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Invasive Green Crab found on San Juan Island by citizen science volunteers

Earlier this week in Westcott Bay on  San Juan Island, a team of volunteer monitors caught an invasive green crab (Carcinus maenas), marking the first confirmation of this global invader in Washington’s inland waters.


European Green Crab found in Willapa Bay, WA. Photo by P. Sean MacDonald, Courtesy of Washington Sea Grant.

The volunteers are part of Washington Sea Grant’s (WSG) Crab Team – an early detection and monitoring program to look for European green crab and collect information on local marine life.

Washington Department of Fish & Wildlife (WDFW) is responsible for controlling aquatic invasive animals and is working closely with WSG to determine next steps for limiting further spread of the crab. The work is funded by the United States Environmental Protection Agency under Assistance Agreement to WDFW.

European green crab have been stowaways on ships bound for U.S. ports since the 1800s, establishing populations, eating local clams and other shellfish, and causing serious impacts. In Maine, for example, softshell clam harvests declined dramatically when the crab became established and eelgrass beds have been damaged by the invader’s digging habits. Until now, green crab populations in Washington have been limited to Pacific coastal estuaries. However, the 2012 discovery of invasive crabs in Canadian waters across the Strait of Juan de Fuca prompted WDFW investment in Salish Sea monitoring and early detection.

This week’s sighting was confirmed by green crab experts P. Sean McDonald, University of Washington (UW) and Sylvia Yamada, Oregon State University. A single, large, 3-inch adult male crab was captured during the Crab Team’s regular monitoring activity. WDFW and WSG are coordinating a response to the sighting, working with scientists at UW’s Friday Harbor Labs. McDonald, who serves as the Crab Team Science Advisor, called for action to “immediately expand and intensify trapping in the area and build capacity for future monitoring.”

Jeff Adams, WSG marine ecologist and project manager summarized the situation. “Although unexpected and unwelcome, this finding is a perfect example of how volunteers can spur positive environmental action, and it shows that the monitoring program is working as it was designed.”

Crab Team volunteers were trained and began monitoring sites in April to detect the invasive threat and monitor Puget Sound pocket estuaries that provide ideal crab habitat. The WSG monitoring program focuses on early identification of infestations so that resource managers can take action to reduce impacts and prevent further spread.

With an estimated 400 potentially suitable sites in Washington’s inland waters, experts are sounding a call to action for all citizens to keep their eyes open for green crab whenever on the beach. Program coordinator Emily Grason points out that, “Anyone can go out and look for the crabs in the water or their shells washed up along the shoreline.” Although the crab is a prohibited species in Washington and possession is not permitted, residents can still help:

1. Learn how to how to identify green crab. Check out the Crab Team webpage at wsg.washington.edu/crabteam or Facebook and Twitter @WAGreenCrab.

2. Take a photo and report sightings to the WSG Crab team at crabteam@uw.edu.

3. Attend a public presentation by the Crab Team at UW Friday Harbor Labs on San Juan Island Tues., Sept. 13, 7pm. See the Crab Team webpage for additional details.

This project has been funded wholly or in part by the United States Environmental Protection Agency under Assistance Agreement PC 00J29801 to Washington Department of Fish and Wildlife. The contents of this document do not necessarily reflect the views and policies of the Environmental Protection Agency, nor does mention of trade names or commercial products constitute endorsement or recommendation for use.

Washington Sea Grant, based at the University of Washington, provides statewide research, outreach and education services addressing the challenges facing our ocean and coasts. The National Sea Grant College Program is part of the National Oceanic and Atmospheric Administration, U.S. Department of Commerce. www.wsg.washington.edu.

Join the conversation: WASeaGrant and Facebook.com/WaSeaGrant. Crab Team Facebook.com and Crab Team Twitter 

How to identify the green crab.

Don’t let the name fool you; the “green” crab’s carapace (back shell) color can vary widely. Several native Northwest crabs are also green. Adult green crab are about 3” across at the largest part of their shell, making them smaller than adult Dungeness and rock crabs. The European green crab is the only crab likely to be found with five spines along the forward edge of on the back shell from each eye to the widest point; native crabs either have more or fewer spines. Check out Identifying Green Crabs on the Crab Team website for more details on how to recognize this species.

Report potential green crab sightings to the WSG Green Crab Team by emailing mailto:crabteam@uw.edu. Attach any photos of the crab to the email. Take several pictures from different angles and distances to aid in confirming the identification. You will be contacted if any additional information is needed. Please be aware that it is illegal to possess a live green crab in the State of Washington without a special permit, so leave behind any crab you find. Under no circumstances should you harm or kill the crab.

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