The Socio-ecological Role of Pacific Herring (Clupea pallasi) in Nearshore Ecosystems

Pacific herring (Clupea pallasi) are an integral component of temperate marine ecosystems in North America. This migratory species connects marine ecosystems by moving from offshore to nearshore waters for annual spawning events. In doing so, this commercial fish stock provides a key source of food for coastal predators, and supports subsistence and commercial fisheries for coastal communities (sac roe and spawn-on-kelp fisheries). In many areas along the coast of British Columbia (B.C.), Canada, this fish species has experienced dramatic fluctuations in abundance throughout the past century. In many regions, declining biomass trajectories have been observed during the past decade. This has prompted coastal communities and scientists to examine the strength of evidence for alternative ecological and socio-economic drivers of these trends, and their potential consequences on nearshore ecosystems. This research group (The Herring School), uses a multi-disciplinary framework to address these questions, with preliminary research focused on ecological questions. Herring transport marine nutrients and biomass, acquired during the pelagic phase of their life cycle, to coastal marine systems, where they deliver roe and milt to nearshore systems during annual spawning events. The effects of this pulse subsidy on community-level dynamics and ecosystem processes has not been well studied, empirically, in subtidal systems. We quantified the effects of herring spawn on fish communities using abundance surveys and stable isotope analysis and found that both fish diet (Rockfish and Greenling) switched post-spawn to include herring roe. Changes in tissue isotope values were species-specific, and primarily apparent in liver tissue. Primary production, an important ecosystem-level process, was also measured using macroalgal growth assays. Evidence for herring spawn effects were also documented for kelp growth rates, and were associated with water column light attenuation and nutrient concentrations. The Herring School research program is conducted in collaboration with the Heiltsuk First Nations, in the Central Coast region of B.C. The quantitative field ecology portion of this project will be coupled with archeological and traditional use data, quantitative time series modeling and a governance system analysis to inform the conservation and management of herring populations and the ecosystems in which they are embedded.