American eel numbers are low, but stable, along the East Coast and do not warrant protection under the Endangered Species Act, a multiyear federal review has concluded.

Eels — once one of the most abundant fish in many freshwater streams — have suffered large population declines over the last century, but the U.S. Fish and Wildlife Service, which had rejected a petition to list eels as threatened or endangered in 2007, said little had changed since that decision, and Wednesday rejected another request to list the species.

“Despite historical habitat losses and a population reduction over the past century, American eels remain widely distributed throughout a large part of their historical range,” the USFWS said in its decision.

If eels had been listed as a threatened or endangered species, it could have had a significant impact on the region, as about two-thirds of the eel harvest in the United States takes place in the Chesapeake Bay.

American eels may live in more distinct aquatic habitats than any other species. They spawn in the mid-Atlantic's Sargasso Sea, but spend much of their lives in estuaries and freshwater rivers, lakes, streams — even ponds. They can live in those areas for one to two decades, before returning to the Sargasso to spawn.

They were once hugely abundant — often accounting for a quarter of the fish biomass in many freshwater streams. But like many other long-distance migratory species, their populations have declined dramatically in recent decades. Construction of dams blocked access to habitats and overfishing, pollution, the introduction of exotic parasites and climate change have all been blamed for playing a role in the decline of eels.

Because of such concerns, the International Union for Conservation of Nature last year updated its Red List, and included the American eel as endangered, although that listing does not have regulatory authority.

A recent stock assessment by the Atlantic States Marine Fisheries Commission, which regulates the eel harvest along the East Coast, reported the species to be “stable but depleted.”

An environmental group, The Center for Environmental Science, Accuracy and Reliability in 2010 petitioned the USFWS to reconsider protecting eels under the Endangered Species Act.

The service in 2011 agreed to re-examine the issue, but after four years reached the same conclusion — although eel numbers are at historically low levels, none of the threats facing the population, either individually or cumulatively, were likely to cause the species to become endangered or extinct in the foreseeable future.

It also noted some positive actions had been taken since its 2007 decision. The ASMFC has further restricted harvests and  the Federal Energy Regulatory Commission increasingly requires eel passages at hydroelectric dams when they come up for relicensing.

The service did acknowledge some concerns, such as the growing demand for very young “glass” eels for use in Asian aquaculture operations. That demand is the result of a ban on the export of European eels, which are also at low levels, to Asia.

The price for glass eels has grown sharply in recent years, and although their harvest is regulated by the ASMFC, many officials are concerned that potentially large numbers are caught illegally. The service said it did not presently consider international trade or illegal harvests a threat to the overall eel population, but it noted that international trade in eels could be regulated in the future.

The American eel is being considered for inclusion under the Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES). If that happens, any export of eels would be regulated under the convention. “Given the international demand for American eels that drives some domestic harvest, regulation under CITES could complement ASMFC’s domestic regulation of the species,” the service said.

The ASMFC issued a statement saying it was “encouraged” by the decision not to list the eels as threatened or endangered, saying its management programs were already working to reduce mortality and improve the conservation of eels.

“However, given the current depleted status of the resource, there is still considerable work to be done to rebuild the American eel,” Commission Chair Louis Daniel, III, said. “The Commission will continue to closely monitor American eel fisheries and the status of the resource, and make adjustments to the management program as necessary, to ensure stock rebuilding.”

American eels have been a key species targeted by the state-federal Chesapeake Bay Program for restoration in the region; dam removal and fish passage projects are being designed to help eels.

An ongoing effort in recent years has trucked almost a million eels past dams on the lower Susquehanna River to reintroduce them to the Bay’s largest tributary, from which they have been absent for nearly a century. Eel passage at the Conowingo Dam on the Susquehanna is expected to be a condition of a new operating license for the dam.