Mitten crab sightings in state on rise
They climb. They crawl. They are creatures of rivers and estuaries but can walk up to five miles on land.
In North America, they are anomalies. Not a single one of the continent’s native crab species evolved to live in freshwater, according to David Molnar, a senior marine biologist for the Connecticut Department of Energy & Environmental Protection’s fisheries division.
In other words, Chinese mitten crabs, which are native to east Asia and named for the dark fur that covers the adult males’ front pair of claws, should not be living in Connecticut.
But they are. Twenty-eight mitten crab sightings were reported statewide in 2021, according to a DEEP report, which shows only six were reported the previous year. While the number remains small compared to other regions combating the invaders, Molnar said, the state is asking the public to look out for the crustaceans, which could introduce new diseases and harm native fish species.
The earliest Connecticut sighting of a mitten crab occurred in Greenwich in 2012, and New Haven-area captures started to become more common in 2019, Molnar said.
While a large portion of the recent sightings occurred in the Housatonic River where it bisects Stratford and Milford, three mitten crabs turned up in Hamden last year, according to a DEEP invasive species map and the agency’s 2021 mitten crab report.
“It’s illegal to import them. I think most people don’t realize that. But if they do find them, contact me, contact us. Hang on to it — do not let it go,” Molnar said. “I will come pick up the crab.”
It’s a safe bet that a crab hanging out in a state river is a mitten crab, since Connecticut does not have native freshwater crab species.
If you spot one, the state asks you to email david.molnar@ct.gov or call 860-434-6043 to report the sighting, according to the DEEP’s website. Residents can also make a report online.
How they got here
Mitten crabs probably made their way to Connecticut through the food industry, Molnar said.
“We had a large bus ... not even six months ago where there were thousands of crabs smuggled in for food,” he said. “They’re a very popular food item in other parts of the world.”
While the bus was located in the Midwest, Molnar said, the crabs were for the New York market.
The DEEP report includes a photograph of another seizure. In the aerial shot, row after row of Chinese mitten crabs sit on a plastic tarp, stretching out before five people posing for the photo.
An array of packing materials and opened cardboard boxes sits on the nearby grass.
“U.S. Customs and Boarder Protection (CBP) seized 3,700 live Mitten Crabs from a load of T shirt boxes at the Port of Cincinnati,” the caption says. “Shipment originated in China and Hong Kong and were destined for businesses and homes in multiple states, mostly New York.”
The Cincinnati seizure occurred in 2020, according to Molnar.
“I’m sure in New York City people buy them, feed their families, and then they probably have too many and they release them not thinking what the damage is going to be,” Molnar said.
Concerns for Connecticut
Between January and April of 2021, commercial fishermen dredged up 11 Chinese mitten crabs in the Housatonic River in Stratford and Milford, according to the DEEP report, which lists as unknown the location of a twelfth crab found during that period.
Throughout the rest of the year, three crab sightings were reported in Hamden and seven turned up at the Mianus River fish ladder in Greenwich, the report said. Bridgeport, Derby, Milford and Westport each had a sighting, according to the report, which says two more Chinese mitten crabs were found in Stratford.
The presence of the mitten crabs raises concerns for native wildlife.
“They like to eat eggs,” said Molnar. “Any fish species that we’re trying to restore, they potentially could do damage there.”
And “because they’re from southeast Asia, they could introduce diseases that are not native to this area, and those diseases could become very abundant and injure various species of animals,” Molnar said. “You never know.”
Mitten crabs are excellent climbers and can stay out of the water for a long time, according to the biologist.
“They can go anywhere if they choose to,” he said.
While the crabs typically hibernate in mud during winter, “during warmer and wetter weather they have been documented traveling up to 5 miles on land,” he wrote in a follow-up email regarding the species.
Despite the species’ mobility and potential environmental impact, there is a bit of good news: Their numbers remain relatively low.
As compared with the 28 crabs sighted in Connecticut last year, thousands inhabit England’s Thames River, Molnar wrote.
And because New England does not provide a particularly welcoming habitat for the arthropods, he does expect they will become abundant.
“They haven’t moved east of New Haven at this state. I don’t think they’re going to become abundant because the habitat’s not ideal,” Molnar said. “Our estuaries, rivers and sound is much different than their habitat in southeast Asia.”