Endangered oysters Plague of parasites: Infection by lTC natural enemies may necessitate moratorium on harvest

September 24, 1995

IF THE WORLD is your oyster, pray that it's in better shape than those beleaguered bivalves of the Chesapeake Bay.

Just when watermen thought the worst had passed, and last season's harvest proved to be the best in three years, comes the news that two natural parasites have infected much of the bay's oyster population.

Maryland's hot, dry summer this year nurtured the resurgence of deadly microorganisms MSX and Dermo. Reduced freshwater flows in spring raised the salinity of the bay to near-record levels, promoting explosive growth of the parasites.

The extent of damage to oyster beds is still uncertain, as this harvest season begins Oct. 2. Watermen will be fortunate to match last season's yield of 165,000 bushels.

The lower bay is hardest hit, with half the population killed by fast-acting MSX, according to scientists. Virginia is ready to prolong last year's ban on oyster harvesting from public reefs. Maryland authorities have yet to act.

The widespread infection, which does not harm humans who eat oysters, is another serious blow to the bay's once healthy fishing industry. Emergency limits on crab fishing were imposed this month and the moratorium on catching rockfish was lifted only four years ago. Goose hunting is banned this season, as well.

Over-harvesting played a major role in each of those cases. The same has been true of oysters. Human activities have also caused siltation and destruction of oyster beds.

But the scourge of endemic parasites is a result of natural conditions. Years of research on disease-resistant varieties and of reseeding oyster bars have not been able to turn the tide. Aquaculture has yet to show promising results. Sadly, a harvest moratorium may be the only way to relieve human pressure on the threatened shellfish and provide some marginal hope for its recovery.

While the commercial importance of bay oysters has shrunk, as has domestic consumer demand, these creatures are essential in purifying polluted waters -- each filtering up to 50 gallons a day. That is an overwhelming argument for concerted protection of the bay oyster, even if it is no longer readily available on the half shell.

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