A participant from the Molt Search program made the important Discovery

November 25, 2025

La Conner, Wash. — In late September, the molt from a European green crab was found at Similk Beach, on the northern end of the Swinomish Tribal Reservation. This was the first detection of the highly invasive species in the northern Whidbey Basin, which includes Skagit Bay.

Community member Shirley Hoh made the discovery while participating in a routine search as part of Molt Search, a volunteer-based early detection program from WSG Crab Team and Washington State University Extension. Launched in 2015 in response to a Washington Department of Fish and Wildlife (WDFW) mandate to monitor for European green crabs along inland Washington shorelines, WSG Crab Team has a long track record of using community science for early detection of green crab invasions.

Upon receiving the report through the Molt Search app, WSG Crab Team, WDFW, and the biologists from the Swinomish Indian Tribal Community (SITC) met to plan and carry out a trapping effort. “We found a concerning number of European green crabs,” says Emily Grason, WSG Crab Team program lead. Based on the size of the crabs, the group could tell the crabs had been there for at least a couple of years. SITC led several additional follow-up trapping efforts, and a total of 12 green crabs have been captured across three sites in Skagit Bay.

The crab detections present a double-edged sword. On the one hand, it is further evidence of the spread of green crab in Puget Sound — a species that has disrupted ecosystems, shellfish harvests and fisheries worldwide. On the other hand, it is evidence that the Molt Search program, which launched in 2023, is successfully working. “This is exactly what Molt Search was designed to do — fill in the places where people aren’t currently trapping for green crab, and leverage other ways of looking for evidence that green crab might be there,” Grason says.

In its early days of trapping, the Crab Team monitoring network found some of the first generations of green crabs to land on inland shorelines. Over the years, Crab Team has grown to broadly support green crab management needs in Washington through partnerships and advising with agencies, Tribes and local trapping efforts.

However, while trapping is one of the more sensitive ways to detect relatively small populations of green crabs, it is logistically and labor-intensive, meaning Crab Team and partners can’t establish trapping sites at every single location where green crabs could arrive. That’s where Molt Search comes in — by looking for the exoskeletons that crabs shed as they grow, anyone walking a beach can help be on the lookout for signs that green crabs might be nearby. “Molt Search’s simple protocols enable hundreds of community members to build on the efforts of managers and trappers also looking for green crab across Washington shorelines” says Lisa Watkins, WSG community science specialist.

Less than two months prior to Hoh’s find at Similk Beach, the Tulalip Tribes found a green crab on Mission Beach in Possession Sound. This was the first detection of a green crab in the southern end of Whidbey Basin, at the opposite end of the basin from Skagit Bay where Hoh found a shell from the same invasive crab species. Tulalip Tribes followed up the find on Mission Beach with a “trapping blitz” — setting 110 crab traps — but found no further green crabs in that region of Whidbey Basin.

Grason had originally expected the northern part of the Basin would be more protected from a green crab invasion than Mission Beach because of the narrow inlet to the area that is Deception Pass. “It turns out that crab larvae coming into the Strait of Juan de Fuca can get shot right through Deception Pass,” Grason says. This is something she learned from WSG Crab Team partners with the Swinomish Tribe, through their work studying Dungeness crab. The partnership between WSG Crab Team and the Swinomish Tribe is long standing: in fact Molt Search protocols were adapted from the Tribe’s work on Dungeness crab sampling (Hoh also volunteers for that effort), which were in turn adapted from the Crab Team monitoring network protocols.

The Tribe has also supported Crab Team by enabling access to sites on the reservation and subsidizing the purchase of trapping gear in the early days of the program. “SITC Fisheries Department staff knew that green crab would eventually reach our shores, but it was still disheartening to catch those first few crabs,” says Talia Davis, a fisheries technician with the Swinomish Tribe. “Fortunately, WSG Crab Team and WDFW responded quickly and worked alongside us for our first large-scale trapping event. Their combined green crab knowledge and on-the-ground expertise have been invaluable as we navigate these new detections.” Over time, WSG Crab Team, along with WDFW, has helped the Tribe grow technical skills and capacity to carry out its own green crab trapping efforts.

The green crab findings in the Whidbey Basin are part of an overall trend seen this year of a notable increase in the number of green crabs found in Washington’s inland waters. This is due in part to the 2024 El Nino climate pattern. In some water bodies where green crabs were known to be present, catch rates were particularly high in the spring — consistent with strong population growth during 2024. Additionally, in northern Hood Canal, many new detection sites have been “filling in the gaps” between sites where green crabs had previously been found, including Port Gamble Bay and central Hood Canal.

This goes to show the continued importance of a multi-pronged approach to managing the spread of the invasive species. And the Molt Search program has proven itself a simple yet effective tool to have in the toolbelt.

Learn more about how you can contribute to efforts to manage European green crab.

Media contact: Emily Grason, WSG Crab Team Program Lead, egrason@uw.edu

 

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