Green crab discoveries in Ketchikan show the invasive threat is spreading in Alaska

Thousands of the crabs have already been trapped in southern Southeast Alaska, and experts advise the public to be on the lookout for more that are likely to arrive

The European green crab, as pictured here, is an invasive species that threatens native fish populations. The invasive crabs were first discovered in Alaska in 2022 at Annette Island, and their numbers in the state have grown dramatically. In June, their shells were found in Ketchikan. (Emily Grason/Washington Sea Grant)

On a sandy beach in a state park in Ketchikan, a group of local beachcombers encountered something ominous: shells of two invasive European green crabs, shed as part of the creatures’ growth process.

That discovery, made during a June 6 beach survey that was part of a class held by the University of Alaska Southeast Ketchikan campus, led to more in the community.

It makes Ketchikan the newest known Alaska beachhead in a northward invasion of non-native crabs that are known to wreak havoc on native species and habitats.

European green crabs, first confirmed to be in Alaska when their shells were discovered in 2022 on Annette Island in the far southeast corner of the state, are likely here for good, said the UAS professor who was one of the class instructors and helped lead the beach surveys.

“They have continued to spread. They will continue to spread,” said Barbara Morgan, who is based in Ketchikan. “They are expected to spread through Southeast Alaska, probably most of Southcentral — kind of the southern coast of Southcentral. And maybe, depending on water temperature and how tolerant they are to the colder water temperatures, they might go up into the really southern part of the Bristol Bay area, too.”

In time, they could threaten some of Alaska’s most important habitats for salmon and other fish.

The crabs eat salmon fry, juvenile native crabs like Dungeness and other fish, and they mow down eelgrass beds that are important Alaska fish habitat.

“Green crab could potentially damage Alaska’s multi-billion dollar fisheries industries, especially for salmon, crab, and mariculture operations,” the National Oceanic and Atmospheric Administration has warned.

European green crabs were first found in waters of the U.S. East Coast in the 1800s, believed to have been transported in ships’ ballast water. In 1989, the first green crabs were discovered in U.S. West Coast waters, also believed to have been carried accidentally in ballast water. Over the following years, they spread northward. The first sightings in British Columbia were in 1998.

The Alaska first discovery, at Annette Island, was about 30 miles south of the beach site where Morgan’s class found the crab shells in June. And last summer, green crab shells were found at Gravina Island, just west of Ketchikan.

An eventual discovery in Ketchikan was largely expected. But the precise site of the June 6 discovery — at Refuge Cove State Recreation Site — was a bit surprising because of the nature of the site, Morgan said.

Green crabs generally prefer estuarine areas, places where freshwater and saltwater meet, and places with thick eelgrass, she said. But the Refuge Cove beach site is sandy and not an estuary, and thus not considered to be a prime spot for the crabs.

Crabs’ upper shells, called carapaces, are discarded periodically as the animals grow and need larger shells. Discovery of the molted shells suggests that the invasive crab were in the larval stage when they were pushed by currents north to Alaska, Morgan said.

After the first two shells were found during the class survey, the discoveries in the community “snowballed,” with additional shells found at Refuge Cove, plus more at other sites along the Ketchikan road system, she said. It is likely that there are more at other sites that are less accessible for surveys, she said.

How to respond?

The species’ name can be confusing because the crabs are not necessarily green, Morgan said. They can be brown or yellow or reddish, or a mixture of colors, she said. Meanwhile, some native crabs that do belong in Alaska are green, including kelp crabs, and should not be mistaken for the invaders, she said.

The “European” part of the name is not accurate, either, she said. “Yes, they came from Europe; they’re not in Europe anymore,” she said.

Morgan and other invasive species experts are trying to spread awareness — and the message about what the crabs look like. Telltale signs come from the shape of the shells, which have three bumps between the crabs’ eyes and five spikes on either side.

The Metlakatla Indian Community, a Tribal government on Annette Island, has been particularly active in combatting European green crabs.

The Tribe established a detection program in 2020 and made the first discovery of shells in 2022, as well as the Gravina Island discoveries last year.

Through its program, the Tribe has also trapped thousands of European green crabs. The total had reached about 3,000 as of last summer, according to the Department of Fish and Game, and it continues to grow.

In just the past month, the Tribal team trapped over 300 of the live crabs on Gravina Island, said Ian Hudson, a fisheries biologist who coordinates the Tribe’s European green crab program.

“This year there has been an explosion in numbers, and we’re not at all surprised that Ketchikan is finding carapace,” he said by email.

Metlakatla’s efforts are highlighted in the Alaska Department of Fish and Game’s 2023-2028 plan for combatting European green crabs. That plan lays out steps for prevention, early detection, rapid response and control.

But by now, full prevention may not be possible anymore, Morgan said.

With millions of European green crabs on the West Coast, and with currents that continue t send their larvae north, it is highly unlikely that all incursions could be prevented, she said.

“Even if we get rid of all of them in Alaska, we would need to build a fence across Dixon Entrance, a fine net. And that’s obviously not going to happen,” she said, referring to the maritime border site between Canada and Alaska.

Instead, she said, “functional eradication” like what the Metlakatla Indian Tribe is doing with trapping is likely to be increasingly important, with focuses on key sites important to native species like salmon and Dungeness crab. Baseline surveys can help identify those areas that need to be most protected, she said.

Part of a wider invasive threat

While the European green crab is considered to be among the world’s most damaging invasive species, it is not the only one that threatens Alaska’s environment and fishing industry.

Another example is elodea, a freshwater plant often used in aquariums. First found in Eyak Lake in Cordova in 1982, it has spread to other lakes and streams in Southcentral and Interior Alaska. Potential economic losses — to commercial sockeye salmon and to recreational floatplane pilots — could be well over $1 billion, Tobias Schwoerer, a University of Alaska Fairbanks economist, estimated in a 2017 study.

Invasive northern pike in Southcentral Alaska, which have proved to be persistent, also pose ecological and economic threats. The fish prey on salmon, trout and other native species. The Department of Fish and Game has a program to remove invasive pike and try to limit their spread.

For now, much of the work to combat nonnative species is coordinated by the Alaska Invasive Species Partnership, a coalition of government agencies, university experts, nonprofits and community organizations.

The partnership has advocated for years for the establishment of a more robust organization within state government, an invasive species council, to organize wider protection and rapid response, if needed.

Bills pending in the Alaska Legislature would do that. One measure, House Bill 191, made it through one committee. A Senate version, Senate Bill 174, has not had a hearing, however.

In past years, similar bills progressed through the Legislature but failed to make it to final passage. The most recent was in 2022, when a bill to establish a state invasive species council passed the House by 33-2 margin but failed to reach the Senate floor before that session’s adjournment.

Proponents hope results in the coming session will be more successful.

The sponsor of the current House bill, Rep. Rebecca Himschoot, I-Sitka, worries not only about green crabs moving their way through Southeast Alaska but also invasive plants like knotweed that have appeared in important community spots like Harbor Mountain.

“Each year, there’s more knotweed and less salmonberries,” she said in an interview late in the session. She hopes the bill will win final passage next year, she said.

Sen. Forrest Dunbar, D-Anchorage, is another proponent of an invasive species council.

He said he has been aware of invasive species since his childhood in Cordova, where he and a friend earned money from a neighbor by killing invasive black slugs at about a nickel apiece. Later, as a member of the Anchorage Assembly, he worked on efforts to remove invasive chokecherry trees, which were introduced as ornamentals but have since crowded out native species along the city’s greenbelts.

Dunbar acknowledged concerns that an invasive species council would cost the state money because it would require a dedicated employee in the Department of Fish and Game. But he argues that failing to set up such a council would cause more expense in the long run.

“I would say, we can’t afford to not prevent invasive species from entering Alaska,” Dunbar said in an interview near the end of this year’s session. “It is very expensive to have invasive species to start pushing out native species.”

• 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. Alaska Beacon is part of States Newsroom, the nation’s largest state-focused nonprofit news organization.