The study, led by researchers with the University of Maryland Center for Environmental Science, concludes that the oyster population in Maryland's portion of the bay has dwindled because of overfishing, habitat loss and disease to just 0.3 percent of what it was before intensive commercial harvesting began in the late 1800s. That's even lower than the estimate of 1 percent remaining that officials have been using for years.
"Habitat degradation and disease are a problem — it's just that fishing on top of that compounds the problem," said Michael Wilberg, a fisheries scientist with the Chesapeake Biological Laboratory in Solomons and lead author of the study. Funded largely by the state Department of Natural Resources, the research was published Wednesday in the journal Marine Ecology Progress Series.
Natural Resources Secretary John R. Griffin issued a statement saying state officials don't believe a moratorium is needed now, since the state has set aside 24 percent of the remaining oyster reefs in sanctuaries and beefed up penalties for poaching.
Larry Simns, president of the Maryland Watermen's Association, said he hadn't seen the study but added that the state's expansion of sanctuaries amounted to a de facto moratorium. Watermen contend that most of the best remaining reefs were put off limits.
At its peak, Maryland's oyster fishery was the largest in the world, yielding 15 million bushels a year. The catch had declined to about 1 million bushels a year by the mid-1980s, when a pair of parasitic diseases, MSX and Dermo, ravaged oyster beds and drove the harvest down even more. The harvest during the last oyster season, from Oct. 1 to March 31, was 121,173 bushels.
Since 1980 watermen have continued to take about 25 percent of the remaining oysters every year, the scientists estimate, a rate they say continued to reduce the population.
The harvest also reduced habitat for oysters, they note, since their shells provide the base upon which new oysters settle and grow. The study estimates that suitable reefs of oyster shells have declined by about 70 percent over the last three decades, partly because the reefs have silted over but also because harvesting has removed shells.
Besides their commercial value as food, oysters perform a vital ecological role in the bay, filtering the water and providing habitat for other fish. Maryland and Virginia have invested tens of millions of dollars in rebuilding oyster reefs and seeding the bay with baby bivalves spawned in hatcheries, but without seeing dramatic rebounds in the overall population.
Since Wilberg and his colleagues began their study, Maryland has overhauled its approach to managing oysters, expanding sanctuaries closed to commercial harvest while encouraging private aquaculture instead.
Wilberg called the state's policy shift "a step in the right direction," but said he doubts it's enough to produce a full recovery of oysters throughout the upper bay.
"I think it's a very good step forward, but I don't think it's enough to rebuild the population outside the areas where sanctuaries are present," he said.
Other scientists noted the study was the first to say that oysters have continued to be overfished in recent years. But they stopped short of endorsing its call for a moratorium, which could put hundreds of watermen out of work who still harvest oysters in fall and winter.
Kennedy Paynter, another University of Maryland oyster researcher, said the state's newly expanded sanctuaries are "essentially a partial moratorium" because they close off large areas of the bay and its rivers to harvest. If oysters rebound in those, he added, then perhaps more closures would be warranted.
Government and nonprofit groups already are spending millions seeding the bay with oysters produced in hatcheries and rehabilitating some old reefs. William Goldsborough, senior fisheries scientist for the Chesapeake Bay Foundation, said the success of small-scale oyster restoration efforts in Maryland and Virginia suggest a more gradual approach would yield results without needing a complete moratorium. Meanwhile, he added, the state's push to expand private oyster farming could offset the economic impact of a reduced public fishery.
Leaders of watermen's groups, who opposed the sanctuary expansion, contend that a baywide moratorium wouldn't help restore the oyster population. Left unworked, they argued, oyster bars would be buried under silt.
"Like a garden, you've got to turn the soil over if you want things to grow," said Jim Mullin, executive director of the Maryland Oystermen Association.
Simns of the watermen's association said he still believes the quickest way to restore the bay's oyster population would be to introduce disease-resistant bivalves from Asia. Maryland and Virginia decided against putting non-native oysters in the bay after an extensive study, concluding that they posed an undue risk of ecological harm.