Atlantic sturgeon, an ancient species that co-existed with dinosaurs, has fared less well sharing coastal and river habitats with humans. As a result, they will be officially protected as an endangered species beginning April 6.

The decision by the National Marine Fisheries Service means it believes the sturgeon, the largest fish native to the Chesapeake - historically they reached lengths of 14 feet - is likely to become extinct in the foreseeable future without additional protection.

The NMFS, an arm of the National Oceanic and Atmospheric Administration, has not yet stated what new actions it will take to protect sturgeon, which are already subject to a coastwide fishing moratorium.

But its decision issued Feb. 6 said that sturgeon are taken as bycatch in other fisheries, killed by ship strikes, squeezed out of historic habitat by poor water quality and face other problems - all of which may be targeted for future protection efforts or regulations.

The decision by the NMFS came after a review sparked by a 2009 petition from the Natural Resources Defense Council that argued existing measures were not protecting the giant fish.

"Despite a more than decade-old ban on fishing for the sturgeon, a host of other threats - including ongoing catch in other fisheries, habitat damage, pollution and the growing effects of climate change - have proved too challenging for the species to recover," said Brad Sewell, a senior attorney with the environmental group.

"By recognizing the fish's endangered status, the federal government is giving this remarkable fish a fighting chance to live on into the 21st century."

But the endangered listing will set back some sturgeon work in the Chesapeake. Programs in both Maryland and Virginia that work to tag and release sturgeon that get caught in fishing gear are coming to an end. And the future of a captive breeding program aimed at returning sturgeon to Maryland tributaries where they've been gone for decades is in doubt.

Sturgeon are an anadromous species, meaning they spawn in freshwater portions of rivers but spend most of their lives migrating along the coast before returning to spawn in their river of origin.

Once abundant, sturgeon were heavily fished for both their meat and eggs in the mid to late 1800s, decimating the population. Because females do not reach sexual maturity until they are 15 or more years old, it was difficult for the population to rebound, especially as pollution, dredging and other activities degraded habitats.

Sturgeon have vanished from many of their historic breeding grounds, including all of those in Maryland. In places where they remain, such as the James River, their numbers are a fraction of historic levels. Capt. John Smith once described the river as having more sturgeon "than could be devoured by dog and man."

The NMFS's decision, which was finalized Feb. 6, listed all populations along the East Coast as endangered except for those in the Gulf of Maine, which it listed as threatened.

But the decision - at least as it relates to the Chesapeake - was criticized by some, who say the James River breeding population appears to be rebounding on its own.

"We feel the decision is not a responsible use of the ESA, is not based on the best available science and poses an unnecessary existential threat to a broad range of economic and recreational activities on the entire Atlantic Seaboard," said Kelly Place, director of research and policy with the Virginia State Waterman's Association.

Place, who has worked with scientists on sturgeon studies in the James, said the fish seem more plentiful today than they did in 1998, when an earlier federal review determined that protection under the Endangered Species Act was not warranted.

The NFMS said in its decision that it was unclear whether the numbers of sturgeon in the James had in fact grown, or whether increased observations were the result of recent efforts to study sturgeon in the river. It also said it was unclear whether all of the fish observed were native to the James, or were fish from other systems that had ventured up the river.

Others are worried that the listing could hamper work on the fish. The NMFS is working to accelerate the issuance of research permits needed by scientists who work on sturgeon around the Bay. But those permits will not cover programs in Maryland and Virginia in which fisherman hold sturgeon caught in their gear until biologists tag and release the fish. "The kicker there is, probably most of our data on sturgeon have come in work with commercial fishermen," said Albert Spells, who heads the U.S. Fish and Wildlife Service Virginia Fisheries Resource Office.

The holding of sturgeon by fishermen would be considered a "take" which is prohibited under the Endangered Species Act. That includes any activity that kills, harasses, captures, collects or otherwise harms a protected species. While special permits can allow those activities, they can be time-consuming to obtain. Consequently, the Maryland tagging program ended Feb. 16, and the Virginia program will end April 5 - the day before the fish officially become endangered.

"The thing I've been afraid of all along is that if you go the endangered species route, you can really know a whole lot less about what is going on," said Steve Minkkinen, who heads the U.S. Fish and Wildlife Service Fisheries Resource Office.

Until sturgeon monitoring programs were launched in Maryland and Virginia, many biologists thought sturgeon were extinct throughout the Bay. But the programs helped provide evidence that a small breeding population persists in the James River. There have also been hints of breeding in the York.

There has been no evidence of any breeding in Maryland tributaries, but the 2,300 fish caught in the state's tagging program since 1996 showed that large numbers of sturgeon from other rivers, such as the Hudson, periodically swim through the Bay, possibly in search of food. The program allowed biologists to track the tagged fish and learn what habitats they were using.

Dave Secor, a fisheries biologist with the University of Maryland Center for Environmental Science who has studied sturgeon, said there were signs that sturgeon populations in many areas along the East Coast were recovering.

On the other hand, he said recent studies showed the threat to sturgeon from bycatch in other fisheries was growing, yet management agencies had not responded to those concerns.

"I think some of these important issues will get traction with the new [endangered species] management regime," Secor said. "But the new management regime tends to be a little bit more rigid than the old ones."

Kimberly Damon-Randall, the biologist overseeing protected species in the NMFS' Northeast Regional Fisheries Office in Massachusetts, said evidence that sturgeon bycatch was "much more significant than previously thought" was an important factor in the endangered species listing.

She said the NMFS would be working with the Atlantic States Marine Fisheries Commission, which manages fisheries within 3 miles of the coast, and regional fishery management councils that regulate catches in federal waters more than 3 miles offshore to enact measures that protect sturgeon.

State fishery officials are waiting for word about what changes might be needed in some commercial fisheries, including those for striped bass.

"We honestly don't know where this goes from here," said John Bull, a spokesman for the Virginia Marine Resources Commission. "But we are quite concerned because we have a very large gill net industry and a commercial fishing industry that could potentially be seriously impacted by this listing."

Research shows that anchored gill nets can greatly reduce sturgeon catches if openings are left at the bottom of the nets, and sturgeon mortality is reduced if the nets are checked at least once a day.

It's also possible the listing will result in new efforts to protect sturgeon from ship strikes. Biologists working on the James say a number of large sturgeon appear to have been killed by big ships in recent years.

Damon-Randall said the NMFS would meet with port authorities and others along the coast to identify measures that might help protect sturgeon, such as potentially reducing speeds in some areas.

Some protections would likely have little impact on the Bay. The Chesapeake Bay water quality standards, which drive cleanup efforts throughout the watershed, would not be affected because they were written to protect sturgeon, which are one of the fish most sensitive to low-oxygen conditions.

Also, the presence of shortnose sturgeon, a smaller cousin of the Atlantics that have been listed as endangered for more than four decades, means that many construction and navigation projects around the Bay already take sturgeon into consideration.

The listing may be a sign of things to come in the Bay. The U.S. Fish and Wildlife Service is exploring whether American eels should be listed as a threatened species under the Endangered Species Act, and the NMFS is considering whether river herring - alewife and blueback herring - should be listed. Populations of all those species are thought to be at, or near, historic lows in the Bay and along the East Coast.