Chinese mitten crabs, also known as Chinese hairy crabs, are considered a delicacy on Chinese dining tables. However, in the United States, these crabs are classified as invasive species. At the end of April, commercial fishermen captured a large male Chinese mitten crab in the lower Columbia River in Oregon, sparking high alert among biologists.
This marks the first discovery of Chinese mitten crabs (Eriocheir sinensis) in the Pacific Northwest of the United States, raising concerns about the spread of this highly invasive species.
According to the warning issued by the Oregon Department of Fish and Wildlife, a commercial fisherman captured this large male Chinese mitten crab at the lower Columbia River on the border of Oregon and Washington on April 22.
After accidentally catching the crab, the fisherman brought it to the Oregon Department of Fish and Wildlife, where a mollusk biologist confirmed it as a Chinese mitten crab.
Chinese mitten crabs have some unique features, including hairy, glove-like claws. These crabs have four spines on each side of their shell and a notch between their eyes. Their colors vary but typically range from brown-orange to green-brown. Despite their distinctive appearance, Chinese mitten crabs are difficult to identify and can easily be mistaken for native crab species and vice versa.
It is well-known that these crabs prey on a variety of organisms, including fish eggs, small invertebrates, and aquatic plants. Wildlife experts are particularly concerned about the potential impact of these crabs on the vital salmon population in the region.
Furthermore, a large population of these crabs can damage water infrastructure such as levees, dams, and breakwaters.
The Oregon Department of Fish and Wildlife stated that it is currently unclear how this crab entered the Columbia River – it could have been introduced by humans or inadvertently carried by past ships.
Chinese mitten crabs are a prohibited species in Oregon.
Biologists in Oregon are currently collaborating with counterparts in Washington and the National Oceanic and Atmospheric Administration (NOAA) to determine if there are other Chinese mitten crabs lurking in the river. They plan to set up trap lines and collect water and sediment samples to look for signs of the presence of these crabs.
While this is the first confirmed discovery of Chinese mitten crabs in the Pacific Northwest region, these crabs are not new to North America. They initially landed in the San Francisco Bay in California in the 1980s. By the late 1990s, fishermen there were catching between 100,000 and 800,000 crabs annually, according to data from the Smithsonian Environmental Research Center (SERC).
“Their numbers were astonishingly abundant. It was a real catastrophe,” said SERC biologist Greg Ruiz in 2018.
These crabs caused “serious infrastructural and ecological damage” in California, prompting officials from the Oregon Department of Fish and Wildlife to encourage the public to report any sightings.
Since 2010, Chinese mitten crabs have not been found in the San Francisco Bay, but they have appeared in other locations, including along the East Coast between Maryland and Connecticut. These crabs are occasionally found in the Gulf of Mexico and Great Lakes region, but they have not established breeding populations in those areas.
Chinese mitten crabs typically live in freshwater but must migrate to saltwater to reproduce. They are highly fecund, with adult females carrying between 250,000 to 1 million eggs. After hatching, the larvae spend a brief period in saltwater bays and estuaries. Once the juveniles mature and molt completely, they migrate upstream for several miles to reach freshwater areas.
Originating from East Asia, Chinese mitten crabs remain a popular delicacy in some regions. However, in the United States and the United Kingdom, these crabs are considered invasive species and are prohibited from being caught. In these countries, selling, exporting, importing, purchasing, and acquiring Chinese mitten crabs are all forbidden unless proper permits are obtained.
Anglers are not fond of these crabs as their sharp claws can damage fishing gear. Additionally, in some areas, these crafty crabs steal anglers’ bait and catches.
Controlling these crabs is no easy task. According to the U.S. Bureau of Reclamation, adult mitten crabs can survive for about a week in dry environments and over a month on moist grasslands. They can climb concrete structures up to 10 to 13 feet high and are known as “one of the strongest climbing species among crabs.”
(This article referenced a report from Smithsonian Magazine on May 2nd)