A species of predacious and destructive invasive European green crab was recently discovered for the first time in Alaska in the waters of the Annette Island Reserve by the Metlakatla Indian Community Department of Fish and Wildlife.
According to an announcement by MIC DFW posted to the MIC Facebook page on July 21, the discovery of three carapaces (crab shells) found on the Annette Island Reserve on July 19 marked the first evidence of European green crab in Alaska waters.
A separate announcement by MIC DFW, NOAA Fisheries and the Alaska Department of Fish and Game posted on Aug. 5 to the MIC Facebook page stated that 29 live crabs and 12 crab shells had been found in Tamgas Harbor, while two dead crabs were discovered in Smuggler Cove since July 19. That number had risen to 34 live crabs as of Aug. 9 and is expected to increase further.
MIC DFW 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, according to the Aug. 5 announcement. Now that the invaders have entered Alaska waters, MIC DFW Director Dustin Winter 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."
“So moving forward, we're going to expand. We've got 12 different locations that we've mapped out so far and we're going to be putting anywhere from 10 to 15 traps [in] those 12 locations to just get a handle on what's going on around the island,” Winter continued. “But until we know that, we're just going to keep going and keep trapping.”
Efforts to trap and monitor European green crabs have been conducted by MIC DFW, NOAA and the Alaska Department of Fish and Game, and assisted by the U.S. Fish and Wildlife Service.
ADF&G Invasive Species Program Coordinator Tammy Davis said that Fish and Game will be concentrating 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. So 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 to the locations that we would survey [rather] than proximity.”
European green crab 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 in 1817. 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.
Today, invasive populations of European green crab also can be found along the coastlines of southeast South America, South Africa and eastern Australia. 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 beginning “implementation of emergency measures, as necessary, to effect the eradication of or to prevent the permanent establishment and expansion of the European green crab.”
The order pushed the Washington Department of Ecology and Department of Natural Resources to “identify European green crab management as a high priority on their respective state-owned aquatic lands and to facilitate implementing emergency measures.” Additionally, the order requested emergency funding from the state Legislature to combat the growing problem.
According to Washington State Department of Fish and Wildlife Public Information Officer Chase Gunnell, more than 100,000 green crab were removed from Washington waters in 2021.
“That's a frightening number,” Gunnell said in a Wednesday afternoon phone interview. “But it also represents a real escalation in our response where we have coordinated removal efforts that are ongoing as well as monitoring efforts to look out for other potential hotspots through the Department of Fish and Wildlife, other state and federal agencies, co-manager tribes, shellfish growers [and] university and research groups. We have a real team here in Washington now that is out there trying to monitor and detect these crabs and remove as many as possible where we find them.”
Gunnell said that eradication has been deemed impossible in Washington, but that population control efforts are still 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. “So 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. “So it wasn't like we were necessarily prepared for this. The lesson is to be prepared to intervene early and often. And there are other examples out there for invasions where the money that you spend now may seem like a lot, but if you factor in how long you might be mitigating the impacts of an invader longer term, that becomes substantial.”
The official DFO Canada website also calls eradication of European green crab “practically impossible” once they’ve established a population in an area.
Green crab infestations negatively impact biodiversity in numerous ways, according to multiple sources. They overtake and feed on beds of eelgrass — a common home to juvenile salmon and Dungeness crab — in which 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.
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.
“We think it's natural dispersion as opposed to in ballast water or hull fouling or something like that,” Shaw said. “We don't know exactly, but it's been natural dispersion where they've been steadily moving north. Probably with El Niño events or warmer temperatures helping them to move north. And it's probably larval dispersion. There was a larva [reported] in Prince Rupert a couple years ago and a carapace found on Haida Gwaii. They've been in British Columbia and Washington for decades now. So they're dispersing northward, and it's probably just that population moving along with changing temperatures and taking advantage of currents. But you can't rule out some other factors that may have played a part, like ballast water.”
Shaw said the impacts of green crab can be devastating to several species living in Southeast Alaska’s intertidal ecosystems, adding that they appear to have even developed ways to survive in an invaded ecosystem after they’ve wiped out its main resources.
“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. So 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, and so I think that's why you can get these really high numbers of them in an area. Obviously it's not a healthy ecosystem to have this one super abundant species living there.”
She added that it's unlikely people will begin to encounter green crab in “their everyday lives” in the immediate future, stating that infestations in other areas often remained at low numbers for years before exploding into massive quantities. Although the invasion might seem small at the moment, she said that it’s of paramount importance to get ahead of controlling their numbers before things get out of hand.
“I think that people being aware of them and looking out for them and reporting if they do see them is super important,” Shaw said. “Because catching them at that early stage before they've exploded is how we are able to respond effectively as opposed to just dealing with an overwhelming situation.”
Those who believe they’ve encountered an invasive green crab or crab shell outside of Annette Island waters should take plenty of photos of the crab or shell with a key or coin for scale and report the sighting to ADF&G at https://www.adfg.alaska.gov/index.cfm?adfg=invasive.report or by calling the invasive species hotline at 1-877-INVASIV. It is currently against state regulation to collect, possess or transport banned invasive species without a valid permit.
Green crab or crab shells found within the boundaries of the Annette Island Reserve should be collected and frozen before being delivered to the Metlakatla Department of Fish and Wildlife. Annette Island sightings can be reported to the MIC DFW over the phone at 907-886-FISH.
European green crabs come in a handful of colors besides green, including red, orange and brown, meaning that color alone is not a definitive identifying trait. 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. A comprehensive identification guide can be found at http://www.adfg.alaska.gov/index.cfm%3Fadfg%3Dinvasiveprofiles.europeangreencrab_characteristics.
According to the NOAA Fisheries webpage on European green crab, they can be found on rocky shores, cobble beaches, sandflats and tidal marshes. They also may be found in beds of eelgrass or other shoreline vegetation. Because of their tolerance for varying salinity levels, they also can be found upstream of river mouths in estuarine environments. NOAA encourages citizens to search for and identify green crab in their local areas. Anyone interested in assisting detection efforts can learn more about citizen-based invasive species monitoring at https://www.fisheries.noaa.gov/alaska/habitat-conservation/look-out-invasive-crab#citizen-based-invasive-species-monitoring.
Davis explained that state regulations are in place to prevent the possibility of moving the crabs from one body of water to another, and to also prevent the killing of other crab species due to cases of mistaken identity.
“There are a number of native crabs in the nearshore that are also green and could be misidentified, and they're trying to protect those species,” Davis said. “We have a proposal into the [Alaska] Board of Fish right now to amend the banned invasive species regulation, only insofar as it would allow people to collect a green crab or another banned invasive species for the purpose of transporting it to a Fish and Game office to identify and verify the species.”
Current population control efforts by MIC DFW, NOAA, ADF&G and the U.S. Fish and Wildlife Service have revolved around extensive trapping efforts in order to both gauge the extent of the population and remove as many individuals from the tidal and intertidal ecosystems as possible, according to multiple sources.
While eradicating European green crabs from the waters of Alaska might seem like a tall order, Shaw believes that it is possible to rid the state of the invaders, due to how early the fight has begun.
“I think that's a possibility because we're catching it early,” Shaw said. “We have everything we know from Washington and Oregon and British Columbia, we have that to learn from. And so we're already having discussions about this as to [whether we can] take the lessons learned and if not completely eradicate them, at least stave off an explosion like they've experienced in those other locations.”
*This article was originally published in the Ketchikan Daily News*
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