Another six months are needed to study the environmental impact of introducing Asian oysters to the Chesapeake Bay, state officials said.

Maryland and Virginia natural resource officials announced in June that a draft Environmental Impact Statement covering the risks and benefits of introducing Crassostrea ariakensis oysters into the Chesapeake will not be completed until January 2005.

It was the second time officials delayed the completion date for the full report.

But officials said chapters of the document will be made available to the public as they become final, starting with an assessment of the cultural importance of oysters to the Chesapeake, which was expected in July.

“It is important for the public to understand we are taking the time to ensure that the EIS is as comprehensive as possible, and that all available data has been considered before a decision is made on how and if to proceed,” said Mike Slattery, assistant secretary for forests, parks, fisheries and wildlife for the Maryland Department of Natural Resources.

One of the main reasons for the delay was to get more information needed for the development of models that would help predict how both the foreign and native species might be expected to fare in the Chesapeake Bay.

The delay will also allow for the inclusion of some research being funded by the National Oceanic and Atmospheric Administration’s Chesapeake Bay Office that will not be completed until fall.

The EIS is examining eight oyster management options, ranging from an outright introduction of breeding C. ariakensis oysters into the Bay to implementing a harvest moratorium on the native species.

The schedule for completing the environmental review has been contentious, though, as states have pushed for an aggressive decision-making timetable while scientists and federal agency officials have said it would take several years of research to adequately predict how the introduction of a foreign species may affect the Bay ecosystem. All of the research funded by NOAA will not be completed until the end of 2007.

The Asian oyster has stirred up huge amounts of interest because studies show that it grows fast and is resistant to diseases that have devastated populations of the native oyster. Advocates also contend that the filter-feeder would help to clean up the Chesapeake Bay.

Others say it’s not clear how the oyster would fare in the Bay, as studies suggest it is more vulnerable to predators than the native species. It’s also unknown how it would interact with the native oyster, as well as other species in the Bay.

Because of a controversy, the Maryland General Assembly this year passed legislation that would prohibit any introduction unless it is approved by a panel of scientists.