No invasive green crabs have been found outside the area on Annette Island where they were discovered last summer, though experts are working against a potential population explosion in Southeast Alaska.
Barb Lake, with the National Oceanic and Atmospheric Administration in Juneau, gave a presentation in Ketchikan last Friday about the invasive crab species that a team of scientists with the Metlakatla Indian Community first identified on Annette Island in July. It’s the only place that the crab has been captured in Alaska waters.
Lake said the green crab can change, degrade, displace, outcompete, destroy and possibly render native species extinct in their local environment.
The crab is a resilient generalist that can live in waters with low salinity, such as estuaries, or traverse areas with high salinity and will eat just about anything, including juvenile salmon, crab, clams, mussels and oysters, Lake said.
“They’re also able to filter feed when there is no food for them to forage, which is really impressive, and unfortunate for us, because no matter what’s happening in the environment, they can really adjust to anything.”
Lake said that this adaptive, predacious species has boomed on the coast of the Pacific Northwest in recent years.
“In 2021, more than 102,000 crabs were caught in the Puget Sound and along Washington’s coast, and this was an astronomical 5,500% increase from the 1,800 crabs they’d caught two years earlier in 2019,” Lake said. “When we say explode, that’s exactly the definition. They found them, and their numbers kept growing until they were out of control.”
On West Vancouver Island, 300,000 green crabs have been caught since November 2021. Unfortunately, she said, it looks like the crabs are moving in on Southeast Alaska.
“We knew they were on the way; we just hoped our waters were a little too cold and we’d be at the top of their range,” Lake said.
The crabs spread from Europe to North America in the 1800s by riding in the ballast water of cargo ships.
NOAA launched “early detection” efforts with the Metlakatla Indian Community in 2020, establishing a system of crab traps that would identify the first green invader. Then in the summer of 2022, Lake said, the community “discovered the very first evidence of the crabs by finding a carapace in some high intertidal grasses.”
Taylor Stumpf works for the Metlakatla Indian Community Department of Fish and Wildlife, and explained in an interview last Thursday that the team found its first live crab in July, inside of a traditional Tlingit salmon trap on a beach in Tamgas Harbor.
So far, the only live crabs found have been caught within Tamgas Harbor, a large bight on the southern end of Annette Island that is about five miles long and one mile across.
“It is a very popular site for people who subsistence crab and it’s also a very important site for subsistence shellfish,” Stumpf said. “People go down there all the time.”
Tamgas is full of eelgrass and seems to be a nursery habitat for young Dungeness crabs, Stumpf said.
Eelgrass is important habitat for native species as breeding and rearing grounds. During her presentation on Friday, Lake said that green crab “love to shred eelgrass.”
“It’s not because they’re eating it, it’s just a behavioral thing that they do. They will just go and mow it down, so they remove that fantastic habitat that the native species need.”
Stumpf acknowledged that the crabs threaten the local ecosystem, and could jeopardize traditional harvest opportunity for Metlakatla residents and stress commercial fisheries.
“As the species destroys eelgrass beds, they’re destroying essential habitat for juvenile fish such as salmon. This can ultimately devastate coastal ecosystem and it can really affect important commercial fishing and subsistence fishing resources in particular,” Stumpf said last Thursday.
According to Tammy Davis, the Alaska Department of Fish and Game invasive species program coordinator, a national park in Nova Scotia, Canada, discovered that green crabs had reduced eelgrass beds by 98%.
Stumpf said the community is doing everything possible to restrain the green crab population with the resources available. His team is “focused on eradication or functional eradication, trying to remove as many as possible.” He said there is no way to completely control or eradicate the invasive crabs at this time.
To date, Metlakatla’s Department of Fish and Wildlife crew has recovered 779 crabs from the reserve.
“We got a lot of shrimp pots, folding traps and also commercial-sized crab pots and we have placed about 100 of them, at times over 100, in the Tamgas Bay area, so we have a lot of traps out,” Stumpf said.
The team uses herring as the primary bait to trap the invasive crabs. Stumpf said his team is “resourceful” and also uses salmon carcasses that are being discarded by the Tamgas Creek Hatchery during the spawning season to lure in the invasive species.
“We have continued to look at other areas where green crab could be based on habitat suitability with characteristics like eelgrass, food sources and freshwater outlets,” Stumpf said. “We have found them nowhere else.”
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