DEEP seeks public’s help fighting off invasive crab
Native to Asia, it is showing up in the Housatonic River estuary
MILFORD — The state Department of Energy and Environmental Protection is calling on commercial fishermen, recreational anglers and the general public for help fighting off a crab invasion that could have significant long- term effects on water quality, marine life and infrastructure.
The mitten crab, native to Asia, has started showing up in the Housatonic River estuary between Milford and Stratford, according to an alert from DEEP issued earlier this month. The crabs, about the size of a human palm and resembling spiders, with dense patches of hair on their claws, are among the most destructive invasive species in the region, according to David Molnar, a DEEP senior marine biologist.
Molnar said the mitten crab poses an ecological threat because the crabs spend most of their lives in fresh water and their main food preference is fish eggs.
“This is a big problem because DEEP is trying to restore salmon, trout and sturgeon, which has become an endangered species,” Molnar said. “If they were feeding on those eggs, it would really bring those species to a demise.”
Part of a river restoration, Molnar said, is introducing trout to an ecosystem.
“When we introduce trout to a river, they suppressed all the, what we would call undesirable species of fish, and improve the water quality,” Molnar said. “If the mitten crab comes in there and feeds on the trout eggs and there are no longer any trout there, these undesirable fish can become abundant, and the water quality could deteriorate.”
In addition to their effect on the ecosystem, mitten crabs also can damage stream beds and infrastructure, said Dave Hudson, a research scientist at the Maritime Aquarium in Norwalk.
“It damages infrastructure because it burros into the stream banks and destabilizes them,” he said. “It’s ( so destructive) partially because it does so much damage to stream banks.”
Hudson said in Europe the mitten crab has done more than $ 100 million in damage along the Danube River because their burrowing has damaged pilings and destabilized dams.
Mitten crabs first appeared in Europe in the 1970s, and reached the West Coast of the United States in the early 1990s. In 2007 the first mitten crabs were captured in the Hudson River, and they began showing up in the Mianus River in Greenwich in 2012.
Molnar said mitten crabs spend the winter in the Housatonic River estuary, and commercial fishermen have begun finding them in their shellfish beds.
The crabs could be more widespread, Hudson said, but the extent of their range is unknown because the eastern parts of the state do not have the same level of commercial shellfishing activity.
“It doesn't mean they are not in the Connecticut River, and since we don’t have a large shellfish industry there, nobody is there in the wintertime when the crabs are available to check,” he said.
Mitten crabs are the only crab in North America that spends most of their lives in fresh water. The crabs, which are delicacies in parts of Asia, are also routinely smuggled into the country, Hudson said.
“It is seized fairly often by APHIS ( Animal and Plant Health Inspection Service), which is the USDA’s unit that looks for invasive species and animal trafficking,” he said. “When they seize them, it’s a pallet of live crabs, and that’s a problem because they can survive in fresh water.”
According to DEEP Marine Fisheries Mitten Crab Report, the U. S. Custom and Border Protection seized 3,700 live mitten crabs from a load of T- shirt boxes at the Port of Cincinnati in January. The shipment originated in Hong Kong and was destined for businesses and homes in multiple states, including New York.
Smuggling makes the fight against invasive species much more difficult, Molnar said.
“A big part of this is to educate people not to smuggle in these animals because there are severe and dire consequences,” he said.
Besides the ecological and infrastructure problems that mitten crabs can have, Molnar said they are known carriers of roundworm and tapeworm that can infect humans.
“When you bring in an animal from a different part of the world, you bring diseases with them,” he said.
Hudson said biologists rely on the public to be their eyes and ears.
“I’m really heartened by the fact that we have folks who are on the water and are reporting this. I want to continue to encourage folks to keep an eye out,” he said.
Anyone seeing a mitten crab should contact Molnar at 860- 434- 6043 or david. molnar@ ct. gov. And anyone who happens to catch one should freeze it or put it on ice. Do not put it back in the water, he said.
“They could destroy hundreds of years of conservation management so quickly,” he said.