The five-year review of oyster management options appears to have massively underestimated the likelihood that sterilized foreign oysters used in aquaculture would lead to the accidental introduction of breeding populations into the Bay.

Last October, the Army Corps of Engineers and the states of Maryland and Virginia released a 1,500-page Environmental Impact Statement that analyzed the risks and benefits of various oyster management alternatives aimed at restoring the ecological and economic role of oysters in the Bay.

Among the options analyzed was the potential for using nonnative C. ariakensis oysters, which have shown resistance to diseases that plague the Bay's native C. virginica oysters. One alternative called for large-scale aquaculture using sterilized nonnative oysters.

The EIS said the risk "appears to be small" that the sterile oysters would lead to the accidental introduction of reproductive nonnative oysters in the Chesapeake.

But a Maryland oyster gardener who reviewed the 1,500-page document discovered huge math errors in the EIS which, when corrected, suggested that an introduction of the foreign species would be inevitable from the large-scale aquaculture option.

"It made enough of a difference that they ought to pull that alternative off the table as an option," said Joseph Rodgers, a retired test pilot who now works as an engineer and uses sophisticated mathematical models in his work.

Virginia officials working on the EIS sent Rodgers' figures to the Virginia Institute of Marine Science, where scientists largely confirmed his numbers.

The draft EIS outlined three main options. One used only native oysters for aquaculture and restoration; another used native oysters for restoration but would allow the use of sterile C. ariakensis oysters in aquaculture; and a third option would allow the introduction of breeding C. ariakensis oysters in the Chesapeake.

Allowing the use of triploid C. ariakensis oysters in aquaculture had been seen by some as a potential middle ground in the contentious debate over the use of nonnative oysters in the Bay.

Supporters of that option said it allowed the seafood industry to take advantage of the fast-growing oysters with a low risk of an accidental introduction of breeding oysters. Critics contended that, over time, that option would nonethless lead to an accidental introduction.

But Rodgers' revised calculations suggests there is no middle ground, and that an introduction would be inevitable, and likely soon. That would leave decision makers with a stark choice: Prohibit the use of nonnative oysters altogether, or allow an introduction. "So what the folks in charge have to do is step up to the plate and make the hard choice: Do we introduce the foreign oyster or not?" Rodgers said.

Sterile oysters have been used in aquaculture tests in Virginia for years with little problem. They are created by crossing normal "diploid" oysters that have two sets of chromosomes with oysters that have been chemically treated to have four sets of chromosomes. The resulting offspring are "triploids" with three sets of chromosomes, generally making them incapable of reproduction.

The technique is imperfect, though. A small number of oysters would be capable of reproduction, and even some of the triploid oysters could become capable of reproduction over time.

The EIS estimated that only 271 reproductive-capable C. ariakensis oysters would be produced Baywide over 10 years, making the likelihood that reproductive males and females would occur in close proximity fairly low.

Rodgers found a series of major and minor mathematical errors-one involved a miscalculation of six orders of magnitude. Using figures in the EIS, he showed that more than 1 million diploid oysters could be produced at a single aquaculture site in a single year, whereas the EIS had put the number at .023.

"It does produce quite different numbers if you correct the math," said Jack Travelstead, director of fisheries at the Virginia Marine Resources Commission. He sent Rodgers' figures to the Virginia Institute of Marine Science, which largely confirmed Rodgers' figures.

In its response to the VMRC's question, VIMS scientists stated that "the important point here," is that it affirms the institution's position that commercial scale aquaculture with triploid C. ariakensis oysters "should be viewed as eventually leading to a diploid introduction."

Travelstead said the figures would be corrected in the final EIS, which is expected to be released with a final recommended action in April.

But the impact of the revisions is less clear. The estimates of oysters produced come from a mathematical model that includes a host of assumptions about oyster reproduction and survival. Because of a lack of oyster information, some assumptions are based on sea urchin studies. It also assumes massively increasing aquaculture with triploid C. ariakensis oysters.

When the model was recalculated over a 10-year period with the revised figures, Travelstead said, it found that triploid oysters in aquaculture would lead to a greater nonnative oyster population in the Bay after a decade than a deliberate effort to introduce a wild, breeding population- an unlikely result in the real world.

"In the end, the model really didn't help us a whole lot, and then it becomes a policy call," Travelstead said.

Stan Allen, a scientist at VIMS who works with C. ariakensis and produces the triploid oysters, said there's no way of knowing what would actually happen without putting huge numbers of triploid oysters in the water.

"There are certain things that seem unrealistic about the model," he said. "On the other hand, what's the alternative? You have to have some frame of reference for this, and the model is the only frame of reference that we have."

He said there would be no way of getting better information without significantly more research to reduce uncertainty in the assumptions.

Mark Luckenbach, another VIMS scientist who works with C. ariakensis oysters, agreed that assumptions in the model were "pretty wild." But he said that all efforts to correct the figures point to a greater likelihood of an introduction than previously suggested.

Luckenbach said he believed the EIS also underestimated other ways that breeding nonnative oysters could be introduced, such as accidental releases from large, commercial scale hatcheries that would be needed to support aquaculture.

"I believe that no matter what the numbers turned out to be for rare diploids among the triploids in the field, I would be prepared to say if the private sector-or even academia-is handling large commercial-scale quantities year after year of diploid ariakensis, then it would be very difficult to avoid an introduction."

As a modeler, Rodgers acknowledged the large uncertainties about estimating the risk of introduction. But the significant result, he said, is that all attempts to correct the numbers show an increased risk that reproductive-capable oysters would emerge from the aquaculture sites than what the EIS presented for public comment. "It is pretty clear that if they are able to introduce triploid aquaculture on that scale, it will undoubtedly result in an introduction of the oyster to the Bay," he said.

Despite the error, Rodgers said he found the lengthy document to be a valuable reference. "It was interesting to me. I'm a hobby oyster gardener, so I was learning a lot reading through it," he said. "There is lots of detail stuff that I didn't know about oysters. it was quite enjoyable. I just ran into a couple of things that caught my eye."

C. ariakensis decision imminent

As the Bay Journal went to press, officials were nearing a decision about which oyster management option from the draft Environmental Impact Statement to recommend as a means to restore oyster populations, and the oyster industry.

It was unclear, whether the three parties involved-Maryland, Virginia and the Army Corps of Engineers-would agree on the same option. It was also uncertain whether the decision would be formally announced before the release of the final EIS in April. After a 30-day comment period, a final "record of decision" would then be issued.

The three basic options include using only native oysters for restoration and aquaculture; using sterile nonnative oysters in aquaculture and native oysters in restoration; and using nonnative oysters for both aquaculture and restoration.

Maryland Natural Resources Secretary John Griffin has generally been skeptical of nonnative oyster options, while Virginia Natural Resources Secretary Preston Bryant has been more receptive. The third official involved with the decision is Col. Dionysios Anninos, who heads the Army Corps of Engineers' Norfolk District.

"There is no drop dead date by which the three jurisdictions have to come to a conclusion, though we have all said we want to do that real soon," said Jack Travelstead, fisheries director with the Virginia Marine Resources Commission. "This is a huge decision. It will be one of the most important decisions that will be made for the natural resources and health of the Chesapeake Bay, whichever way it goes. I think it's a monumental decision."

Although participants in the process have said they would prefer to agree on a common recommendation, each could make separate decisions.

During the comment period last fall, a majority supported the use of native oysters. The use of sterile oysters in aquaculture received the second most support, and an introduction of breeding nonnative oysters had the least support. East and Gulf Coast states, federal agencies and scientists strongly opposed any use of nonnative oysters. They indicated that research done during the EIS process showed that aquaculture with sterile native oysters was an economically viable alternative.

Many representatives of the seafood industry, and some lawmakers, said sterile nonnative oysters in aquaculture offered growers a greater range of options and the potential of greater profitability, with a manageable level of risk.