Non-native sea snail threatens bay life; Recently discovered pest eats shellfish


To the list of species that don't belong in Chesapeake Bay and probably will harm its delicate balance, add the veined rapa whelk, a snail with an appetite for shellfish that has been feasting on clams and oysters near Hampton Roads, Va.

Watermen working around the mouths of the James and York rivers say they've seen these creatures that vaguely resemble the native conch for several years, but only recently did they know what they were and how much damage they can cause.

"It's fewer clams now," says Billy Crew, a watermen from Gloucester Point, Va. "It's black and white. The year before last, we'd catch 2,000, 2,500 in a day. Now, we have to go like hell to catch 1,500."

Whelks are among a number of non-native species introduced to Chesapeake Bay by accident -- they came in on ships from international waters -- or for hunting and trapping or ornamental value. Often, the species edge out native species for food and habitat or cause environmental damage.

The water chestnuts that choked a tributary to the Bird River in May were brought to the United States as ornamental plants early in the century. Nutria, the large mammals that look like a cross between a beaver and rat and have been chewing through Eastern Shore marshes, were imported from South America for fur production in the 1940s.

Mute swans, with snowy white feathers and graceful necks, were imported to the Hudson River valley in the 19th century because of their beauty. Now, they are terrorizing native birds from the Chesapeake to Michigan and taking over their territory.

The whelks, Rapana venosa, have become such a concern that the Virginia Institute of Marine Science (VIMS) has put a bounty on them, offering watermen $2 a snail when they can produce 10 or more, or a T-shirt for every 10 whelks.

It isn't that they think bounty-hunting watermen will wipe out the species, says Roger Mann, the VIMS scientist studying the whelks, but it's a good way to get enough whelks to study.

"It makes them worthwhile for commercial fishermen to give them to us. It's how I can get the most information for a relatively small amount of money," he says.

Thus far, he says, he has collected more than 600 whelks.

Researchers believe the first whelks, which are native to the Sea of Japan, were expelled into bay waters from the ballast tanks of freighters coming into the port of Norfolk in a widely accepted maritime practice known as ballast exchange.

Commercial ships typically release the millions of gallons of water they carry for stability at or near ports and take on new water. As a result, they dump whatever sea life they picked up in their previous ports and gather more sea life to take on to the next port.

Rapa whelk, which are about the size of a fist but can grow to seven inches in length, probably have been in the bay "longer than people are aware of" because their larvae drop to the bottom and grow slowly. Some of them have reached maturity in the last year or so and have previously been too small to detect, says Kent Mountford, a senior scientist with the Environmental Protection Agency's Chesapeake Bay program.

Mann found his first whelk in August 1998. The others have been found between the mouths of the Rappahannock and James rivers and the Chesapeake Bay Bridge Tunnel, probably because they thrive in saltier water. Rapas can survive in full sea water, up to 31 parts per thousand, to about 20 parts per thousand.

Though salinity remains high in the main stem of the bay, it is not high enough in the Maryland part of the bay to support rapa, says Mann. "There's enough commercial activity in the upper part of the bay that if somebody had found one, somebody would've shouted, and shouted real loud."

Rapa whelk eat their prey by wrapping their bodies around clam or oyster shells, squeezing them open, then eating the meat inside. They prefer clams, followed by oysters and soft shell clams. A large rapa can go through three chowder clams in a week.

It is difficult, however, to gauge the economic impact on Virginia's seafood industry, because no one knows for sure how many whelks are beneath the waves.

"We've collected 600 or so of these animals," says Mann. "Now, if that's 90 percent of the population or more, then there's no problem. But if it's only 5 percent, then we have a serious problem."

The snail might have a commercial use, however. One of Mann's students brought a cook book back from Korea that contains conch recipes specializing in rapa whelk. And VIMS and the Virginia Sea Grant Marine Advisory Program are planning a seafood education seminar for Sept. 27 with rapa whelk on the menu.

"We do this a lot, where the great chefs from the local area come in and cook some seafood dish, and one of the local wineries brings its wines," says Mann. "This time, a chef from Norfolk is going to come over and cook rapa."

But what if rapa takes off, becomes commercially viable, is overfished and is then all but eliminated from Chesapeake waters?

"Everyone would be happy," says Mann.

Pub Date: 9/08/99

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