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Data Collected will be Used to Guide Fishery Management Decisions
For the last century and a half, Chesapeake Bay oysters have yielded huge harvests and inspired debates, disputes and even open combat.
Yet during all that time, scientists and fishery managers never answered the most fundamental question about the Chesapeake's most iconic species: Just how many oysters dwell in what Native Americans called the Great Shellfish Bay?
Roger Mann, a longtime oyster researcher with the Virginia Institute of Marine Science, calls past efforts to assess the Baywide population "embarrassingly inadequate." "We spend a lot of time reading about their demise, and endless things are said - some misguided, some not - about potential restoration. Yet it is often done without any single, statistically accurate barometer of the numbers that are out there," he said.
Of all the major Chesapeake species, a Baywide stock assessment has never been done for oysters.
But the situation is about to change.
In the coming year, Mann and a team of scientists from universities and agencies in Maryland and Virginia hope to complete the first Baywide oyster stock assessment -- an overall population estimate and a clearer idea whether the bivalves are increasing, decreasing or holding their own.
The scientists hope to break down oyster populations in specific rivers and on specific oyster bars by age; determine their growth rates; assess the level of disease present; and discern whether it is fishing pressure or mortality from disease that most limits the population's increase.
This information is critical for fishery managers, who need it for informed decisions about harvest levels and restoration work.
"It may not be very sexy to do this sort of stuff, but it is very basic," Mann said. "And until you get an estimate of what is out there, and how it is changing over time, it is very difficult to make decisions about what's good and what works."
The assessment is being funded by the National Oceanic and Atmospheric Administration's Chesapeake Bay Office, which previously supported blue crab stock assessments that established similar much-needed baseline information and recently led to an overhaul of how that fishery is managed in the Chesapeake.
Oysters were so abundant when European settlers arrived that ships sometimes ran aground on oyster bars that towered far above the Bay floor. By the mid-1800s, the bivalves were supporting massive harvests that surpassed 20 million bushels a year as new technologies allowed Chesapeake oysters to be canned and shipped across the country.
But the resource has often divided Maryland and Virginia. Bitter disputes arose between the states over harvesting methods and they sometimes resulted in outright combat. Maryland even formed an "oyster navy" to enforce its laws and combat "oyster pirates".
The heavy harvests took a toll on the population and harvests declined in the 1900s. Shortly after the mid-century, two oyster diseases - MSX and Dermo - further hammered the bivalves, sending populations to all-time lows. Today, harvests peak at a few hundred thousand bushels, in good years.
Some estimates place the Baywide oyster population at 1 percent of historic levels, but generally stable. But a recent analysis by scientists at the University of Maryland Center for Environmental Science put the Maryland oyster population at 0.3 percent of historic levels, and continuing to decline - conclusions questioned by some other scientists.
The UMCES study recommended a moratorium on oyster harvests to help protect the population.
"There is a big dispute among researchers," said Mike Naylor, who heads the Maryland Department of Natural Resources' shellfish program, which is assisting with the assessment. "Some believe disease is the driver for oyster populations in the Bay, and others suggest that fishing-related mortality is more important. Hopefully, the new stock assessment will help inform that discussion."
The biggest obstacle to a solid, shared assessment is the differences in the way that the states collect data. They use different survey techniques to estimate population and record levels of disease in different ways. Even the bushel – a measure of volume -- is a different size.
Indeed, a Virginia oyster bushel is 3,003 cubic inches; a Maryland bushel is 2,800 cubic inches. And the two states use completely different methods to survey oysters and rank oyster disease. "It’s almost as if Maryland and Virginia didn’t agree, on principal, to anything," Mann said.
As a result, the scientists plan to develop ways to credibly compare information collected by such vastly different techniques, and modify future sampling to make comparisons more direct.
The assessment will also collect new information about the status of oyster shell around the Bay. Shells are a critical building block of oyster populations, but work in Virginia indicates that the amount of shell (and therefore potential oyster habitat) is steadily shrinking.
The scientists will also test new high-tech monitoring techniques, such as the side-scan sonar, which may allow future surveys to cover more ground at less cost.
Once techniques for comparing the states’ data are developed, scientists will be able to review records dating back for at least the past couple of decades and piece together a clearer picture of population trends by age, and the impact - if any - of fisheries on oyster stocks Baywide, in individual tributaries and even on individual oyster bars.
"If this study shows that fishing-related mortality is far more important than we realized, that argues for greatly restricting the fishing effort to allow populations to rebuild," Naylor said. "If the study suggests that it is true that disease-related mortality is the population driver, then making the fishery smaller wouldn't necessarily have any benefit. So I think this study has the potential to dramatically change the way that Maryland manages its fishery."
But, he said, it could show that the truth is more complicated - that in some places disease is most important in influencing populations, while harvest is most important in other areas.
The ultimate hope is that the Baywide oyster stock assessment effort will follow in the path set out by blue crabs. One to two decades ago, there were wildly different views about how - even whether - blue crabs should be managed. But NOAA began funding a Baywide winter dredge survey to help estimate the population.
The survey proved to be a remarkably accurate tool. A series of peer-reviewed stock assessments begun in the late 1990s used its data to provide increasingly precise estimates of the overall health of the crab population, ultimately showing that it was being overfished. That led to bi-state efforts to slash catches in recent years, an action that helped the stock rebuild from near-record lows.
Because NOAA has no management responsibility for oysters, officials hope the assessment will be viewed as unbiased, and build common ground around a species whose management remains so polarizing that some scientists and managers barely talk to one another.
"We are trying to be objective parties that can support such an assessment and provide it to the management community," said Peyton Robertson, director of NOAA's Bay Office. "It will hopefully be viewed as the reliable source of information on the status of oyster stocks in the Bay. Hopefully, that will provide a solid baseline from which to evaluate the protection and restoration efforts as we proceed."
Indeed, just knowing how many oysters are in the Bay would be a landmark step forward.
This article credits Bay Journal News Service
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