East Coast fishery managers are calling for emergency action from the federal government to control the bycatch of river herring in ocean fisheries in an attempt to reverse the sharp decline of blueback herring and alewife.

Millions of the small fish once flooded Chesapeake Bay tributaries during their spring spawning runs, but those migrations have dwindled to a trickle in recent decades as populations hit historic lows around the Bay and in most other East Coast rivers.

While a number of factors may contribute to the decline, fishery managers suspect that large numbers are caught by fishermen targeting other species in federal waters-those more than three miles off the coast, where river herring spend most of their lives.

The Atlantic States Marine Fisheries Commission, a panel of state fishery managers that regulates migratory fisheries in state waters, agreed in May to ask Commerce Secretary Gary Locke to take emergency action to control bycatch in federal waters.

The National Oceanic and Atmospheric Administration Fisheries Service, which manages fisheries in federal waters, is part of the Commerce Department.

"Calling on the secretary for emergency action was a bold statement," said Pam Gromen, executive director of the National Coalition for Marine Conservation, one of many conservation groups that had pushed for action to control bycatch.

Coastwide, river herring landings have dropped more than 90 percent over the last two decades, a decline that is reflected in the Bay as well.

River herring are often overshadowed by their cousin, the American shad, which is the target of multimillion dollar restoration efforts, and whose return each spring is eagerly awaited by recreational fishers.

But historically, river herring greatly outnumbered shad. In the 1830s, as many as 750 million herring were taken during an eight-week spawning season on the Potomac River compared with 22.5 million shad. River herring swam into smaller creeks than shad, providing a marine food source for predatory fish, which is important to fuel freshwater ecosystems. One early Chesapeake historian wrote that spring herring runs were so great that "even the freshest of rivers...stink of fish."

Those days are in the distant past. The coastwide catch of blueback herring and alewife has declined from 13.7 million pounds in 1985 to about 1 million pounds. Four states have closed their waters to river herring catches.

Alewife and blueback herring are anadromous fish species, spending most of their lives in coastal waters but returning to their natal rivers to spawn. Historically, state commercial fisheries took place in individual rivers, where harvests could be managed based on the status of the spawning population using that waterway.

But when the fish swim into the Atlantic, populations from different rivers mix, so any catches have the potential to affect populations from all river systems. Some areas where blueback herring and alewife spend the winter overlap with those targeted by small-mesh trawl fisheries, which catch such species as Atlantic herring and mackerel in federal waters.

Bycatch in those fisheries is poorly monitored, as few observers are on the fishing boats. Also, various species of shad and herring are difficult to tell apart.

Limited studies suggest that the amount of alewives and bluebacks taken in the small-mesh fisheries could be twice the annual harvest from state waters.

Further, those studies hint that large numbers of shad-whose population has also plummeted in recent years-are also being caught. In 2007 and 2008, "unidentified herring and shad" in the bycatch outnumbered confirmed American shad, hickory shad, alewife and blueback herring combined by a 7-to-1 ratio.

"I definitely would like to include some monitoring criteria that would help solve the mystery of what is happening with shad," Gromen said.

The ASMFC urged Locke to take emergency action to step up bycatch monitoring in federal waters, a move that could result in new restrictions.

"Hopefully they are going to put more observers on these boats so we have a better sense of what the bycatch looks like, and from there we can look at what management measures we need," said Brooks Mountcastle, mid-Atlantic representative for the Marine Fish Conservation Network. "If there is a bycatch occurring within federal waters, they have a responsibility and obligation to address it."

Under the ASMFC's action, states also must monitor river herring bycatch in state waters. And they must close any commercial or recreational fishery that targets river herring unless they can show by 2012 that those fisheries are sustainably managed.

River herring fisheries used to be important in the Chesapeake and its tributaries, but catches have diminished sharply. Only a handful of watermen target the species; most river herring caught in Maryland and Virginia are caught as bycatch in pound nets or fyke nets.

"There will be less of an impact than if it was 10 or 15 years ago," said Rob O'Reilly, a fisheries scientist with the Virginia Marine Resources Commission. "Certainly, there is not a lot of directed fishing mortality."

The most difficult task, O'Reilly said, will be trying to assess the amount of fish caught by recreational fishermen, as the state has no mechanism to monitor that catch.

While bycatch is thought to be a major source of river herring mortality, other factors may contribute, including a growing number of predators.

"We see occasional strong year classes with lots of juveniles produced," said Robert Sadzinski, a Maryland Department of Natural Resources fisheries biologist who chairs the ASMFC technical committee responsible for river herring. "But then they have to run the gauntlet of striped bass in the Bay, and we don't see those strong year classes coming back three, four, five years later. So there is something happening between the juvenile stage, and when they return as adults."

The decline of river herring spurred the NOAA Fisheries Service to designate them as a "species of concern" in 2006.

Mountcastle held out the possibility that conservation groups could pursue stronger actions if the river herring decline is not reversed.

"There is a chance that they could be petitioned for listing under the Endangered Species Act if the numbers continue to decline," he said. "The economic impact will be far greater if we go that route, and clearly we don't want to. But if the numbers are such, the conservation community may have to do that."