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Hairy-clawed invaders find way into N.J. bays
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A hairy-clawed Asian invader that arrived in the Delaware Bay two years ago has now been found in both the Raritan and Barnegat bays.
The Chinese mitten crab, also known as the Shanghai hairy crab, is hard to mistake - as people who have seen it can attest. The claws look kind of like mutton chops.
"Look for fur on the claws with two white tips sticking out," said Linda Barry, a biologist with the state Division of Fish and Wildlife.
The crab first arrived in the United States in 1993 in the San Francisco Bay. The first specimen on the East Coast showed up in the Chesapeake Bay in 2006, and a year later the crabs were found in the Delaware Bay and Hudson River.
Barry said only two specimens have been collected from Barnegat Bay, one near Toms River and one at Seaside Park, but they seem to be more prolific in the Raritan Bay.
"The Raritan Bay has quite a few, including females with eggs," Barry said.
The Delaware Bay specimens found in 2007 were all on the Delaware side of the bay. Barry said this year they arrived on the New Jersey side.
"This past May and June, some of our crab fishermen on the Jersey side have reported catching them in their crab pots," Barry said.
The division is asking crabbers to report any catches and to not return live crabs back to the water. In fact, biologists would love some samples. Crabbers who find one should freeze the specimen and call the state's Nacote Creek Marine Fisheries Office at 609-748-2020.
Barry said genetic testing is being done to try to determine the origin of the crabs. One theory is that they arrived in ballast water in a ship from Asia or Europe. While genetic testing may help determine the origin, each new report from a crabber helps the biologists learn more about distribution since they arrived.
There is concern about potential effects. Barry said the crabs can clog water intake lines and cause erosion of sod banks due to the deep burrow holes they dig. They have caused problems in other countries, including England and Germany, where they arrived to find a niche and no natural enemies.
There is also concern they could compete with native crabs - although they may not pose much threat to the most economically lucrative species in New Jersey, the blue crab, since mitten crabs live most of their life in fresh water. They do go to salt water to breed.
"It's too early to tell if they'll be a threat. They could all disappear. There are no new sightings in the Chesapeake since 2007, so they could have died off. It could be an intermittent type of thing," Barry said.
The Smithsonian Environmental Research Center, located in Maryland, is leading the investigation of the mitten crab invasion along the East Coast.
Genetic testing by SERC showed the specimens from the Chesapeake Bay came from Europe. The crabs arrived in Germany, likely in ballast water, in 1912 and then in England about 20 years later. They have since spread throughout Europe and caused a host of problems.
England once tried to reduce the numbers by calling on the public to eat them - mitten crabs are considered a delicacy in China.
As for the furry mittens, nobody has figured out what purpose the coarse hair serves. The scientific name of the species, Eriocheir sinensis, means "wool hand" in Greek.
Barry said the crabs move very quickly. Unlike some crabs, they don't swim, but simply walk on the bottom. Mitten crabs have been known to travel hundreds of miles in the water and even cross dry land to get from one body of water to another. Who knows? Maybe that's why they need the furry mittens.
E-mail Richard Degener:
How to help
Wildlife biologists are seeking data and frozen specimens. Report catches to the state at 609-748-2020. A Smithsonian Environmental Research Center poster about identifying mitten crabs is online with the story at PressofAtlanticCity.com
Posted in OCEAN on Wednesday, August 5, 2009 3:05 am Updated: 6:30 am.
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