PORTSMOUTH – New Hampshire fishermen are being asked to look out for an invasive Asian crustacean with white-tipped hairy claws. Researchers fear the Chinese mitten crab could colonize local waters and wreak ecological havoc.

The New Hampshire Estuaries Project wants lobstermen especially to help stop the hand-sized crab before it causes problems for them as well as salt- and freshwater ecosystems, as it has on the West Coast.

The invasive crab is a delicacy in China. But in the late 1980s, it hitched a ride to California and multiplied, according to Dave Kellam, project coordinator for the New Hampshire Estuaries Project.

"No one is sure how it got there. But in San Francisco, 10 years after it was introduced, they counted 750,000 crabs at one fish ladder," Kellam said. "I've seen a video of it. It's like a horror show -- piles and piles of crabs, making it difficult for fish to move through."

"The real stinker is they live in both fresh and salt water," said Kellam. "No native crab does that. So it messes up two systems, outcompetes creatures for food, and burrows into fresh water streambanks, causing big stream erosion problems. It's terrible." The crab has made forays in Europe, posing a threat to fresh and saltwater habitats. "Germany's been dealing with them since the 1930s," said Kellam.

So far, 13 of the prolific critters have been discovered on the East Coast in the last three years, most recently in the Hudson River in January. "It's not here yet. So this is all a nip-it-in-the-bud approach," Kellam said.

The New Hampshire Estuaries Project's anti-crab campaign is being launched from New York to Maine. On May 14, New Hampshire Sea Grant will hold a seminar for commercial fishermen at the Urban Forestry Center on the crab and a few invasive marine plant species.

"We're trying to be preventive, not reactive," said Ken Lavalley, Fisheries Scientist for Sea Grant and the University of New Hampshire. "We feel they may be on a northern migration, and we want this program in place so we can react."

If lobstermen see a crab with hairy claws that they've never seen before, they should hold onto it and call UNH Sea Grant at 749-1565.

Researchers will mobilize researchers to check whether the crab is in a place where it can be stopped from spreading, said Kellam.

"Once they start reproducing, the young travel with the current and spread where the currents go," Kellam said.