More invasive crabs collected around Metlakatla; harmful to juvenile salmon

The total of invasive European green crabs found in the waters around Metlakatla has risen to 34 live ones, plus some dead ones and a dozen shells of the destructive species.

The latest count, from Aug. 9, follows the discovery in July of the first sightings ever in Alaska, according to the Metlakatla Indian Community Department of Fish and Wildlife, the state Department of Fish and Game and federal NOAA Fisheries.

The live crabs have been found in Tamgas Harbor, and the dead crabs in Smuggler Cove.

Green crab infestations are damaging in numerous ways, according to officials. They overtake and feed on beds of eelgrass — a common home to juvenile salmon and Dungeness crab — where they compete against native species for habitat and food. They are voracious predators that prey upon a variety of clams, mussels, oysters and small crustaceans — including small Dungeness and other crab species up to their own size — and even juvenile salmon.

Metlakatla had been conducting early detection monitoring operations for green crab in the surrounding waters of Annette Island for more than two years when the first specimens were discovered. Now that the invaders have entered Alaska waters, Dustin Winter, director of the community’s Department of Fish and Wildlife, said increased trapping efforts are the next course of action.

“What we’re going to try to do now is just continue this trapping program and expand it,” Winter said. “We're going to try to get more pots in the water and as we move forward in different locations, we'll really determine what the problem really looks like. Because right now it’s just isolated in these two areas that we know of,” he said.

Tammy Davis, the state’s invasive species program coordinator, said the Department of Fish and Game will concentrate its efforts on areas that exhibit potential habitat for European green crab and will be monitoring more general areas, as opposed to places in closest proximity to Annette Island.

“Proximity isn’t necessarily the highest priority,” Davis said. “It has more to do with habitat suitability and currents. The idea is that juvenile crab larvae move on ocean currents and whether they settle out and survive is dependent upon suitable habitat. That’s why the habitat structure is really more important.”

European green crabs are native to European and North African coasts as far east as the Baltic Sea and as far north as Iceland and central Norway. They first were observed in North America in Massachusetts about 200 years ago. They now can be found in a wide range on both the East and West Coasts of the U.S. and several Canadian provinces. They reached San Francisco Bay in 1989, the Oregon coast in 1997, Washington in 1998 and British Columbia in 1999.

The invasive crabs are listed on the Global Invasive Species Database’s list of the “100 World’s Worst Alien Invasive Alien Species,” and were credited by the University of Maine with destroying Maine’s softshell clam fishery within the past decade.

In 2021, the Lummi Indian Business Council in Washington state declared a disaster in response to the removal of over 70,000 crabs in a span of five months from the 750-acre Lummi Sea Pond in Whatcom County.

Washington Gov. Jay Inslee subsequently issued an emergency order to address the problem by adopting “emergency measures, as necessary, to effect the eradication of or to prevent the permanent establishment and expansion of the European green crab.”

According to Washington State Department of Fish and Wildlife Public Information Officer Chase Gunnell, more than 100,000 green crabs were removed from Washington waters in 2021.

“That’s a frightening number,” Gunnell said Aug. 17.

Gunnell said that eradication has been deemed impossible in Washington, but that population-control efforts are being aggressively pursued in areas where there are large infestations. Extensive monitoring is also being done in areas where there are small populations of green crab, or where officials think they could potentially show up next.

He added that in the early stages of an infestation, extensive monitoring of potential areas in which green crab could appear is crucial.

“It’s important to put resources into areas where the crabs are known to be and to remove them, but it’s also really important to have monitoring,” Gunnell said. “You can do rapid response and remove them before an infestation takes hold.”

Canada Department of Fisheries and Oceans research scientist Thomas Terriault said Alaska has an advantage compared to other places with green crab infestations because of how early the crabs have been detected.

“We didn’t have any control efforts in the late ‘90s and early 2000s,” Terriault said. “It wasn’t like we were necessarily prepared for this. The lesson is to be prepared to intervene early and often.”

NOAA wildlife biologist Linda Shaw said the crabs likely made their way to Southeast Alaska from British Columbia by way of warm water currents, although she can’t completely disregard other potential modes of transportation, such as ballast water of boats or fouled ship hulls.

Shaw said the impacts of green crab can be devastating to several species living in Southeast Alaska’s intertidal ecosystems.

“They apparently can also filter feed like a mussel,” Shaw said. “So if they eat out house and home of some place, they might still be able to keep going just by filter feeding. That's really disturbing because then you don’t have that sort of normal check. They could maybe just keep going on filter feeding or cannibalism.”

She said infestations in other areas often remained at low numbers for years before exploding into massive quantities.

Those who believe they’ve encountered an invasive green crab or crab shell should take plenty of photos of the crab or shell with a key or coin for scale and call the state’s invasive species hotline at 1-877-INVASIV.

European green crabs come in a handful of colors besides green, including red, orange and brown. The crabs can be identified easily by the five spines on either side of the upper part of their carapace, which can range in width from two to four inches.

 

Reader Comments(0)