UW News

September 2, 2016

Invasive green crab found on San Juan Island by citizen science volunteers

Washington Sea Grant

a green crab

A European green crab (Carcinus maenas, meaning “raving mad crab”) found earlier in Willapa Bay, Washington.P. Sean McDonald/Washington Sea Grant

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

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

Washington Department of Fish and Wildlife is responsible for controlling aquatic invasive animals and is working closely with University of Washington-based Washington Sea Grant to determine next steps for limiting further spread of the crab.

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 the state’s wildlife department to invest in Salish Sea monitoring and early detection.

This week’s sighting was confirmed by green crab experts P. Sean McDonald of the UW and Sylvia Yamada of Oregon State University. A single, large, 3-inch adult male crab was captured during the Crab Team’s regular monitoring activity. The agencies are coordinating a response to the sighting, working with scientists at the UW’s Friday Harbor Laboratories.

volunteers checking for green crabs

Crab Team volunteers assess shoreline vegetation on San Juan Island, Westcott Bay, as part of monthly monitoring.Emily Grason/Washington Sea Grant

“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,” said Jeff Adams, Washington Sea Grant marine ecologist and project manager.

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 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 asking all citizens to keep their eyes open for green crab whenever on the beach.

“Anyone can go out and look for the crabs in the water or their shells washed up along the shoreline,” said program coordinator Emily Grason.

Although the crab is a prohibited species in Washington and possession is not permitted, residents can still help:

  • Learn how to how to identify green crab. Check out the Crab Team website or Facebook and Twitter: @WAGreenCrab
  • Take a photo and report sightings to the Crab Team: crabteam@uw.edu
  • Attend a public presentation at UW’s Friday Harbor Labs on San Juan Island at 7 p.m. Tuesday, Sept. 13. See the Crab Team website for additional details

The work is funded by the U.S. Environmental Protection Agency under an assistance agreement to Washington Department of Fish and Wildlife.

Note: The video above shows an invasive green crab found last month in Willapa Bay.


For more information, contact McDonald at 206-616-2186 or psean@uw.edu; Adams at 360-229-9398 or jaws@uw.edu; and Jason Wettstein, community relations at Washington Department of Fish and Wildlife, at 360-902-2254 or James.Wettstein@dfw.wa.gov.