Shedding light on Dungeness crab in Washington
For over 20 years, Sean McDonald (Associate Teaching Professor for the UW Program on the Environment) has been working on West Coast crab populations. Among his favorite study subjects is the Dungeness crab. Despite its very high value both commercially and culturally, scientists know surprisingly little about the iconic crustacean’s early life.
Gaps in knowledge about the species are particularly evident in the Salish Sea, a vital inland water body spanning Washington State and British Columbia. Declines in historically productive areas have led to fishery closures and raised concerns about population status and sustainability. Questions also remain about the species’ vulnerability to stressors such as overfishing. Addressing these challenges requires a deeper understanding of the ecological and environmental factors influencing Dungeness crab populations to ensure the long-term viability of this critical fishery.
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- From larvae…
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- …to adult.
In a collaborative effort spanning federal agencies, local government, tribes, non-profits and scientists, the Pacific Northwest Crab Research Group (PCRG) has been undertaking a monitoring effort along the Washington coast for larval Dungeness crab. Every other day from April to September, researchers go into the field to monitor for pulses of Dungeness larval crab.
“Shedding light by using light” – this is how Sean described the light trapping techniques used by scientists where containers that use LED lights are placed in the water and attract larval crabs, like moths to a flame. This work is designed to help PCRG researchers understand the dynamics of Dungeness crab populations and where they come from, where they are going, and what factors impact these movement patterns.
New work, published in January 2025 in Fisheries Magazine, provides early insight gleaned from this effort. Larval crab abundance consistently peaks in June and July each year and tends to be consistently higher in the central Salish Sea and north Hood Canal. However, South Puget Sound tells a different story, with populations struggling to establish this area as a home. Part of the objective of larval monitoring about movement and abundance is to develop projections for what the population might do four to five years down the line and help inform management decisions for the fishery.
One of the hypotheses that scientists want to understand more deeply is whether or not the lack of Dungeness crab in South Puget Sound is a result of the lack of larvae supplied by ocean currents. Observations suggest this is the case, backed up by monitoring data and fisheries data, with patterns of abundance of adult crab reflecting hotspots for larvae.
These discoveries would not be possible without the dedicated efforts of staff and volunteers working to monitor Dungeness crab larvae. The Shilshole Marina site, one of 43 sites across Washington and British Columbia where the monitoring program takes place, is 100% staffed by UW students from the Program on the Environment, School of Aquatic and Fishery Sciences, and Marine Biology units.
“I’ve sampled at Shilshole Marina for 2 seasons now, and I’ve enjoyed getting familiar with the different larval stages of Dungeness crab, as well as other zooplankton species we can identify,” said Ellie In, a Marine Biology major in her junior year. “There’s no better way to learn what zoea, megalopae, and instars look like than holding them and seeing them up close.”
Going out in small teams every other day, the team of students sort through samples to count numbers of Dungeness crab. This work is important for scientific research, but it also has a significant educational function by providing hands-on training for students in fieldwork and managing projects, building skills for their current studies and future careers.
If you are a UW student interested in participating in monitoring for the 2025 season, apply here. Priority application deadline is March 1. Contact psean@uw.edu with questions.
“Collaborating with my peers at the Shilshole site was a fantastic opportunity to explore new data collection techniques, assist PCRG, and discover new marine life,” said Sam Eck, a third-year Marine Biology student. “One of the highlights for me was contributing to the media folder with photos and videos from my camera. It was always a thrill to return home and review the footage of what we had pulled up in the trap.”
“Through this experience, I learned how to collaborate with other students while doing field work. I gained hands-on experience identifying different species through the variety of marine organisms caught in the light trap,” shared Sophia Eckhart, a Marine Biology senior.
