Fishery officials this fall issued the equivalent of an “all points bulletin” in their search for an unwanted alien. But they were pleased to not find their suspect—a foreign crab.
When a Chinese mitten crab turned up in a waterman’s crab pot this summer in the Patapsco River, fears were heightened that a breeding population of the exotic creature might become established in the Bay.
After the initial crab turned up, only one other find was confirmed—one that had been collected more than a year earlier and stored in a freezer. Several other sightings were reported, but not verified, leaving the status of the mitten crab uncertain.
In their native Asian habitats, the crabs migrate down rivers and into estuaries to spawn in the fall. So state and federal officials alerted almost everyone on the water to keep an eye out for the crabs: fish survey crews, stream monitors, watermen, oyster gardeners and others.
“It was an APB for everyone,” said Lynn Fegley, a fisheries biologist with the Maryland Department of Natural Resources.
The DNR even spent an entire day in mid-October drawing a 25-foot trawl around the area of the Patapsco River where the foreign crab was found. The bottom line: through mid-November, which covered the most likely migration period, no one saw anything, raising doubts that a population is breeding in the Chesapeake Bay.
“We dodged a bullet,” Fegley said. “At least we think we did, knock on wood.”
But, she cautioned, it’s hard to prove that something is not present. “It’s a big Bay,” Fegley said. “They could be there, but in very low numbers.”
And, while biologists ramped up efforts to look for the crab during the fall—when it makes spawning migrations in its home territory—Fegley noted that species sometimes change behavior when introduced to a new location.
The Chinese mitten crab, (Eriocheir sinensis), is a concern because it is a prolific invader, and females can produce between 250,000 and 1 million eggs each. Scientists at the Smithsonian Environmental Research Center’s Marine Invasions Research Lab consider the mitten crab as a “potentially harmful invasive species.”
On the U.S. West Coast, the crabs were discovered by shrimp trawlers in southern San Francisco Bay in 1992. Since then, they have spread rapidly in that bay and moved upstream.
A rapid expansion of mitten crabs in the Chesapeake, scientists say, has the potential to displace other species, and it is also a likely predator of some fish eggs.
One positive result from the discovery in the Bay this summer is that biologists now have a plan to deal with mitten crabs if they turn up again. A mapping system was developed to identify areas where mitten crabs were likely to be found, and an alert system was established to notify biologists, and the public, to look for and report crab sightings.
That’s important because, if the crab is not here now, they could be back. It’s thought the crabs likely arrived either in the ballast holds of cargo ships—which draw in water from one port, and release it at another—or were illegally imported because mitten crabs are considered a delicacy in some Asian communities.
“We have this infrastructure in place so if we do see them again, it will help us respond faster,” Fegley said.