Forecasting central Salish Sea Dungeness crab populations: A study in patience

Dungeness crab (Metacarcinus magister) are an important species in the Salish Sea because they not only supply a lucrative commercial fishery, but they also fill a critical ecological role in marine food webs. Although we have a relatively good understanding of M. magister larval dynamics and the relationships between larval supply and subsequent fisheries landing on the outer coast, fundamental gaps still exist with regard to our knowledge of their early life stages within the Salish Sea. Most notably, how physical drivers influence the annual patterns in larval supply and in turn how larval supply contributes to subsequent fisheries landings. To begin addressing these questions, Swinomish Fisheries is working towards developing a forecast model for Dungeness crab fisheries in the Salish Sea using M. magister larval dynamics as the basis. Starting in 2018, we began monitoring daily abundance of late-stage larval Dungeness crab from April to September at locations in Whidbey and San Juan Basins. To date results reveal highly variable spatial and temporal patterns of larval delivery to these sub-basins. Additionally, within the central Salish Sea, phenotypically-distinct larvae are delivered to the system months apart. Dissimilarities in the timing, size at settlement, and growth rates may have important implications for the community structure of these populations. As we continue with our long-term monitoring program, we will begin to examine the physical drivers that contribute to annual patterns of cohort dynamics, larval abundances, and the growth and survival of young-of-the-year juvenile crab by sub-basin with the goal of developing more biologically appropriate management tools for the Dungeness crab fishery.