A nonnative oyster might offer some advantage over the native species for boosting oyster population levels in the Chesapeake, but restoring large populations of either would face difficulty without a long-term, and costly, commitment to restore oyster habitat.

An eagerly awaited Environmental Impact Statement that analyzed the potential for introducing a nonnative oyster in the Bay as well as other management options indicated that there's no quick fix for the Bay's longstanding oyster shortage. It indicted that building a large population will take much longer than the 10-year time frame considered in the study.

But that's not necessarily true for the commercial production of oysters. The study concluded that growing either the native or nonnative oyster in aquaculture had the potential to boost the number of market-size oysters by "several times" above the current Baywide population.

The massive document, weighing in at more than 1,000 pages when appendices are included, was prepared by the Army Corps of Engineers Norfolk District and the states of Maryland and Virginia. It is considered the most comprehensive review of oysters ever completed for the Chesapeake Bay.

Nonetheless, the report suggests that none of the eight alternatives it examined would meet both the economic and ecological goals set forth in the study. As a result, officials provided three new alternatives, each combining multiple actions.

But it offered no preferred alternative when officials released the document for 60 days of public comment on Oct. 18.

"We are not asking the public to make the decision about what our recommendation is," said Mark Mansfield, of the Corps' Norfolk District. "What we are looking for them to do is to provide input on what we've done to date. They have a voice and a say in this as well."

After reviewing public comments, a final draft including a preferred alternative will be issued early next spring. After another comment period, a final decision will be issued in late spring.

The need for the Environmental Impact Statement, or EIS, was triggered five years ago when Maryland and Virginia proposed introducing a reproducing population of the Asian oyster Crassostrea ariakensis into the Bay for the stated purpose of restoring a naturalized, self-sustaining population in the Bay.

The proposed objective was to restore the ecological role of oysters in the Bay and the economic benefits of a commercial fishery. The ultimate goal was to establish an oyster population that would reach a level of abundance in the Bay adequate to support sustainable harvests comparable to those seen from 1920-1970.

Once referred to as the "great shellfish bay" by Native Americans, the Chesapeake in colonial times was filled with oyster bars so large they posed navigational hazards. Scientists believe their ability to filter water as they feed helped to improve the Bay's water quality. Their reefs also provided habitat for many other species.

But overfishing, worsening water quality and the arrival of two diseases-MSX and Dermo-have left the oyster population devastated. Only a small fishery remains, and too few oysters are in the Bay to provide significant habitat or filtering capacity.

In recent years, interest in C. ariakensis, also known as the Suminoe oyster, has soared as laboratory and aquaculture experiments show it grows fast and survives the diseases that plague the native species, C. virginica.

The EIS concluded that a breeding population of C. ariakensis "could contribute to a substantial increase in the Baywide oyster population." But it said a host of uncertainties made it impossible to predict how rapidly the population would expand, or whether other factors might constrain population growth.

Studies cited in the EIS suggest it's thinner shell makes it more susceptible to predation, and C. ariakensis appears to suffer much greater mortality than the native species when exposed to low-oxygen conditions, a common summer occurrence for many deeper oyster habitats in the Bay. It also suffered greater mortalities when exposed to some common harmful algae species found in the Chesapeake.

The research did not reveal any "show-stopper" evidence suggesting that C. ariakensis would harm the Chesapeake. But it cautioned that any introduction of the nonnative species would likely be irreversible.

The study suggested that increased efforts to expand the C. virginica could result in a more modest increase in abundance, but that it would be restricted to low-salinity waters where there is less disease pressure and would be primarily driven by plantings of hatchery-reared larvae.

It said eliminating harvest to give larger oysters, which have survived disease, a chance to reproduce may help develop disease resistance in the native population, but it is unknown how long that would take.

Neither option is cheap. Over 10 years, nonnative scenarios could cost $500 million, while the native programs could cost $700 million, with no guaranteed outcome for either.

Those are issues that the public needs to grapple with when reviewing the options, officials said. "We are talking about a significant investment of public dollars," said Tom O'Connell, fisheries director for the Maryland Department of Natural Resources. "It is very important for the public to weigh in on whether or not they want to remain committed to a native oyster, looking at the probability of success, versus considering the irreversible risk with a nonnative oyster."

The EIS indicated that restoring the population and harvest levels to those that existed from 1920-1970 would be a daunting task. That would translate into about 12 billion market-size oysters, which could support an annual harvest of 1.4 billion oysters, or 5 million bushels, the EIS said. In contrast, only about 809 million market-size oysters existed in the Bay in 2004.

A major limitation to reaching that goal, for either oyster, is the lack of suitable habitat. Oyster larvae, or spat, need to settle on hard substrates, but sediment washing into the Bay has smothered much of their historic habitat, making it unsuitable for settlement. In addition, the Bay lacks a supply of oyster shell, which is the preferred surface for oyster settlement.

"The continuing loss of hard-bottom habitat is an overarching constraint on the likelihood of increasing the oyster population in Chesapeake Bay, whether by introducing the Suminoe oyster, or by implementing any of the other alternatives evaluated," the report stated.

A major part of the cost for both the native and nonnative options is habitat restoration.

At a news conference releasing the EIS, several officials said boosting the Baywide oyster population to the level proposed in the EIS was not feasible anytime in the foreseeable future.

"I've always felt that the Chesapeake Bay Program's objectives and goals, and this particular objective and goal, is reaching for the stars," said Col. Dionysios Anninos, the Corps' Norfolk district commander. "Whether we can achieve it or not is really questionable. And [achieving] it without a significant investment is not very realistic."

Instead of aiming for a Baywide goal, he said oyster restoration should proceed river-by-river, as some places will have a greater likelihood of success than others.

The outlook for the commercial sector is brighter, though. Aquaculture, using either the native oyster or sterile C. ariakensis oysters could eventually produce about half of the 5 million bushel harvest goal, the EIS said. It said C. ariakensis might be worth more than the native species in aquaculture because it grows faster, but said that may be offset in part because it appears less suitable for use in the lucrative half-shell market, and because it would require added biosecurity expenses to keep them from being released into the wild.

"One thing we learned through this study, in regard to the goal or revitalizing the industry, is aquaculture looks most promising, both from a native oyster perspective and from a nonnative oyster perspective," Mansfield said. Oyster aquaculture has been increasing rapidly in Virginia, and is gaining interest in Maryland.

Aquaculture, in fact, could achieve much of the commercial goal of the EIS relatively quickly, while achieving the ecological goals, which require a large wild population, could take a lot longer and cost much more.

Because of the need to build a large wild population, officials sought to separate the commercial and ecological goals.

"In reality, if you don't treat these two as two separate projects, we may not be able to achieve any of the goals," Anninos said. "There are separate sets of goals and objectives for the industry, and a separate set of goals and objectives for the ecological side."

Trying to pursue both at the same time in the past, he said, was simply "throwing resources at the problem" without making a dent in the oyster population.

As a result, the EIS proposed three new alternative options, each of which includes separate aquaculture and restoration components. All three of those alternatives also calls for a temporary moratorium on oyster harvests. In such a scenario, efforts would be made to employ watermen in restoration efforts.

Initial reaction to the EIS was mixed.

Larry Simns, president of the Maryland Watermen's Association, which has supported the introduction of a nonnative oyster, was disappointed. "It really doesn't say a whole lot. We already knew all that," he said. "As far as I'm concerned, we wasted $17 million. It's not a well-done document."

The Chesapeake Bay Foundation and The Nature Conservancy issued a joint statement supporting both aquaculture and restoration focused on the native oyster, saying it holds the best promise for citizens, the oyster industry and the Bay with the least amount of risk.

"With the right investments and management decisions by the public and private sectors, including our organizations, we can have native oyster populations that provide significant ecological and economic benefits- all without the risk of unintended consequences," added Michael Lipford, Virginia State Director of TNC.