species supports life-stage specific foraging opportunity for a mobile consumer

Y Dynamic prey resources influence foraging opportunities for consumers. In coastal food webs, forage fish abundance and seasonal reproduction mediate foraging opportunities for mobile consumers. Recent declines in Chinook salmon productivity have prompted efforts to determine whether poormarine survival is caused by limited feeding opportunities. To establish the importance of phenological diversity in Pacific herring for Chinook salmon, we used genetic stock identification to assign individual herring collected from the guts of juvenile and adult Chinook salmon to populations with distinct spawning phenologies. The majority of herring in the guts of adult Chinook salmon across seasons and geographic areas were dominated by the March-April herring spawn group, but juvenile Chinook salmon diets varied seasonally, with a higher proportion of January-February spawners in summer than in spring. Our results suggest that (1) population diversity of Pacific herring is used by juvenile Chinook salmon and thus contributes to their growth, and (2) stock-specific distribution of Pacific herring extends well beyond documented spawning grounds. Herring population diversity may therefore support foraging opportunities for Chinook salmon during a critical period and highlights the need for future research to quantify seasonal distribution and abundance of phenologically distinct groups of Pacific herring within Salish Sea.