Tribal natural resources staff are setting traps for European green crab on the North Olympic Peninsula and Puget Sound, hoping not to find any.
A small number of the invasive crab were found last year in North Puget Sound, apparently not enough to establish a population. However, since April, 60 green crab have been found at a single site near Sequim.
“At Dungeness Spit, multiple crabs are being found at the same site, over successive days of trapping,” said Emily Grason, Washington Sea Grant’s Crab Team program coordinator. “This indicates a situation where the population could grow very quickly, if we don’t intervene.”
Area tribes are partnering with Sea Grant and the Washington Department of Fish and Wildlife’s Aquatic Invasive Species Unit to monitor nearshore habitat to ensure that invasive green crab don’t take over. Tribes involved in the work so far include Jamestown S’Klallam, Stillaguamish, Suquamish and Swinomish.
After the discovery in Dungeness Spit in April, scientists organized to eradicate the crabs there, increasing the trapping from monthly to three or four times a week. The Crab Team will continue to set traps monthly to monitor other areas around Puget Sound.
“From the tribe’s perspective, our goal is to set traps in all the salt marshes in Sequim Bay,” said Neil Harrington, Jamestown S’Klallam Tribe’s water quality scientist. “We don’t want a green crab population establishing itself this summer without us knowing it. To knock that back is really important.”
On the East Coast, the invasive species is blamed for the collapse of the eastern softshell clam industry in Maine. Here, green crab could threaten Dungeness crab, oyster and clam fisheries. They feed on many organisms, including clams, oysters, mussels, marine worms, and small crustaceans. In large numbers, they also would damage eelgrass and degrade nearshore habitat by burrowing into the mud.
A population of green crab was found in 2012 in the Sooke Inlet at the southern end of Vancouver Island, Canada. The Washington Sea Grant Crab Team monitored seven sites in 2015, finding no green crab. In 2016, they surveyed 26 sites in Puget Sound, the Strait of Juan de Fuca and San Juan Islands. One live green crab was found on San Juan Island, along with the molt of a different crab. Four crabs were found at the Padilla Bay National Estuarine Reserve, in Skagit County.
This year, more than 50 sites will be monitored, with the help of volunteers, agencies and tribal natural resources staff.
“After learning that green crabs were found in Padilla Bay last year, Stillaguamish tribal staff signed up for training and offered to support a couple of sites in Port Susan Bay,” said Franchesca Perez, Stillaguamish shellfish biologist. “We have long had good relationships with the volunteers on Camano Island, and were happy to lend our technical skills to their effort to protect our shared ecosystem.”
Port Susan has millions of pounds of eastern softshell clams that would be at risk of predation by green crab, Perez said. Eastern softshells are harvested commercially in South Skagit Bay.
Despite the name, green crab can be other colors. They are most easily identified by five distinct spines on the shell beside the eyes. They can grow up to about three inches across – bigger than most native shore crabs, but not as big as Dungeness crabs.
The only way to eradicate them is to trap and remove them.
“Directly addressing the threat of green crab requires both early detection and rapid response, with the goal of finding isolated populations when they are still rare and reducing or eliminating them,” said Allen Pleus, WDFW’s Aquatic Invasive Species Unit lead.
For more information about how to identify green crab and what to do if you find them, visit wsg.washington.edu/crabteam. If you do find a green crab, leave it in place, and take multiple photos to email to firstname.lastname@example.org for verification.