Japanese oysters don't thrive in bay

NO GROWTH INDUSTRY FOR IMPORTS

October 24, 1993|By Timothy B. Wheeler | Timothy B. Wheeler,Staff Writer Staff writer Tom Horton contributed to this article.

There's no place like home, or so it seems when Pacific oysters try living in the Chesapeake Bay.

They resist disease but don't thrive in the estuary, which is warmer and less salty than the ocean.

The Japanese oysters simply refuse to grow.

The evidence comes from the lower bay, where the Virginia Institute of Marine Science (VIMS) is experimenting with them.

A batch placed at the mouth of the York River over the summer is warding off the parasites that ravage the bay's native shellfish.

But the growth problem throws cold water on the idea that transplanted Japanese oysters might be the saviors of the Chesapeake shellfish industry.

One ray of hope: Their ability to resist disease could provide clues to help bay scientists breed hardier native oysters.

Fewer than 10 percent of the 200 Japanese oysters put in the York River at Gloucester Point are infected with MSX, says Dr. Dennis L. Taylor, director of VIMS. By comparison, nearly all of the native oysters in a control group have acquired the mysterious parasite, which quickly kills them.

Results are preliminary, but none of the Japanese oysters has Dermo, the other parasite afflicting the bay's shellfish, Dr. Taylor says.

More than a century of overfishing, pollution and disease have decimated the bay's oyster population. Maryland and Virginia watermen, who harvested 1.4 million bushels of oysters in 1987, managed to find only 166,000 bushels last year. That record low harvest prompted Virginia to limit its season this year and Maryland to seek new ideas on restoring the population.

The Virginia experiment, due to continue through the fall, is being closely watched because the Japanese oyster, Crassostrea gigas, is "farmed" on the West Coast and around the world. The bay's native Eastern oysters are a separate species, Crassostrea virginica.

Before the York River experiment, the Japanese oysters were treated with a chemical to prevent them from reproducing and possibly affecting native shellfish.

If the import can fight off parasitic disease, scientists want to find out how so that they can try to introduce the trait in native oysters through genetic engineering, says Dr. Eugene M. Burreson of VIMS.

Some seafood packers and scientists contend that the only hope for restoring oysters to the bay lies in introducing a species or strain of shellfish. But Dr. Taylor says early results of the VIMS experiment "seem to indicate that gigas is not really going to do well in Chesapeake Bay."

The Japanese oysters have not grown since being placed in nylon sacks in a metal cage and suspended in the York River off the institute's pier in late June. Some also have died, for unexplained reasons.

Though there was speculation that Japanese oysters might thrive in the lower Chesapeake, Dr. Taylor says the bay may be too warm and not salty enough for them.

It provides ideal water conditions for Crassostrea virginica, which can grow and reproduce in salinities of five to 30 parts per thousand and in water temperatures from 68 to 75 degrees. But the bay is about five to eight degrees warmer on average than the Pacific Coast waters where gigas thrives, and the Chesapeake has a greater fluctuation in salinity.

Gigas' lack of growth in the York River is no surprise to some scientists in Maryland. Japanese oysters tested in a state Department of Natural Resources laboratory a few years ago all died.

The preliminary results of Virginia's field trial were welcomed by HTC some environmentalists, who worry that the shellfish industry might press for hasty and large-scale introduction of the Japanese oyster.

It "basically doesn't like Chesapeake Bay," says William J. Goldsborough, fisheries scientist for the Chesapeake Bay Foundation in Annapolis.

The oysters used by VIMS should have grown faster than normal, he adds, because none of their energy was being consumed by reproduction.

Other scientists say the jury is out on whether Japanese oysters or some other strain or species might thrive in the bay, and they say that neutered oysters do not necessarily grow faster than untreated ones.

Dr. Roger Mann, another VIMS scientist, says the experiment was designed to test disease resistance, not growth. In the laboratory, he says, gigas can grow to 3 inches in less than two years, a faster rate than normal for virginica.

And gigas is not the only option, considering the variety of the world's oyster population, says Dr. Roger I. E. Newell, a shellfish biologist at the University of Maryland's Horn Point Environmental Laboratory.

"There are umpteen other species [and strains] of oysters out there," he says. One in particular, found in warm waters off southern China, may be more suitable to the Chesapeake than gigas.

"What's important is there are species which are not succumbing to the diseases," Dr. Newell says.

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