The European shore crab, a small but dangerous invasive species, has recently found its way into the waters of Southeast Alaska. In response, Petersburg residents are stepping up their efforts to track down and control this unwelcome visitor.
On July 19, a group of 19 volunteers gathered on the shores of Mitkof Island for the European Green Crab Awareness Day. Their mission was to search Petersburg’s beaches and waterfronts for signs of the invasive species.
Brandon Thynes, director of the Petersburg Indian Association’s Indian Environmental General Assistance Program, expressed concern about the presence of shore crabs in Southeast waters.
“Now they are in the southeastern waters and we are concerned because they will displace our native crabs and destroy habitat,” Thynes explained.
He said the shore crabs pose a serious threat to the delicate marine ecosystems of southeast Alaska. They are known for destroying seagrass, a keystone species that provides shelter for invertebrates and young fish, as well as the spawning grounds used by many native species.
“They like to tear up seagrass and dig holes,” Thynes said. “They’re really aggressive, so they compete with young dungees and other smaller native species and may eventually take them over.”
European shore crabs have been documented in the United States since the early 1800s, but they were first discovered on the Pacific coast in 1989. Since that first sighting in San Francisco Bay, the crabs have been spreading north rapidly. The first Alaskan shore crabs were reported in the summer of 2022. During a coastal survey on Annette Island, three carapaces—hard shells left behind by crabs—were found by the Metlakatla Indian community. Within a month, they had documented 75 shore crabs, both living and dead. This year, the shells were found further north, near Ketchikan.
The Mitkof Island Awareness Day Moulting March commemorated the second anniversary of the discovery of shore crabs in Alaska. Volunteers split into four groups and combed the island’s beaches at Wilson Creek Camp, Crescent Beach, Greens Camp and Woodpecker Cove. March organizers Thynes and Sunny Rice, Sea Grant Alaska’s Marine Advisory Program agent, focused their search efforts on the southern half of the island.
“They lay their eggs in the current and then drift to another bay, and that’s how they move up the coast,” Thynes said.
Rice explained, “That’s why we chose the south end of the island because since they are south of us, the south end with the currents from Clarence Strait was the most likely. Woodpecker Cove campground was the best place to look. There were 31 Dungeness crabs, one Lyre crab and one shore crab.”
Although a total of 33 shells were found, none of them belonged to the European shore crab. While this is good news for the region, Rice pointed out that it is entirely possible that shore crabs have been in the area for years, but people are only now actively searching for them.
“We don’t know if they’ve been here a long time and people are just now finding out because we’re doing a lot more outreach … or if they’re moving,” Rice said. “But I don’t think we know for sure because we don’t have a lot of eyes on the ground.”
While the lack of confirmed sightings at the moment is a relief, it is also a reminder of how easily these crabs can slip through the net. While the organized molting migration only occurs once a year, Rice and Thynes conduct monthly live-catch surveys to monitor crab populations.
A week after the walk, Rice and Thynes were near Banana Point checking the traps they had set the day before. Rice described how difficult it was to find the right place to place the trap.
“They’re really specific,” she said. “So you could set a trap 200 yards away, and there’d be a whole bunch of green crabs over there. If you didn’t aim for them, you’d miss them.”
Although they have not yet found any shore crabs near Petersburg, Rice emphasized the importance of the research.
“The data from future surveys will be useful because they will give us a longer-term picture of the changes that might occur when they come. We can say, ‘What did this beach look like before they came, and how did it change when they came?'”
If you spot a crab that looks suspicious, experts like Thynes and Rice urge you to report it immediately. Thynes offered some tips for identifying a shore crab:
“To identify a green crab, they have five spots on either side and three spots in the middle between the eyes.”
“None of the other crabs will have that combination,” Rice added. “And it’s really jagged. I’ve told people it gets about the size of the back of your hand. It’s not huge, but I think it’s kind of this trapezoidal shape too.”
“They’re called green crabs, but they’re not always green,” Thynes added. “They can be orange, they can be reddish.”
If you see a crab that fits this description, take a photo and report it to the Alaska Department of Fish and Game or call the Invasive Species Hotline at 1-877-INVASIV (468-2748). The public is asked not to kill or capture the suspected crabs, as confusion may occur.
(Photo by Olivia Schmidt/KFSK)
