POPULATION GENETICS

Are Puget Sound Dungeness crab one large population or part of multiple, genetically distinct populations?

An early research priority of PCRG was to assess whether Dungeness crab management areas in Puget Sound were aligned with biologically relevant information such as the presence of genetically distinct sub-populations. Previous research, as well as the PCRG larval crab monitoring network, have observed the existence of at least two morphologically distinct recruitment cohorts in Puget Sound (Orensanz and Gallucci 1988; DeBrosse et al. 1990; Dinnel et al. 1993; Cook et al. 2024; Buckner et al. 2025) and some genetic differentiation in crab between Puget Sound sub-basins (Jackson and O’Malley 2017). Around 700 larvae and 600 adult Dungeness crab were sampled in 2023 and analyzed using low coverage whole genome sequencing to look for 1) relationships in larval size and timing with genetic signature and 2) relationships between adult location (i.e which management region they were caught in) and genetic signature.

The study is still underway, but so far it has found that Dungeness crab in the Salish Sea are generally well-connected with the outer coast. However, this connection does weaken north of the San Juan Islands and south of Port Townsend. These patterns match long-term observations of where and when crab larvae are caught in the region and can be explained by differences in when crabs hatch and how water circulates within the Salish Sea.

Adult crab genetics: Coastal crab signature (red) strong in Strait of Juan de Fuca but weakens in Puget Sound and Strait of Georgia.

We also examined why young crabs differ in size. Crab larvae that arrive in the Salish Sea early in the season are consistently larger than those that arrive later. Our genetic analyses, together with environmental data and the results of older laboratory rearing studies, suggest that these size differences are likely to be primarily caused by temperature, rather than genetics, with cooler waters producing larger crab larvae. Interestingly, it is possible that these temperature conditions experienced during early life can cause different growth rates that persist into adulthood. This is an interesting avenue for further research.

An increase in sea surface water temperature (SST, x-axis) correlates with decrease in larval size (y-axis).

Together, these findings show that both where crabs come from and how environmental conditions affect their growth can have important consequences for crab populations and fisheries. Understanding these patterns is critical for effective and sustainable management of the Dungeness crab fishery in Washington.

Principal Investigators: Dr. Jay Dimond (Western Washington University, Sarah Grossman (Swinomish Indian Tribal Community), Dr. Katelyn Bosley (WDFW), and Dr. Elizabeth Tobin (Jamestown S’Klallam Tribe)

Funded by the U.S. Fish & Wildlife Tribal Wildlife Grants and the NOAA Saltonstall-Kannedy Program