Wildlife officials in the United States have issued a fresh alert after a highly invasive crab species, native to China and South Korea, was discovered in Oregon for a second time. The Chinese mitten crab, notorious for its ability to climb vertical walls, poses a significant threat to local ecosystems.
Discovery and Identification
According to a news release from the Oregon Department of Fish & Wildlife (ODFW), the crab was found alive in the Willamette River on November 17. This sighting marks the state's second official record of the species, following an initial discovery in April roughly 150 miles away along the same waterway. The crab was collected by hand from shallow water and was not returned to the river.
The Chinese mitten crab is easily identified by its long legs, medium build, and most notably, its distinctive hair-covered claws. It measures about three inches wide and is typically brownish-orange or greenish-brown, with a notch between the eyes. A key distinguishing feature is the four spines along each side of its top shell.
A Formidable and Destructive Invader
The alarm caused by this discovery is compounded by the crab's remarkable physical abilities. As noted by the US Bureau of Reclamation, the species can scale walls as high as 13 feet. In one documented incident, several specimens escaped from a concrete holding tank with walls measuring a staggering 18 feet high.
Beyond its climbing prowess, the crab's behaviour is deeply damaging. It preys on native wildlife, consumes fish eggs, and competes aggressively for food, which can harm local fish populations and destabilise entire ecosystems. Furthermore, the crabs burrow into dikes, levees, and stream banks, increasing erosion risks and potentially compromising flood control and water supply infrastructure.
Origin, Spread, and Public Appeal
Native to the coastal rivers of the Yellow Sea, the Chinese mitten crab is believed to enter the country through illegal food trade channels, despite being unlawful to possess or sell in Oregon and several other states. They are often released alive into waterways.
The species has a history as an invasive pest, having established a population in California's San Francisco Bay Area by the 1980s and appearing on the US East Coast from 2005. Recent sightings have also occurred in New York's Hudson River and Long Island Sound.
ODFW biologists are now collaborating with the US Fish and Wildlife Service, Portland State's Center for Lakes and Reservoirs, and the Oregon Invasive Species Council to assess the extent of the invasion. The department has launched monitoring programs and is urgently asking the public for help.
Officials urge anyone who spots a suspected mitten crab to photograph it and report the sighting immediately to the Oregon Invasive Species hotline at 1-866-INVADER or via their online form. They caution that identification can be tricky, as the native hairy shore crab also has patches of hair on its claws. Crucially, the public is warned never to return a captured mitten crab to the water alive.
