Pacific herring (Clupea pallasii), a major forage fish species in the eastern Pacific Ocean, are key prey for many marine species throughout their range, including for threatened salmonid species in Puget Sound. Puget Sound herring spawning stock biomass has been declining locally over the past 40 years, including the San Juan Island spawning populations. Salmon in the area of the San Juan Islands have been found to be particularly reliant upon herring for prey. At present, while there are many hypothesized causes of herring declines, there is little agreement on the primary cause or, therefore, the best management or policy actions for recovery. Lead Ecologist Tessa Francis is leading a 3-year effort to address this gap in understanding through 3 primary activities: (1) convene an expert elicitation workshop to evaluate key threats to San Juan Island herring; (2) quantify changes in the abundance and distribution of eelgrass used as spawning habitat for San Juan Island-spawning herring using historical data; and (3) monitor herring spawning sites to measure early-life-stage (i.e. embryonic) mortality rate.
In November 2017, Francis, with colleagues from the Washington Department of Fish and Wildlife, convened an expert workshop to evaluate hypotheses about declines in herring in the Salish Sea, including the San Juan Islands. At present, Francis is developing a Qualitative Network Model to evaluate the relative support for different hypotheses about what is causing herring declines.
Habitat modeling, based upon a spatial model developed by NOAA scientist and PSI collaborator Ole Shelton, will be conducted in 2018. Field work is planned for the herring spawning season in 2019.
Fig. 1. Site-scale changes in eelgrass area at herring spawning sites in Puget Sound. This project supports the analysis of these patterns in the San Juan Islands. From Shelton et al. 2017.