Volume 16, Number 1 • January-February 1998

Aquaculture and
Restoration

By Merrill Leffler

Not only is aquaculture bringing more farmed seafood to the table each year, it is also bringing assistance to resource and habitat restoration programs. In the Chesapeake Bay, for instance, hundreds of thousands of striped bass were released annually by public and private agencies - this was part of the successful program to restore the species throughout the East Coast. Populations of striped bass appear to be back to historical levels and agencies only have a limited need to release them now. Research and management agencies are currently looking at how aquaculture can help restore other species, among them, severely diminished shad populations and the nearly extinct sturgeon that used to roam the bottom waters of Chesapeake rivers.

But the greatest restoration challenge for aquaculture in the Chesapeake is its once-renowned oyster populations, which are at historical lows. The heavy loss of oysters to two parasitic diseases - Dermo (caused by Perkinsus marinus) and MSX (caused by Haplosporidium nelsoni) - has combined with a century of steady harvesting pressure and an increase in landborne pollution, especially sedimentation, to decimate the species.

Not only has the oyster industry suffered - watermen, suppliers, seafood processors and distributors - but so apparently has Bay water quality which depends, at least in part, on robust oyster populations and the communities that form around them. Only in recent years have we begun to appreciate how oysters and their habitats contribute to improving water quality by filtering algae, which remove some of the excess nutrients that are plaguing the Bay.

Despite their decline, oysters are resilient animals - this past summer, for example, the Chesapeake had a record spat set, new young oysters that settled on shells and other substrates throughout the Bay. Because of Dermo and MSX, however, most of these oysters are not likely to survive to harvestable size in the three years it generally takes oysters spawned in the wild. The poor prospect for survival is one reason restoration plans have been looking to the controlled spawning of oysters in hatcheries: hatchery operators can spawn oysters earlier than under natural conditions and give young oysters a big headstart in growing to maturity. Moreover, as specially-selected stocks are developed that are more resistant to disease, hatcheries can be used to get these oysters to growers for restoration purposes (see the January-February 1997 issue of Maryland Marine Notes). Such efforts are making it possible to better manage around disease by giving resource managers and commercial operations more flexibility.

For more than 20 years, Maryland Sea Grant Specialist and researcher Don Meritt of the University of Maryland Center for Environmental Science has been operating the hatchery at Horn Point Laboratory (HPL) and working with watermen to set their own oysters and plant them on privately-leased beds. With Dermo now entrenched on oyster beds throughout the Bay, Meritt has teamed with other researchers, including those at the Maryland Department of Natural Resources (DNR) and in the Maryland Oyster Recovery Partnership - a co-venture of watermen, aquaculturists and environmentalists - to spawn disease-free oysters in the hatchery and grow them to maturity in lower-salinity areas. While optimum growth in oysters favors higher salinities, disease pressure is generally less intense at lower salinities and the hope is that oysters can survive to maturity there.

The Partnership grew out of a unique consensus agreement in Maryland, says its executive director Robert Pfieffer, among watermen, aquaculturists, resource managers, legislators, scientists and environmentalists - its long-range goal is restoration of oyster populations. The agreement divided the Bay system into three zones, A, B and C. In the upriver and low salinity waters of Zone A, certified disease-free spat can be planted; furthermore oyster harvesting is not allowed in these areas.

Is it possible to bring these oysters to harvest before disease kills them? Further, asks Meritt, can we bring them to harvest under different climatic conditions, particularly when salinities are higher because of drought-like weather and disease intensity is therefore greater? So far the prospects are promising, says Pfieffer, though we need several more seasons of differing weather conditions to have a clearer idea.

In 1997, Meritt produced more than 20 million oyster spat at HPL - still only enough to plant some 20 to 30 acres of bottom ground. While DNR is also growing and planting disease-free seed, sustainable restoration could be lifetimes away. Consider that Maryland has some 270,000 acres of designated public oyster grounds (though most no longer produce harvestable oysters), says Meritt - our efforts are a measure of the task ahead of us.

Important inroads are being made in the effort to bring back the oyster in the Chesapeake Bay, but it will take more than aquaculture to restore what has taken a century to nearly destroy. It will take major efforts to maintain reductions of pollution from the land along with progress in ongoing research to develop oysters that are resistant to disease. But we have made a start, says Meritt. "They may be small steps, but at least they are steps."

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Aquaculture and Restoration

Aquaculture and
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