Finding European Green Crab in Kasaan: What We Learned from a Trapping Event at Longhouse Beach
In early September 2025, Tribes, state and federal agencies collaborated to look for one of the world’s most notorious invasive species: the European green crab. What they found confirmed what many in Southeast Alaska have been worried about.
European green crab (Carcinus maenas) are considered one of the 100 worst invasive species globally. They’re aggressive predators that can dramatically alter nearshore ecosystems, threatening native crabs, shellfish, and other species that are culturally, nutritionally, and economically important to coastal communities.
In 2022, the first European European green crab in Alaska was documented by the Metlakatla Indian Community in Tamgas Harbor. Since then, the question has been not if they would spread, but how far and how fast.
This became especially urgent for communities on Prince of Wales in June 2025, when a green crab carapace was discovered during a crab bio-blitz on the island near Kasaan.
A Collaborative Effort on Longhouse Beach
From September 2–4, 2025, the Alaska Department of Fish & Game (ADF&G), Organized Village of Kasaan (OVK), Hydaburg Cooperative Association (HCA), and the U.S. Forest Service (USFS) teamed up to conduct a trapping survey on Longhouse Beach, an area known for its rich intertidal habitat and cultural importance to OVK.
Longhouse Beach was selected after molt walks revealed more European green crab carapaces there than at nearby Kasaan Harbor Beach. The area’s mix of sandy substrate, freshwater channels, logs, and rocks also makes it ideal European green crab habitat.
Although tides and daylight hours weren’t perfect, the team deployed an impressive 84 Fukui traps and 12 minnow traps, fishing them over three days.
KPUTv was on site as well, documenting the work and capturing footage of the collaborative effort.
What the Traps Revealed
The results were striking.
Over the course of the survey, 33 live European green crabs were captured at Longhouse Beach, confirming an established presence in the area. Approximately two thirds were male, and none appeared to be gravid, and their average size suggests they likely recruited in 2024.
European green crabs were most commonly found:
- In freshwater channels
- Over fine sand to small pebble substrates
- Near structural cover like logs, rocks, or erosion berms
One freshwater channel in particular stood out as a hotspot, likely because its shape and structure helped retain crabs during tidal movement. No European green crabs were captured in minnow traps.
Native Species Still Abundant
The traps also caught a wide range of native species, including:
Red rock crab (153)
Dungeness crab (49)
Hermit crabs (both grainy and hairy)
Shore crabs and sculpin
Interestingly, red rock crabs tended to occupy very different habitat than European green crabs, favoring large rocks and bedrock. Dungeness crab, however, overlapped more closely with European green crab habitat,raising concerns about future competition and predation.
Molt Walks Tell a Similar Story
In addition to trapping, teams conducted molt walks along the wrack line, collecting crab carapaces that were at least 50% intact. These surveys found at least 10 European green crab carapaces, along with molts from several native species.
Together, the trapping and carapace surveys paint a clear picture: European green crabs are present, active, and using prime nearshore habitat in Kasaan Bay.
What Comes Next?
The discovery of live European green crabs at Longhouse Beach is alarming, but it also provides valuable information that can guide next steps.
Future efforts will likely focus on:
Expanded monitoring across Prince of Wales Island
Later-season bio-blitzes (August–October) when detection may be higher
Targeted surveys in high-risk areas like Salt Chuck, a nearby estuarine system with ideal European green crab habitat
Building local trapping capacity, including encouraging residents and lodges to participate
Maintaining a ready cache of traps on POW for rapid response
Environmental DNA (eDNA) and tissue samples collected during the event will also help scientists better understand European green crab genetics and spread patterns as funding allows.
Community Science and Stewardship
This trapping event highlights the power of collaboration. Tribes, agencies, and local partners worked together to respond quickly to an early warning sign, demonstrating what community-based monitoring can accomplish.
European green crabs may be here, but so is a strong network of people committed to protecting Southeast Alaska’s nearshore ecosystems.
📺 Want to see the work in action?
KPUTv produced a video documenting the Kasaan trapping event. The video, In the Spotlight: European Green Crab, is available on the KPUTv app (account required; free to sign up).