BANGOR — Fewer of North America’s Atlantic salmon are making it back to rivers to spawn, which bodes poorly for the future of the imperiled fish, an international conservation group says.

Atlantic salmon were once abundant in the rivers of New England and Atlantic Canada, but they are now endangered or have disappeared. The salmon are born in rivers, swim to the Atlantic and return to their natal river to spawn.

The New Brunswick, Canada-based Atlantic Salmon Federation released a report this month that says total estimated returns of the fish to North America in 2016 was a little more than a half million salmon. That is a 27 percent decrease from the previous year.

The group says young salmon that spent only one winter at sea before returning to the river, called grilse, fared especially poorly last year. They returned at a rate nearly a third lower than in 2015, the group said.

The federation warns that signs show 2017 is looking like another poor year, said spokesman Neville Crabbe.

Atlantic salmon contend with obstacles ranging from the presence of river dams to continued fishing pressure off Canada and Greenland.

Crabbe said the changing environment of the North Atlantic has also affected populations.

The report says that Greenland fishermen are catching fewer of the fish, which could be a signal of poor survival of salmon in the wild. Greenland fishermen caught less than half as many salmon last year as in 2015, the report notes.

The U.S. Fish and Wildlife Service has released a recovery plan for Gulf of Maine salmon that calls for restored habitats, removal of dams and use of hatchery programs to try to rebuild the population.

Tim Sheehan, a research fishery biologist with a National Oceanic and Atmospheric Admnisistration team, however, said it’s important to keep an eye on long-term trends in salmon population and not put too much stock in one year.