Last year’s images of the orca Tahlequah carrying her dead calf for more than two weeks sparked a discussion about how humans have reshaped the natural world and how to intervene on behalf of the endangered southern resident killer whales before it’s too late.

For Tahlequah’s mother, J-17, that time has come. She and two other orcas are now presumed dead, according to the Center for Whale Research. The population of Washington’s endangered southern residents is now 73, a 40-year low.

As advocates and researchers count the latest casualties, many have renewed calls for enacting measures that would increase the orcas’ food supply and ultimately ward off their extinction. At the bedrock of one debate over what to do next are the four Lower Snake River hydroelectric dams, managed by the U.S. Army Corps of Engineers and the Bonneville Power Administration, which markets the power they produce. Critics believe they have propelled the orca’s gradual starvation over the last 40 years by interrupting crucial salmon runs.

While many experts agree with restoring lost habitat, they say the obstacles facing the whales are vast and will likely only expand with time unless comprehensive change is initiated quickly.

“There is broad recognition that the major and most urgent drivers for orca decline in that population facing extinction today are lack of food and lack of Chinook salmon, which [orca] need in far greater abundance than exists now,” said islander Joseph Bogaard, executive director of Save Our Wild Salmon.

According to Bogaard, the Columbia and Snake rivers are key pieces of the puzzle in the orcas’ decline. While many believe that the dams in the region have upended the existence of spawning salmon for a generation — and in turn, the orcas — Save Our Wild Salmon is measuring their impact in another way, by taking weekly, up-to-date temperature readings of the reservoirs behind each. They are watching for the water to exceed 68 degrees Fahrenheit, or the threshold when salmon and steelhead begin to suffer harmful effects, from reproductive issues to exhaustion and death.

The water in the reservoirs behind the dams in the Columbia and Snake rivers doesn’t move far, and as the summer months roll on, it absorbs solar radiation from the sun and heats up. Save Our Wild Salmon predicts that a warming climate will fundamentally alter the ecosystem in ways that could weaken and kill migrating juveniles and returning adult salmon.

“In the Pacific Northwest, we have not properly stewarded the ecosystem upon which the salmon and orca, and we, depend. And the problems are multiplying,” said Bogaard. “These rivers are getting warmer, and especially dangerous in the summer months, to the point that it is one more pressure point on already endangered salmon populations.”

The federal government has a response for some instances of warming in dammed reservoirs. The Dworshak Dam, on the North Fork Clearwater River in Idaho, benefits from a much deeper, cooler reservoir of water relative to other federal dams, particularly on the lower Snake. Hot weather conditions prompt the release of colder water held at Dworshak, which takes about three days to reach the downstream side of the Lower Granite Dam on the Snake River, according to the Army Corps of Engineers. But Bogaard said it isn’t enough to make a difference across the lower Snake.

“These fish are highly adaptable, highly resistant, but they have their limits. Our inaction … is pushing them past their limits,” he said.

Locally, King County is targeting the well-being of migrating salmon with the recent acquisition of nearly 4 acres in the Maury Island Aquatic Reserve, including tidelands and waterfront, after $45 million in funding was awarded to projects to improve salmon habitat and shoreline health across the state last month.

The county Water and Land Resources Division will lead the removal of 50 feet of shoreline armoring at the site, one part of a larger investment to restore a number of parcels on Vashon while facilitating the activity of chinook and coho, cutthroat trout, and forage fish such as sand lance, surf smelt and Pacific herring.

Janne Kaje, a supervisor at the Department of Natural Resources and Parks, said the county is interested in finding property owners who are willing to sell. The goal is to one day reverse the damage wrought on habitat by bulkheads armoring the shorelines of acquired parcels. Those barriers obstruct the natural movement of sediment that erodes from neighboring bluffs, ordinarily creating vital tidelands essential to forage fish. Juvenile salmon, he said, frequent nearshore areas such as the aquatic reserve during their migration, often eating forage fish and their eggs.

“We want those beaches to be in good condition for that,” said Kaje.

The acquisitions are targeted, he added, and the county pays market value.

“Any of this type of restoration and acquisition work is dependent on us obtaining many different sources of funding, both local and state,” he said.

Amy Carey, a member of the orca task force’s prey availability working group convened by Gov. Jay Inslee last year, said that the Legislature needs to support more habitat improvement work across the state that cannot be neglected any longer or held up in the next session.

“There are so many shovel-ready restoration projects, and the state and fed, they continue to not fully fund them, and those things really need to happen,” she said, cautioning against “feel-good exercises” that don’t advance protections in a meaningful way. “It is a very, very high price tag to fund all of the thoroughly vetted restoration projects that all of the salmon experts have had for years. We have [still] got to fund that.”

Carey said last week’s news about the three orcas was a gut punch that she expects will be a catalyst in the work group’s meeting this week.

“We’ve made some progress, but it’s that reminder [to go] boots on the ground and full steam ahead right now, and try to do everything we can,” she said.

Ann Stateler and Odin Lonning of the Vashon Hydrophone Project were on San Juan Island standing in friend and researcher Bob Otis’s whale lab in Lime Kiln Lighthouse last week when they heard about the orcas. Otis’s long summer study of whales between the months of May and August — nearly 30 years in the making — has reached a turning point recently, said Stateler, because there have been no orcas to observe.

“This is the first year ever that we did not see southern residents anytime during the summer when we went up. That’s unprecedented,” she said.

On a calendar inside the lab, Otis marked two days of whale sightings for the entire season, on July 5 and 6.

The news about the vanished orcas did not come entirely as a shock to Stateler. Tahlequah’s mother, J17, and K25, a 28-year-old male, were not in good body condition when they were last seen.

“It’s just been really heartbreaking and soul-crushing to watch what’s happening,” said Stateler, noting her distress over reports that the orcas are seeming to avoid what was once their primary habitat in the summer, between the Strait of Juan de Fuca and Haro Strait.

Last year, NOAA Fisheries analyzed chinook salmon stocks and found that the southern resident orcas depend in large part on salmon leaving the Fraser River in British Columbia, Canada. It is now the focus of an intense cleanup effort after a major rockslide made the channel impassable to the fish last month. Stateler said with that blocked, and little to sustain them as it is, the orcas headed elsewhere — farther north, spotted off the wild west coast of Vancouver Island as recently as this week.

Stateler said the whales may have found a larger cache of salmon to eat, free of acoustic disturbances from vessel interference, which impedes their ability to use echolocation to find their food.

Malnourishment and starvation, Stateler said, are real dangers for the orcas, but she noted they may also trigger a worse problem — starving whales begin to metabolize their blubber, which may unleash toxins that have accumulated in their fat, compromising their immune systems and leaving them susceptible to disease.

“There’s this interaction of all these threats to whales,” said Stateler, wondering if the orcas may one day leave the Salish Sea for good because it is no longer hospitable for them.

“Native people recognize that this is a spiritual crisis. We feel that this is a spiritual crisis, that the southern residents don’t feel welcome inside the Salish Sea right now,” she said, calling for a genuine redress of the situation instead of empty promises, and more than the “tepid incrementalism” she accused the task force of trading in.

“The whales are dying in droves. We need to pull them out of this death spiral,” she said.