Participatory modeling to evaluate tribal pinniped harvest in Puget Sound as a tool for salmon recovery

Abstract

Pinnipeds and salmon have been actively managed by tribes in the Salish Sea since time immemorial. Tribal pinniped harvest impacted pinniped populations directly through removals, indirectly through disturbance, and spatially by excluding them from frequently utilized areas near village sites, which often included important salmon migration routes. Current management practices struggle to balance pinniped recovery success with the need to protect the threatened salmon populations they prey on. We employed a Participatory Modeling Process to collaboratively develop a modeling framework with treaty tribes in Western Washington that could explore the impacts of pinniped management scenarios on the survival of returning adult salmon in terminal areas. We developed a model that simulates the dynamics between pinnipeds and salmon using a combination of agent-based and dynamic components to represent aspects of pinniped behavior, foraging decisions, fear conditioning, individual learning, and social contagion. Using this model, we explored different management regimes for pinniped harvest and evaluated success by monitoring the number of salmon who survive predation by pinnipeds and are therefore available to fulfill other management objectives. We carried out these simulations in two case study locations: the Ballard Locks in collaboration with the Muckleshoot Indian Tribe, and the Nisqually River in collaboration with the Nisqually Indian Tribe. We found that management scenarios where pinniped management was carried out in a way that allowed pinniped predators to develop fear of management activity were more effective at improving salmon survival. We also identified specific scenarios for each case study that benefitted the specific salmon runs that use those systems and described the general characteristics of successful management strategies. The results from this study will be used by our partners in tribal resource management agencies to structure pinniped management in their Usual & Accustomed areas and identify data gaps for future monitoring efforts. Providing pathways for tribes in Washington to exercise their treaty rights to harvest pinnipeds in a way that mitigates salmon predation hotspots could be an effective management strategy that balances complex conservation objectives while operating within existing legal and political frameworks.