Research group Washington Sea Grant announced Tuesday that the first detection of an invasive European green crab in the northern Whidbey basin was made in late September this year.
The northern Whidbey basin includes Skagit Bay.
European green crabs are a small shore crab known for damaging ecosystems, including in North America.
The species eats eelgrass, algae, baby clams, oysters and young native crabs, and when it digs up eelgrass, it destabilizes soil.
Although the species was first identified in the state in 1998, population numbers began to soar in 2021.
A volunteer with Molt Search, an early-detection program for the species, found a molt of a green crab at Similk Beach, on the Swinomish tribal reservation, this fall.
According to a Sea Grant news release, the group, Swinomish Indian Tribal Community biologists, and the state Department of Fish and Wildlife, then carried out a trapping effort in the area.
"We found a concerning number of European green crabs,” said Washington Sea Grant Crab Team Program Lead Emily Grason in the release.
The groups found 12 green crabs at three sites throughout Skagit Bay.
Due to the crabs' size, they had likely been in the area for "at least a couple of years," according to the release.
"SITC Fisheries Department staff knew that green crab would eventually reach our shores, but it was still disheartening to catch those first few crabs," said Talia Davis, Swinomish tribe fisheries technician, in the release.
Green crabs have largely increased in population this year in the state's inland waters after the climate pattern El Niño caused warm waters in 2024 that helped them to survive.
About 174,000 green crabs were removed statewide this spring and summer.
In about July, the Tulalip Tribes found the first detection of a green crab in the southern Whidbey basin, in Possession Sound, but did not find additional crabs.
Those involved with green crab efforts are asking that the public not kill or remove suspected green crabs, because the species is often not green in color. Native shore crabs can be misidentified by the public as green crabs.
The green crab is best identified by five spiny ridges on each side of its shell.
Those who believe they have found a green crab can report it with photos online to the state Department of Fish and Wildlife.
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