SALMON, Idaho (Reuters - A small group of killer whales in the Pacific Northwest faces extinction unless U.S. government fisheries managers reverse a decline in their main food source, Chinook salmon, scientists said on Monday.

The orcas there made headlines this year when one of the group’s last remaining reproductive females towed her dead calf for 17 days in a show of mourning.

Their population might rebound if Chinooks are restored in the Columbia River Basin, the scientists said in a letter on Monday to a panel tasked with saving the so-called southern resident killer whales.

Dams and habitat destruction have severely cut their numbers in the area, orca advocates and researchers wrote to the Southern Resident Killer Whale Task Force and to Washington state Governor Jay Inslee.

The task force that Inslee created in March is finishing a report spelling out measures needed to recover the famed whale population, which spends the greater part of each year pursuing salmon along the Pacific Coast off Washington state. The orcas there now number just 74, a 35-year low.

In his executive order establishing the task force, Inslee said threats to these orcas include a lack of prey – orcas feed mainly on Chinook – waters polluted by toxins, and disturbance and noise tied to ship and boat traffic.

In their letter, University of Washington scientist and orca activist Dr. Deborah Giles and five co-authors urged the task force to advise Inslee to take immediate action to replenish Chinook salmon runs in the Columbia Basin, particularly the Snake River spring run that mostly spawns in Idaho streams.

They called for dismantling four hydropower dams in the lower Snake River, which they say hamper Chinooks’ seasonal migrations to and from the Pacific Ocean.

The scientists said salmon restoration is crucial to save the three pods that make up the southern resident killer whale population.

“Indeed, we believe that survival and recovery may be impossible to achieve without it,” they wrote.

A spokeswoman for Inslee said he appreciated the input, adding: “We will weigh in on the aspects of the recommendations once we receive them from the task force.”

The panel’s final report is expected next month.