Much has changed since the Native Americans called the Chesapeake, “Tschiswapeki,” or “Great Shellfish Bay.”
Heavy fishing pressure and habitat destruction dating to the 1860s drove the population down through the 1900s. Only about a tenth of the Bay’s historic oyster grounds still provide suitable habitat.
Then, oyster diseases hammered the remaining population. By some estimates, the number of oysters in the Great Shellfish Bay is at an all-time low, as consecutive years of drought have allowed diseases to thrive.
To guide efforts to bring back the species, the Bay Program has drafted its first-ever Comprehensive Oyster Management Plan. The draft plan is the first time a single Baywide document was written to address both habitat restoration and fishery management issues facing the native oyster.
The draft plan, crafted during the past year by scientists from state and federal agencies, nonprofit organizations and universities, is expected to be available for a 30-day public review beginning Nov. 4.
The decline of the oyster is considered one of the most serious ecological — and economic — blows to the Bay. For many decades, the oyster was its most valuable commercial species.
In addition, it played crucial ecological roles: Oysters once helped to filter algae and sediment, clearing the water for underwater grasses. Their reefs provided important habitat for a variety of fish and other species.
“A restored oyster resource,” the draft plan states, “can be described as abundant, self-sustaining, occupying a major portion of their historic range throughout the Chesapeake Bay, providing important ecological services,and supporting an oyster fishery.”
The plan notes that attaining both ecological and socioeconomic goals will be difficult because they may be in opposition to one another, but said the oyster remains an important source of income for water-dependent families and communities.
No one knows how big the oyster population must be to achieve those objectives, the report said, but it calls the Chesapeake 2000 agreement commitment to achieve a tenfold increase in the oyster population as only “the first step” for oyster restoration.
To accomplish that goal, the strategy calls for establishing sanctuaries where harvests are off-limits; improving fishery management; and increasing hatchery production, particularly with disease-tolerant strains of the native species to rebuild the population.
The goal of the strategy is that, taken together, those three actions will offset the devastating impact of disease.
While some of those actions are either under way, or have been called for in other documents, this is the first time they have been woven together in a single, Baywide framework, with specific guidance to the states, to steer a restoration program expected to cost tens of millions of dollars over the next decade.
The plan cautions that because of disease and current environmental problems in the Bay, “progress toward increased oyster production may not occur in the short-term. The challenge is great, but the potential payoffs in both ecological and economic terms also are great.”
While the plan expresses optimism that headway can be made — even going beyond the tenfold oyster increase goal — it also says it is not possible to restore oyster populations to historic levels not only because of disease, but also because of drastic changes to the Bay ecosystem.
For example, the rapid increase in roads, parking lots, roofs and other impervious surfaces speeds runoff to rivers and the Bay. These surges of freshwater can reduce salinities in upper parts of the Bay and tributaries — where disease levels are lowest — to levels deadly for oysters.
A 1-inch rainfall in the upper Potomac today results in a freshwater surge equivalent to that of a 2-inch rainfall 30 years ago, the plan said. The result has been the loss of hundreds of acres of historic habitat in upstream areas.
Still, the biggest single obstacle to recovery is the challenge of increasing oyster survival in the presence of disease. Today, the vast majority of oysters die before they reach their full reproductive potential.
Under the plan, restoration activities will be tailored to three different salinity zones in the Bay, each with its own approach for dealing with disease.
Low-salinity zones have the least amount of disease and therefore the best survival, but usually have poor reproduction. Increasing populations in those areas will depend heavily on the use of hatchery-produced oysters, the plan said. It is this area where the increases in oyster populations would likely be seen first.
Medium-salinity zones are more likely to have better reproduction, but are also more susceptible to disease, especially in dry years when salinities increase. These areas have the potential for rapid population increases — and decreases — and will require managers to adjust their actions to take advantage of good conditions when they present themselves, perhaps by moving some small oysters to better areas.
High-salinity zones often have good reproduction, but because of constant disease pressure, few oysters survive. It’s unlikely that high-salinity areas will contribute to major population increases in the short term, the plan says, but any oysters that do survive are thought to have some tolerance to disease which may contribute to the long-term recovery of the population. The plan cautions that such a result would likely be “far beyond the timeframe of this initiative.”
The plan calls for using “adaptive management” for restoration in each zone. Essentially, different restoration techniques would be tested and re-evaluated in each zone to identify the actions most likely to achieve the goals.
The plan calls for establishing oyster sanctuaries in at least 10 percent of the historically productive oyster grounds throughout the Bay and its tributaries, and through each of the salinity zones. In the sanctuaries, harvests would be prevented and the states would maintain suitable substrates so oyster larvae — or spat — can settle.
The goal of sanctuaries in low-salinity areas is to increase population growth, survival and reproduction in the near future, whereas the goal of high-salinity areas is to produce disease-tolerant oysters over the long term by not harvesting the older oysters that survive the diseases and might pass those traits on to their offspring.
Efforts to improve habitat are needed inside and outside of the sanctuaries. Surveys indicate that about 90 percent of the 450,000 acres of historic oyster grounds in the Bay have been degraded, mainly as the result of being covered with sand or mud, which do not provide the solid substrate young oyster spat need to settle on and grow, the plan said.
Because there is only a limited amount of oyster shell available to place on the bottom to serve as habitat, managers have to choose their restoration sites carefully, the plan says. “The challenge for oyster restoration is to place clean shells in areas that effectively catch oyster larvae or place hatchery seed in these areas to facilitate oyster colonization. Areas will be successful only if oyster growth outpaces mortality and sedimentation.”
To achieve the tenfold population increase, the plan says new strategies to manage oyster harvests are needed. It said managers need to evaluate harvest levels to see if they are appropriate for restoration goals.
It calls for new approaches to management, such as establishing a system of open and closed harvest areas, where harvest activities would rotate over the years. The goal is to allow more oysters to reach 4 inches in size (the minimum harvest size is 3 inches) in the hope that they will not only be more valuable, but also allow some disease tolerance to develop that may be passed on to offspring.
In addition, harvest times may be more limited, but coincide with times such as Thanksgiving or Christmas, where there is more market demand, potentially increasing income for watermen.
Hatcheries, which have played important roles in rebuilding striped bass and shad populations around the Bay, may also play an important role in the return of oysters. The plan calls for the increased production of hatchery-reared oysters that can be used to stock areas that have little or no natural reproduction to help jump-start the population. Further, hatcheries can produce oysters from disease-resistant oyster strains, potentially increasing survival.
In addition, the plan says oyster aquaculture should be promoted because it would help boost overall oyster biomass in the Bay, as well as increase their economic and ecological value to the Bay.
The plan makes no recommendation about the use of nonnative oysters in aquaculture, some of which show more disease resistance than the native species, pending the outcome of a National Academy of Sciences review of the issue, expected to be complete next summer.
Copies of the plan will be available through the Bay Program’s web site, www.chesapeakebay.net