Assessment and Management of Salish Sea Herring

Executive summary

Pacific herring are a critical species in the Salish Sea ecosystem, with broad connections throughout the food web. Evidence suggests that some herring are resident in the southern Salish Sea, though evidence suggests an oceanic component to the life cycle for many stocks. As a result, herring represent a significant annual influx of carbon to the Salish Sea, providing energy to lower trophic levels (egg predators) as well as to upper trophic levels (predators of larvae, juveniles, and adults). Herring are also a culturally important species for Native Tribes and First Nations in the region, and are economically valuable to commercial fisheries in British Columbia (BC) and in Puget Sound (PS). While herring biomass in the Strait of Georgia, BC, is near historical high levels, many of the stocks in PS have declined over the past 40 years, with the greatest reduction (nearly 97%) occurring in the Cherry Point stock, once the most abundant in US waters. Additionally, some spawning locations in the southwest Strait of Georgia (SoG) that were occupied for decades have ceased to be utilized in recent years. Developing a coherent regional management strategy for the whole of the Salish Sea requires coordinated research and monitoring between herring users and stakeholders, and across international boundaries.

Meaningful, effective action to recover fish and wildlife populations occupying the Salish Sea must be informed by the best available science, be cognizant of the programmatic, policy, and management contexts within which recovery actions occur, and acknowledge interactions among ecological, economic, and social components of the ecosystem. While a Forage Fish Management Plan was developed by the Washington Department of Fish and Wildlife and its partners in 1998, followed by a Forage Fish Ecosystem-based Management Study Panel convened in 2013 by the Puget Sound Institute, at present there are no specific strategies for reaching recovery targets for Pacific herring stocks in Puget Sound (PS), and such strategies must be developed by a multi-institutional, transboundary, interdisciplinary recovery team that recognizes the regional socio-ecological context of forage fish resources at large.

To advance conservation and management of Pacific herring in the Salish Sea, an Assessment and Management Strategy Team (the Team) was convened, composed of representatives from government agencies from Washington and BC; social and natural scientists from universities, First Nations, and Tribes; and other stakeholders. The Team performed an expert data elicitation to assess the historic and current status of herring stocks in the Salish Sea and compile a library of relevant publications and grey (unpublished) data. Furthermore, we asked members of the Team and their colleagues to evaluate the state of knowledge, and synthesize their experience and knowledge to provide hypotheses regarding the influence of specific stressors on herring population declines and limitations to recovery, assess ongoing monitoring and management programs for herring and these stressors, and identify priority actions and key uncertainties that must be addressed to advance herring conservation and sustainable management. 

Responses from the elicitation were used to develop a Salish Sea-wide conceptual model of factors affecting herring populations and a qualitative network model (QNM) that serves as a heuristic tool for assessing potential management actions and strategies by simulating herring population responses to variation in the relative intensity of key stressors under various scenarios. At a two-day workshop, the Team and a diverse panel of stakeholders considered the state of our compiled knowledge, the two models, and the ability of the QNM to adequately simulate effects of possible management actions. Broad consensus about the cultural and ecological importance of herring, and the nature and relative extent of stressors, existed but some regional differences in stressor intensity and impact were noted. While the conceptual model was sound, the QNM was substantially recast and reparameterized as a result of feedback from this workshop. Further development and performance testing of the QNM will occur in coming months, but it is presented here in a form that can be tailored to location-specific needs and used to evaluate potential changes in stressor intensity or prevalence as a result of management actions.

Urbanization and coastal development, predation, and compromised water quality were the primary factors identified as both suppressing population levels and limiting recovery potential, and an extensive suite of priority actions associated with comprehensive monitoring and research were identified.

Priority Actions Over the next 12 months, convene the Team and other regional experts to develop approaches for testing solutions to primary threats, including increasing egg survival rates at critical herring spawning sites, such as Cherry Point and the San Juan Islands; reducing noise at spawning sites during critical times; identifying hot spots of adult herring predation; and improving habitat quality for nearshore-dependent life stages. 

Trends in the abundance and distribution of Salish Sea herring observed are:

●    Decrease in adult spawner abundance (measured via egg surveys) in some Puget Sound stocks
●    Change in distribution among Strait of Georgia stocks, north- and west-ward, including a loss of some south and eastern spawning sites
●    Change in distribution among Puget Sound stocks, including a decrease or loss of some southern spawning sites
●    Vulnerability to depensatory dynamics, including from fishing and other pressures

Threats to Pacific herring populations identified as common across the Salish Sea include

●    Predation by marine mammal populations undergoing population increases (Harbor seals, Harbor porpoises, sea lions, humpback whales)
●    Noise from vessel traffic
●    Water quality degradation
●    Habitat degradation, including loss of submerged vegetation and shoreline hardening
●    Cumulative impacts of shoreline development, including noise, ambient light, poor water quality, and habitat degradation

Threats to Pacific herring populations identified as unique to areas of the Salish Sea

●    Contaminants that increase embryo mortality and embryo and larval malformations (Puget Sound)
●    Fishing that may cause local extinctions when interacting with populations having certain migration patterns (Strait of Georgia)

Management actions that may be possible to implement

●    Protect eggs from predation by birds
●    Reduce vessel noise (current priority of Washington State Governor’s Southern Resident Killer Whale task force)
●    Reduce risk of oil spills (current priority of Washington State Governor’s Southern Resident Killer Whale task force)
●    Reduce contaminants (piling removals, and via Puget Sound Toxics in Fish Implementation Strategy)
●    Improve water quality (via Puget Sound Marine Water Quality Implementation Strategy)

Management actions that are more difficult to implement

●    Reduce predation by pinnipeds
●    Reduce light pollution
●    Modify hatchery salmon release timing to reduce competition from forage fish

The data compilation and evaluation effort presented here considers the suite of ecosystem and socioeconomic benefits provided by herring in the Salish Sea at large and the importance of population dynamics that occur on local as well as regional scales. It then identifies shared factors influencing, and potentially causing, sustained low biomass and/or lack of stock vitality in some locales and identifies key uncertainties, research, and monitoring needs that can be addressed to promote long-term, sustainable management. Finally, it produces a pair of models that can be used to consider how changes in the intensity and extent of identified stressors as a consequence of specific management actions are likely to affect herring population status. This represents the first time that such a foundation for comprehensive management strategy evaluation pertinent to Pacific herring has existing for the full extent of the Salish Sea. 
 

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