Metlakatla working to prevent spread of invasive green crabs
October 19, 2022
Natalie Bennett was walking surveying a beach on Annette Island as part of a team trying to defend Southeast Alaska from marine invaders when she made a major but ominous discovery: the state’s first documented shell of an invasive European green crab.
Bennett, a summer intern with the nonprofit Sealaska Heritage Institute who was working with the National Oceanic and Atmospheric Administration, noticed the tell-tale spines on the side of the eye areas. Right away, she notified one of her internship advisers, Barb Lake of NOAA Fisheries.
“I told her, ‘This is kind of concerning me,’” Bennett said. “I handed it to her, and she said, ‘No, it can’t be.’”
Bennett’s discovery on July 19 was the first step in confirming that European green crabs had spread farther north on the continent than ever been recorded before. They are small but highly aggressive crustaceans that are notorious for damaging native ecosystems.
Just two days later, the team found Alaska’s first dead European green crabs in the area. Live crabs were found in the days to follow.
That was not a surprise, said an official with the Metlakatla Indian Community, the island’s tribal government that, in partnership with NOAA Fisheries, is leading the green crab search.
“Once you find the shells, it’s not very long after that there are live crabs,” said Genelle Winter, a grant coordinator with the Metlakatla Indian Community.
Movement of European green crabs into the area was considered almost inevitable, but this summer’s discoveries were stunning, nonetheless.
“I just kind of figured eventually they would get up here. Be we all thought it would be a few years before they made it up here,” said Bennett, now back in her hometown of Juneau. “We just weren’t expecting them already.”
European green crabs — which, despite their name, can be red, yellow or mottled as well as green — are native to western Europe and northwestern Africa. They have been working their way westward since the early 1800s, when they were found on the U.S. East Coast, likely carried in ships’ ballast, according to NOAA.
The crabs made it to the West Coast by 1989, when they were discovered in San Francisco Bay. They have spread north since then, likely helped along with warming marine conditions resulting from climate change. In 2020, according to the Alaska Department of Fish and Game, green crab larvae were found in Prince Rupert, British Columbia, and the following summer, a population of adult green crabs was found on the province’s Haida Gwaii archipelago — dangerously close to Southeast Alaska.
The state Department of Fish and Game website lists a litany of negative impacts.
Besides cutting up eelgrass beds that are important for salmon and other fish, European green crabs gobble up clams, mussels, snails and other species; they have been known to wipe out entire mussel beds, according to Fish and Game. They also have the potential to displace crabs, including Dungeness, and they prey on oysters, which are important to the Alaska mariculture industry, Fish and Game warns.
People in Southeast Alaska were already worried about the green crabs prior to their discovery in the state, “because they’re super-invasive and really good at destroying ecosystems,” Bennett said. “They shred eelgrass. They just destroy everything.”
To look for the invaders, she drew on lessons from her youth, when she accompanied an uncle on his forays collecting crab carapaces for sculptures. She found the green crab carapace on the highest tide line — coincidentally, right below a sign that instructed people to be on the lookout for the invasive and destructive crabs.
The immediate focus is on plucking the crabs out of the water to prevent proliferation and spread. They are small, only about 2.5 to 4 inches across, and through some trial and error, Metlakatla residents and their partners have found that shrimp traps are the most effective tools for capturing green crabs.
Winter said there haven’t been any noticeable damage to fish populations. But there has been cut eelgrass, a typical result of European green crab presence, she said.
The effort to find and capture the invasive crabs will continue as long as the tribe has funding for it, Winter said. “This is not a one-and-done operation. This is something that’s going to require a sustained effort over a long period of time,” she said.
The European green crab search-and-destroy mission is part of a broader campaign throughout Alaska to prevent the arrival of invasive species or, if they are present, to remove them.