Populations of river herring may be at low levels along the East Coast, but the small fish are not likely to disappear and do not warrant protection under the Endangered Species Act, a federal review has concluded.

In 2011, the Natural Resources Defense Council had petitioned for the fish to receive protection as a threatened species under the act, saying overall numbers of alewife and blueback herring — collectively known as river herring — were a “tiny fraction” of their historic abundance.

But in August, the National Marine Fisheries Service concluded that available information indicated that alewife stocks along the East Coast were generally either stable or increasing. The situation for blueback herring was slightly worse: Some stocks were stable, but those in the mid-Atlantic were decreasing.

Overall, the review said the risk of alewife extinction was small, while the risk of blueback herring extinction was moderate-low. While not threatened or endangered, the review did agree that both stocks were low compared with historic levels, and that available data for both species is often poor.

“Given the uncertainties and data deficiencies for both species, we commit to revisiting both species in three to five years,” the service, a part of the National Oceanic and Atmospheric Administration, said in its findings.

River herring are anadromous species that spend most of their lives off the Atlantic Coast but return to their native rivers to spawn. They historically returned to coastal rivers in phenomenal numbers each spring, vastly outnumbering their larger cousin, the American shad, and typically swimming farther upstream to spawn. But the construction of dams, pollution, loss of habitat and overfishing — especially in the late 1960s and early 1970s when foreign fishing fleets off the East Coast took a heavy toll — left the species at a fraction of their historic level.

Because of their low levels, the Atlantic States Marine Fisheries Commission, which regulates fisheries in state waters, closed almost all river herring fisheries, including those that remained in the Chesapeake, last year.

In July, the Mid-Atlantic Fisheries Management Council, which regulates catches in federal waters — those more than three miles offshore — took action to limit the amount of river herring and shad caught as accidental bycatch in the mackerel fishery. Anecdotal evidence suggested that large numbers of river herring were being caught in the fishery.

In releasing its findings, the service said it would work with the ASMFC and others to improve river herring data and to develop and implement a long-term plan to protect river herring and their habitats from Canada to Florida.

“We plan work with our partners to identify and implement effective conservation efforts for river herring populations throughout their range while also supporting further research to fill in important data gaps for these two species,” said John Bullard, administrator of the service’s Northeast region, which conducted the review.

The Herring Alliance, a group of conservation groups which includes the Natural Resources Defense Council that is working to protect the fish, called the service’s decision “disappointing” and expressed doubt about its willingness to fully address issues affecting river herring.

It noted that the service recently rejected a plan approved last year by the New England Fisheries Management Council to sharply increase the use of observers on fishing vessels to monitor bycatch because of its cost.

“With [Endangered Species Act] protections off the table for now, regional fisheries managers must take strong action to reduce the at-sea catch of river herring and protect the ocean habitat of these imperiled fish,” the group said on its website.

River herring, along with other species of forage fish, have increasingly been targeted by conservation groups for greater protection in recent years because of their important role as food for other species.