Metlakatla residents and partners trying to eject invasive crabs from their first Alaska beachhead

The first discovery of destructive European green crabs at Annette Island is spurring action to prevent damage to Southeast Alaska’s natural marine ecosystem

By: - September 8, 2022 5:00 am
The European green crab, as pictured here, is an invasive species that threatens native crf populations. European green crabs have been found as far north as British Columbia but have not yet been detected in Alaska. (Photo by Emily Grason/Washington Sea Grant)

The European green crab, as pictured here, is an invasive species that threatens native fish populations. In July, a Metlaktla Indian Community-NOAA Fisheries team found the first European green crabs ever documented in Alaska, with shells, dead crabs and live crabs at Annette Island in the state's far southeast corner. (Photo by Emily Grason/Washington Sea Grant)

When Natalie Bennett was walking surveying a beach on Annette Island as part of a team trying to defend Southeast Alaska from marine invaders, 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 July 19 discovery 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.

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.

Natalie Bennett, a Sealaska Heritage Institute intern working with NOAA Fisheries, holds the European green crab outer shell that she found on July 19 on the extreme high-tide line of an Annette Island beach -- right below a sign warning visitors about the destructive invaders. Bennett's discovery of the shell, called a carapace, was the first documented evidence of the invasive crabs in Alaska. After that first discovery, the Metlakatla Indian Community-NOAA Fisheries team found more carapaces, some dead crabs and dozens of live crabs. (Photo by Linda Shaw/NOAA Fisheries_
Natalie Bennett, a Sealaska Heritage Institute intern working with NOAA Fisheries, holds the European green crab outer shell that she found on July 19 on the extreme high-tide line of an Annette Island beach — right below a sign warning visitors about the destructive invaders. Bennett’s discovery of the shell, called a carapace, was the first documented evidence of the invasive crabs in Alaska. After that first discovery, the Metlakatla Indian Community-NOAA Fisheries team found more carapaces, some dead crabs and dozens of live crabs. (Photo by Linda Shaw/NOAA Fisheries_

“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.

And as of Sept. 6, the tally was 94 live crabs, eight dead crabs and 21 carapaces or hard upper shells, Winter said.

Annette Island, on which the town of Metlakatla is located, is at the far southeastern corner of Alaska. 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 onthe 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.

Barb Lake of NOAA Fisheries and two other team member work on July 21 setting traps in the Tamgas Harbor area to snare invasive European green crabs. (Photo by Linda Shaw/NOAA Fisheries)
Barb Lake of NOAA Fisheries and two other team member work on July 21 setting traps in the Tamgas Harbor area to snare invasive European green crabs. (Photo by Linda Shaw/NOAA Fisheries)

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 native 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 native 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.

Now that residents of Metlakatla and their partners have found the crabs, what will they do?

“That’s a fantastic question. It’s one we’ve been asking ourselves ever since it happened,” Winter said.

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.

Tamgas Harbor is located on the southern side of Annette Island, one of the most southeastern points of Alaska. As of early September, discoveries of live invasive European green crabs have been limited to the Tamgas Harbor area. (Photo by Barb Lake/NOAA Fisheries)
Tamgas Harbor is located on the southern side of Annette Island, one of the most southeastern points of Alaska. As of early September, discoveries of live invasive European green crabs have been limited to the Tamgas Harbor area. (Photo by Barb Lake/NOAA Fisheries)

Those they have collected are being stored in a freezer, with some samples sent out for DNA analysis, Winter said.

So far, the live crabs have been found only around a spot called Tamgas Harbor, though carapaces and carcasses have been found elsewhere, she said.

And so far, Winter said, there haven’t been any noticeable effect on 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.

Beyond Southeast Alaska, a particularly troublesome invasive species that have become established in the Southcentral and Interior regions is elodea, a fast-growing freshwater weed that can damage salmon spawning habitat and pose safety dangers to floatplanes. Another invasive species in Southcentral is northern pike, a fish that has been improperly transported from its natural range farther north and has fed on native fish in Southcentral lakes. Agencies and organizations are also on the lookout for zebra mussels, creatures that can attach to boats and be carried to new environments. In May, a boat being pulled northward by land was inspected at the Alaska-Canada border and found to have zebra mussels attached, albeit dead. It was decontaminated before being allowed to proceed to Alaska, according to the U.S. Fish and Wildlife Service, which staffs the border with agents to monitor such incidents.

As for Bennett, she is headed to the University of Alaska Southeast in the spring and is considering further studies in marine biology. She also remains curious about the European green crabs’ movement into Alaska. “I wish I were still in the internship so I could know how many more crabs they caught,” she said.

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Yereth Rosen
Yereth Rosen

Yereth Rosen came to Alaska in 1987 to work for the Anchorage Times. She has been reporting on Alaska news ever since, covering stories ranging from oil spills to sled-dog races. She has reported for Reuters, for the Alaska Dispatch News, for Arctic Today and for other organizations. She covers environmental issues, energy, climate change, natural resources, economic and business news, health, science and Arctic concerns -- subjects with a lot of overlap. In her free time, she likes to ski and watch her son's hockey games.

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