The anticipated movement of invasive European green crab farther into Southeast Alaska was verified June 13 when 11 carapaces of the shellfish were collected on the shore of Gravina Island’s Bostwick Inlet, according to the Alaska Department of Fish and Game.
The inlet, less than 10 miles southwest of downtown Ketchikan, is a popular local spot for harvesting Dungeness crab.
The molted green crab carapaces were found by members of the Metlakatla Indian Community Department of Fish and Wildlife, and the Alaska Sea Grant program, who were conducting shoreline surveys under a state aquatic resources permit, according to a department announcement on June 14.
The discovery marked the first documented presence of the crabs outside of the Annette Island Reserve, where the crabs were first observed in Alaska waters on July 21, 2022.
Since then, the Metlakatla Indian Community has been conducting an intensive trapping effort for the crab, focused largely in the Tamgas Harbor area on the southern end of Annette Island, in an effort to reduce the invasive population. More than 3,000 European green crab, including gravid female crab carrying eggs, have been removed thus far, according to the June 14 announcement.
This past year, Emily Grason, a marine ecologist and crab team leader for Washington Sea Grant who was working with the Metlakatla Indian Community on trapping green crabs, said “catching gravid females is a relatively rare event” in baited traps. “Females tend to really hunker down and not necessarily take risks required to enter a trap,” she said. “It’s not impossible, it’s just rare, and what it tells us is that the population is fairly large.”
European green crab are “highly competitive, voracious competitors” that have destroyed commercial shellfish populations on the Atlantic Coast of North America, displaced native crabs and reduced eelgrass and other fish habitat in areas where they have become prevalent outside their native range.
“Unless controlled, they can significantly reduce biodiversity and abundance of inter- and subtidal species and cause damage to nearshore ecosystems,” said the June 14 announcement.
After first being observed in North America at Massachusetts in 1817, the European green crab eventually made its way to the West Coast, where it was first found in San Francisco Bay in 1989. By 1997, it was found on the Oregon coast, followed by Washington state in 1998 and in British Columbia in 1999.
That northward movement was not lost on Alaska researchers, who as early as 2010 were mentioning the potential arrival of the invasive crab in local waters.
“Unfortunately, Pacific Northwest states (as well as Atlantic Coast states) have been trying to find ways to eradicate (green crabs) for decades with no success,” the June 14 announcement said. “The best practice at this point has been to attempt to reduce impacts by intensive trapping called ‘functional eradication.’”
People who find the invasive crab are being encouraged to report the find to Fish and Game.
The Alaska Department of Fish and Game website has information regarding how to identify European green crab, which can be green, dark brown, yellow, white, red or mottled, and have five spines on either side of its eyes, and three rounded lobes between its eyes. The carapace width can be up to four inches across.
“If you find a crab or crab shell you suspect to be an EGC (European green crab), collect it and take it to your nearest ADF&G office or take photos of the crab or carapace next to a key, coin or credit card for a size reference,” the state announcement advised.
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