Print PagePacific herring (Clupea pallasi) are integral to coastal social-ecological systems in North America. This migratory species connects marine ecosystems by moving from offshore to nearshore waters for annual spawning events, providing a key source of food for coastal predators, and supporting subsistence and commercial fisheries for coastal communities. While land-sea ecological linkages via anadromous fish have been well documented, connections between marine systems via fish subsidies have not received focused research attention.
In the 20th century, herring experienced dramatic fluctuations in abundance and catch in many areas of British Columbia, Canada. The Herring School research group (Hakai Network, SFU), in conjunction with community partners including the Heilstuk First Nation, address questions pertaining to the causes and consequences of changes in herring populations. Our ecological research program aims to understand the effects of this pulse subsidy on ecosystem structure and processes. Currently, studies have focused on effects of herring spawning on rockfish (Sebastes spp.) populations and the loss of eggs from nearshore subtidal systems by predation and other physical factors. Our studies on rockfish dynamics have focused on stomach content analysis, and we use an experimental design based on the traditional Spawn on Kelp fishery to quantify egg loss rates associated with predation and water column depth.
Results/Conclusions
We found the first evidence of direct herring roe consumption by rockfish. Pre-spawn, rockfish consumed fish (55% stomach volume) and invertebrates (45% stomach volume). Diet switched following a spawn event, with roe and roe-on-algae accounting for > 60% of average fish stomach volume. The effects of herring egg predation were further substantiated in the Spawn on Kelp experiment. Here, we found that predation significantly increased herring egg loss. Un-caged samples experienced a greater average percent egg cover loss rate than those protected from all predators. Furthermore, average egg loss in the benthic environment was greater than that on the surface.
These studies are crucial for implementing ecosystem-based considerations into management of this fishery. Furthermore, herring stock abundances may be underestimated given the significant loss of eggs following spawn events. Adjusting spawn survey estimates with a daily egg loss rate would reduce the uncertainty in current stock models. The quantitative field ecology portion of this project will be coupled with archaeological 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.
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