Scientists monitor juvenile European green crab populations in Drayton Harbor

Scientists are keeping a close eye on Drayton Harbor waters after discovering a sizable population of juvenile European green crabs, indicating growth of the highly invasive species. 

In 2022, scientists found 313 European green crabs, about half of which were juveniles, said Allie Simpson, ecosystem project coordinator for the Northwest Straits Commission. Many of the juvenile crabs were found in a small creek between Dakota and California creeks last September and October.

The crabs are considered one of the world’s worst invasive species and are known to destroy salmon habitats, such as eelgrass, and are a threat to shellfish and aquaculture industries.

Scientists have found just over 100 crabs in Drayton Harbor since this year’s trapping season began in the spring, Simpson said. Slightly more crabs have been caught compared to this time last year.

Emily Grason, crab team program lead at Washington Sea Grant, said the warm fall last year allowed scientists to capture crabs later than usual. 

“In some cases, sites in Whatcom and Skagit were reporting the highest capture rates during the final capture efforts of the year,” Grason said. “Many groups weren’t ready to stop trapping because there were clearly crabs out there. You want to see the decline in capture rates before pulling your traps out of the water.”

Those juvenile crabs made up the lion’s share of captured green crabs when trapping resumed after winter, Grason said. She added this could be a positive sign because it shows previous trapping has worked if more mature crabs are not being found.

The Northwest Straits Commission, University of Washington’s Washington Sea Grant program and Washington State Department of Fish and Wildlife, with help from other partners, are leading the fight against the spread of European green crabs in Drayton Harbor and across the state. From spring through fall, the crews trap at the old Cherry Street pier and the mouths of Dakota and California creeks. Scientists also survey other areas near Drayton Harbor.

The 313 crabs found in 2022 is more than in 2021 and 2020, which yielded 146 and 253 crabs respectively. 

“Even though the numbers in Drayton Harbor are increasing, they’re still very, very low compared to other places,” Simpson said. “We’re still at the early stage of containing the green crabs and making sure we’re dropping those numbers.”

Simpson said the higher crab numbers may indicate scientists are improving their methods through knowing where to trap and using more effective trapping techniques.

“The trapping levels we’ve been able to have has really helped,” Simpson said. “Even though the numbers look crazy, the number of green crabs we catch are less than one percent of the total number of animals we end up trapping.”

Despite the presence of green crabs, they have not caused ecological damage to Drayton Harbor, Simpson said.

The statewide fight

Green crabs were discovered in Washington state in 1998, but it wasn’t until 2018 that scientists began seeing an increasing number, and 2019 when they were discovered in Drayton Harbor. WDFW attributes rising water temperatures as a likely reason why the crabs started appearing.

Scientists have been working to combat green crab infestations along the coast in southern Washington as well as keeping more manageable populations at bay in Whatcom, Skagit and San Juan counties. The state, tribal and local governments have taken numerous actions over the past few years to assist with the green crab fight – including an emergency proclamation that governor Jay Inslee issued in January 2022 and a disaster declaration that Lummi Business Council issued in late 2019 after over 70,000 crabs were found in a Lummi sea pond.

Washington state scientists are working to prevent significant damage, as seen on the east coast, where green crabs are widely thought to be jeopardizing Maine’s soft-shell clam industry.

Citizen scientist program

Washington State University’s extension offices partnered with Washington Sea Grant this year to create a European Green Crab Molt Search program for the public to help monitor shorelines. The program will hold its last training of the year virtually on Wednesday, August 23. 

The training will teach the public to identify invasive and native green crab molts, where to search and how to upload their photos on the MyCoast app. The session will be held from 11 a.m. to 1 p.m. on Zoom. 

Statewide, the molt search program has trained about 250 volunteers and 22 of those volunteers are in Whatcom County, Grason said. The program has not detected a green crab in the over 200 reports it’s received since starting in May, which Grason said is a good sign.

“This program enables us to cover more ground than we can with trapping, so these searches are filling in gaps on places we haven’t yet had a chance to look,” she said.

Cheryl Niles, water resources educator at Washington State University’s Whatcom County extension, said program organizers have been pleased with the number of submissions. Niles recommended people visit the MyCoast website, where participants upload molt photos, to see where people have searched and try to cover new ground. 

Niles encouraged program participants to receive training. 

“It is easy to misidentify crabs so we are really encouraging people to get trained,” Niles said. “That said, anyone can download the MyCoast app and submit a report if they know their crabs.”

Green crabs can be identified by five spines on both sides of their eyes, a characteristic that separates them from other crabs in the state. Despite their name, the crabs can vary in color from green, red, brown and orange. The crabs are typically found in protected areas along the shore, such as mudflats and river mouths. 

Drayton Harbor residents who own land next to creeks can also help scientists by allowing access to trap on their properties, Simpson said. Landowners can contact Allie Simpson at simpson@nwstraits.org. 

“We’ve found them pretty far up, at times, in California Creek and Dakota Creek,” Simpson said. “The more that we can access and see where they are congregating would be a huge help to getting numbers down.” 

Both Simpson and Grason said trapping will be a continuous effort for years to come.

“Now is not the time to let our foot off the gas pedal in terms of trapping because we are keeping the numbers low,” Grason said. “The numbers tell us our efforts are having a large effort on what could have been a much worse situation.”

To register for the European Green Crab Molt Search program, visit bit.ly/VirtualMoltSearch.