As Oregonians anticipate the opening of native Dungeness crab season later this month, wildlife officials are concerned about potential infestations of a non-native, highly invasive crab species.
A second Chinese mitten crab was detected in mid-November in the Willamette River, south of Portland. That makes two captures of the prohibited crab species in a single year. The first Chinese mitten crab in Oregon was detected in April, in the lower Columbia River.
The Oregon Department of Fish and Wildlife, in partnership with the Oregon Invasive Species Council and Portland State University, has initiated a response plan to determine if a larger infestation exists.
Chinese mitten crabs are distinguished by their fuzzy, mitten-like claws and presence in fresh water, where they live as adults before migrating to brackish water to breed.
“Two detections in one year is really concerning for everyone at ODFW and our partners,” said Adam Baylor, ODFW Public Information Officer. "If somebody has dumped a crab and it's a one-off event, that's kind of what we can hope for. But, if it is an infestation and we're seeing other ones, we'll report that to the public with a follow-up."
Baylor referenced historical problems with Chinese mitten crabs in other regions, such as major colonizing in Europe and a significant, though ultimately resolved issue in California in the 1990s. He said the crustaceans’ destructive potential includes burrowing into dikes and stream beds, leading to erosion and flood risks.
“They can also wreak some havoc to the environment in terms of preying on native species,” he said. “They eat a lot of fish eggs, so you can imagine they would be out eating salmon eggs and steelhead eggs–competing with our native fish in that way.”
He said mitten crabs can also prey on native crayfish.
It is unlawful to possess Chinese mitten crabs in Oregon. Baylor suspects the crabs were likely introduced into waterways through illegal dumping.
“The most probable cause for their appearance was illegal release from the food trade,” Baylor said.
The ODFW is urging the public to report any suspected sightings of the Chinese mitten crab in Oregon waters. The agency says it’s important to correctly identify the species and report it to 1-866-INVADER, or report it online via the Oregon Invasive Species reporting hotline form.
Photographs can be submitted through the hotline and people are encouraged to do so, as crab identification can be difficult and native crabs have been misidentified as invasive.
"Oregon is worth protecting,” Baylor said. “And a really key part of keeping it protected (is) just knowing what invasive species are harmful and how you can help."
