Chesapeake Oyster Diseases Make a Comeback

Bay Journal, Oyster rebound undercut by returning diseases, weak market

Oysters have been enjoying a run of good news lately, suggesting that the Chesapeake Bay’s keystone species is on the rebound after decades of decline and stagnation. There are a couple of clouds on the horizon, though, that could derail that upward trajectory.

In January, the Maryland Department of Natural Resources announced that its annual fall survey of oyster reefs found a bonanza of juvenile bivalves on the bottom of the Bay and its tributaries. The density of fingernail-size “spat” found in the dredged samples was the fifth highest in the last 39 years, DNR reported.

Not only that, but the survey crew found recently spawned oysters in places where they’ve been scarce for a long time, including the Potomac River and two of its tributaries: the Wicomico River and Breton Bay. The Patuxent and Tred Avon rivers also received what DNR called once-in-a-generation crops of juvenile oysters. The DNR crew found spat on 50 of 53 “key” reefs that are sampled every year around Maryland’s portion of the Bay — a breadth of distribution not achieved since 1985.

With 2023 marking the fourth consecutive year of above-median spat production, DNR called it a promising sign that the costly, long-running effort to restore the Bay’s historically depleted oyster population is finally bearing fruit. But most of the credit for the spat proliferation goes to the weather. The lack of rainfall in 2023 reduced the flow of freshwater from rivers into the Bay. That raised the Chesapeake’s salinity above average, providing an ideal condition for oyster reproduction.

As we often see, good news and bad news for the Bay often depends on the weather. But good news for oysters (dry years) is often bad news for Striped Bass.  

The state’s watermen have likewise enjoyed four straight years of increasing harvests. They landed more than 700,000 bushels in the 2022–23 season, the most in 36 years, with a dockside value of more than $30 million. As a point of reference, Maryland’s wild harvest bottomed out in 2004 at 26,000 bushels. That was largely the result of two oyster diseases that flared up in the 1980s and devastated the bivalve population until about a decade ago.

Those diseases, Dermo and MSX, have quieted down but linger in the Bay. They tend to revive when water salinity is elevated, as it was last year. For the first time in six years, DNR’s reef survey last fall detected above-average prevalence and intensity of Dermo. More than 60% of the oysters tested for the disease in a laboratory had it. The heaviest infections tended to be from the Choptank River south, tracking with increasing salinity down the Bay. DNR said in January that it was still checking oysters for MSX, but results from just eight sampled reefs showed an “alarmingly high prevalence” of it.

Neither disease can be passed to people, but both can kill an oyster before it grows to harvestable size, or even before it can spawn for the first time. DNR’s survey found more than half the oysters dead on one reef in the mouth of the Choptank, with mortality ranging from 21% to 50% down the Bay from there, although it was less severe in several of the tributaries.

Watermen say they’re seeing more “boxes” or dead oysters in their dredges and tongs, making it harder to harvest their limit. They’re also getting paid less this season than last, by at least $5 per bushel. And on top of that, there have been days when seafood dealers or oyster-shucking houses have declined to buy watermen’s catch at any price.

“In spite of modest numbers of oysters, we have next to no market and the prices [are] down from previous years,” said Ed Farley, captain of the oyster-dredging skipjack H.M. Krentz in a mid-February text. Calling it a crisis, he added that he and his crew “only worked one day a week for the previous two weeks.” That was also the case in the first week of January and for a period after Thanksgiving.

In the long run, oysters ought to evolve their way out of the disease problems, but the long run could be a very long time.  Of more interest to me is that despite relatively modest increases in harvests the price of oysters has lagged. 

Robert T. Brown Sr., president of the Maryland Watermen’s Association, said the supply of oysters is simply exceeding the demand, especially with food prices higher as a result of inflation. “Seafood is a luxury, not a necessity,” he said. “There’s a lot of people who just don’t have the money for it.”

Some think the problem runs deeper, reflecting long-term changes in public attitudes about cooking or eating oysters. Others blame competition from oysters harvested in the Gulf of Mexico for glutting the market and driving prices down.

Actually, said Matt Parker, an aquaculture business specialist with the University of Maryland, “Nobody really has a good understanding of the oyster market and what’s going on nationwide.”

Have people lost their taste for oysters, or this some residual effect of the pandemic? 

The Wombat has Rule 5 Sunday: Poolside open and ready for business.