The Role of Egg Predation in Pacific Herring Population Dynamics in Puget Sound, Washington

Forage fish such as Pacific herring (Clupea pallasii) are ecological foundation species in marine and estuarine ecosystems. In the Puget Sound estuary, Pacific herring are an indicator species, and the regional management agency has set recovery targets to guide herring management. Puget Sound herring are spatially and temporally segregated into individual subpopulations by their spawning behavior, and these subpopulations show asynchronous abundance trends over the past several decades. Some local spawning subpopulations have significantly declining trends. Here we focus on the embryonic stage as a potential limiting stage for herring, assessing the relative importance of predation in determining herring egg hatch success, and the implications of predation rates for observed local trends in herring biomass. Using a combination of in situ incubations and predation exclusion devices, we estimated herring egg survival rates both in the presence and absence of large predators, across multiple spawning subpopulations in Puget Sound. We found that predation accounted for approximately 50% of egg loss across all spawning populations. We link predation rates to 40+ years of herring biomass estimates for each spawning population and trends in major egg predators (diving ducks) to develop hypotheses about leading pressures on herring populations in Puget Sound.