Three years after Virginia imposed heavy restrictions on crabbing, the iconic blue crab is making a comeback in the Chesapeake Bay. There are more than 460 million, almost double the population four years ago.

But a groundbreaking federal assessment of the crab population released Tuesday says that trend could be reversed if Virginia bows to pressure from state watermen and other groups to loosen the restrictions. Virginia crabbers are calling on the state to open the lucrative winter dredgery near Hampton Roads, where females skitter to hibernate during pregnancy and lay eggs.

The assessment by the National Oceanic and Atmospheric Administration said that raising the number of female crabs, from about 160 million to 215 million, is key to sustaining the population and perhaps bringing it back to its previous strength of 828 million. The assessment is the first to estimate the population of adult crabs by gender and to study their biology to determine how many offspring they can reasonably produce based on their life cycle.

The Virginia Marine Resources Commission is scheduled to meet Aug. 23 to discuss proposals to open the dredgery and allow watermen to use more than the current allotment of about 350 crab pots.

In a statement about the federal assessment, Virginia’s fisheries chief, Jack Travelstead, indicated that the dredgery near the mouth of the bay could remain closed. “This new science indicates we have a way to go to achieve our goal of having a biologically stable stock with a robust harvest,” he said. “This is a sea change in how we will manage the fishery.”

Ken Smith, president of the Virginia Waterman’s Association, was livid. “I think it’s nothing more than politically based science,” Smith said. “I’m tired of watermen getting the short end of the stick.

“Constantly the Virginia watermen have done nothing but obey the laws and regulations put on them, and then it changes,” Smith said. “We’ve done this thing for three years like we were told to do it, and we were told they would come back and relax the regulations. They have plenty of crabs on the bay.”

Thomas Miller, director of the University of Maryland Center for Environmental Science’s Chesapeake Biological Lab, said past assessments couldn’t provide the same level of data as the latest study.

“We weren’t able to do that in the past for a couple of reasons: We didn’t have sex-specific data because there wasn’t enough collected, and the field of assessment science hadn’t improved,” he said. “Now there is software that helps us understand the crab’s biology.”

The marine resources commission said there is a clear relationship between harvests by the watermen and steep declines in crab populations, according to the Bay-Wide Winter Dredge Survey.

In 1991, when there were 828 million crabs, watermen harvested 90 million pounds of the crustacean. The next year, there were 367 million crabs. In 1997, when there were 678 million crabs, watermen fished out 77 million pounds. The next year, there were 353 million crabs.

Miller said that allowing watermen to capture female crabs soon after mating “wouldn’t be a good idea” because those crabs mate twice more. Harvesting them would eliminate three broods of crabs.

Carl Tobias, a professor of law at the University of Richmond who focuses on legal questions about the blue crab fishery and the bay, said the watermen have a right to question the fairness of limiting the harvest.

“I think it’s going to be difficult to figure out how to regulate in a way that doesn’t continue to be harmful to the watermen,” Tobias said. “I think that meeting will be a difficult one, and the watermen will show up in force.”