It's been 18 years since biologists at the Northeast Fishery Center successfully spawned sturgeon at their hatchery along a Susquehanna tributary in northern Pennsylvania.

Since then, they've carefully reared the offspring from tiny "fry" to behemoths now measuring more than 5 feet in length, waiting for the day those fish would, in turn, be ready to spawn.

"I thought this might be the year," said Jerre Mohler, a biologist at the U.S. Fish and Wildlife Service research center near Lamar, PA.

But, it's not. Early indications are that none of the females, which take one to two decades to reach maturity - a process slowed by the cold streams supplying water to the hatchery - are "ripe" with eggs.

Now, Mohler worries, that long-awaited spawning may never happen.

A decision to place the Atlantic sturgeon on the federal list of endangered species has put the future of his work - and that of other sturgeon breeding programs - in doubt.

Artificial propagation for endangered species is often controversial, and scientists believe that the endangered listing will likely mean insurmountable obstacles for any sturgeon stocking program.

If so, that could abruptly end more than a decade of research that biologists once thought would eventually be used to jump-start sturgeon populations in rivers where there has been no evidence of reproduction in decades, including the Potomac and all Maryland tributaries.

"If there is not a clear path toward an introduction, I think we would have to take a hard look at terminating the program in Maryland," said Brian Richardson, a biologist who oversees the Maryland Department of Natural Resources' sturgeon efforts.

Maryland biologists conducted an experimental release into the Nanticoke River in 1996 using sturgeon reared at the Lamar hatchery. Since then, they have built up their own stock of captive sturgeon with the hope of breeding them and producing young for potential release.

But the endangered listing means that any such stocking program must first be approved by the National Marine Fisheries Service, which is now responsible for sturgeon recovery. That could be a tall order because, technically, most of the fish Maryland is rearing are not native to the Bay.

The NMFS, in its listing decision, considers the entire Chesapeake to be a "distinct population segment," or DPS.

"If you are going to put stock into a particular area, you should be stocking fish from that DPS into that particular area," said Kimberly Damon-Randall, the biologist overseeing protected species in the NMFS' Northeast Regional Fisheries Office in Massachusetts.

Anadromous fish such as sturgeon return to their native rivers to spawn, and the populations vary genetically from river to river. Biologists believe that variation makes each stock uniquely adapted for conditions it encounters within its native river. Generally, the farther rivers are apart, the greater the genetic variation.

Maryland has been collecting fish from its portion of the Bay for more than a decade to build a brood stock to eventually produce young for a potential reintroduction. While genetic analysis shows many of those are from the James River, most were just passing through from other river systems, such as the Hudson, which are not part of the Chesapeake DPS.

"We would have to review that very carefully," Damon-Randall said. "There is a unique Chesapeake Bay DPS, and so to then introduce fish from someplace else could be problematic."

But a reintroduction program relying on Chesapeake fish has its own problem. There is only one source - the James River, and its population is thought to number only a few hundred.

Protocols drafted for sturgeon more than a decade ago by the Atlantic States Marine Fisheries Commission called for stocking programs to use eggs and sperm from at least 100 individuals to ensure adequate genetic diversity and prevent inbreeding. It seems unlikely, if not impossible, that that many fish could be secured from the James without threatening that population.

Stocking proponents worry that without a reintroduction program, it could take many, many years for sturgeon populations to increase enough to recolonize river systems on their own, especially because it takes one to two decades for them to even reach maturity.

"It could take centuries to happen," said Steve Minkkinen, a former DNR biologist who oversaw the 1996 Nanticoke stocking and now heads the USF&WS Maryland Fisheries Resource Office.

On the flip side is the potential to do unintended harm. If, for instance, fish from the Hudson were stocked in the Potomac, and they eventually bred with the remnant population in the James River, it might result in offspring more poorly adapted to survive in the James, potentially harming efforts to recover that population.

Damon-Randall said any stocking proposals would have to be decided on a case-by-case basis, but said it might be less risky to better protect the James population and allow it to grow and expand over time. "If we can get their numbers back up in areas in Virginia where they already still are, they might on their own recolonize Maryland without any need for a conservation hatchery program," she said. "But those are all things that we would have to look into."

Without assurance that a reintroduction would be permitted, Richardson said it would be difficult for Maryland to spend increasingly limited funds to maintain its captive sturgeon population.

"It comes down to risk/reward," Richardson said. "How much of our constantly shrinking resources can we dedicate to something if we don't know the potential outcome?"

Maryland's situation is not unique. The USF&WS' Bears Bluff National Fish Hatchery in South Carolina had been considering using hatchery-reared fish to reintroduce sturgeon into the St. Mary's River, on the Georgia-Florida border, to help build public interest in a river that was once heavily polluted but has recovered in recent years. Now, they may stock striped bass instead.

Likewise, Mohler said Lamar biologists are uncertain whether hatchery-reared sturgeon will be part of any recovery program, either to jump-start populations in rivers where sturgeon are gone, or to bolster numbers of fish in places with only remnant populations.

"If they are, then it would behoove us to try to keep the fish we have," he said. If not, he said, new restrictions that come with any endangered species listing would likely make sturgeon - already difficult to work with because of their size - more cumbersome to maintain.

If hatchery programs come to an end, it could ironically mean a death sentence for some sturgeon once eyed as the building blocks for restored populations.

Maryland has 44 captive brood stock fish, ranging from a foot-and-a-half to 5 feet in length, which had mostly come from the Bay. Most of those fish can probably be released back into the Chesapeake, Richardson said. But it also has a number of hatchery-reared fish from the Lamar facility that came from Hudson River fish, and their fate is uncertain.

The state has 400 to 500 Canadian fish that range from 1 to 6 years old that were being used to help understand and improve hatchery techniques, and another 1,000 were hatched from the Canadian stock last year.

Some of those might be lent to researchers, Richardson said, but others would likely be euthanized if the hatchery program is discontinued; everyone agrees the Canadian fish cannot be released into the Bay.

The Lamar hatchery has about 60 hatchery-reared sturgeon, from 4 feet to more than 6 feet in size. All were bred from Hudson River fish, but all have spent their lives in water from the Susquehanna watershed, which might be problematic.

Mohler thinks he might be able to return the fish to the Hudson River - if New York officials decide they want them. "I think everyone that is holding fish right now is in a holding pattern," he said.