Genotypes for herring samples collected from Chinook salmon gut contents

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.