The reported deaths this week of three more southern resident orcas have brought renewed urgency to efforts to save the critically endangered population of whales. Many scientists and policymakers are focusing on the orcas’ access to their main source of food, the Chinook salmon. Members of the orca population are appearing dangerously thin and malnourished. But is the drop in their numbers the result of a lack of Chinook? It is an increasing matter of debate among scientists.
By Jeff Rice, Puget Sound Institute
As the population of southern resident killer whales continues to decline, media outlets around the world have reported that Puget Sound’s orcas are dying of starvation.
“A pod of orcas is starving to death,” read The Guardian newspaper in London, as word went out last summer that a mother orca had carried her dead calf for a thousand miles. A headline in The New York Times reported, “Orcas of the Pacific Northwest Are Starving and Disappearing.”
These headlines echo a commonly held belief about orcas and their food supply, but are they accurate?
Studies have shown that the fish-eating southern residents prefer Chinook salmon over any other type of fish, and Chinook numbers have fallen far below historical levels. In Puget Sound, Chinook salmon are so depleted that they are listed under the federal Endangered Species Act. Food is critical to any population, so it’s not a huge leap to tie the Chinook decline to the decline of the southern residents.
In Washington state, the governor’s Orca Recovery Task Force established a primary goal of increasing the number of Chinook available to the orcas by boosting hatchery releases, improving habitat for wild salmon and considering ways to reduce the number of harbor seals — another species known to eat Chinook.
While many scientists agree that improving prey availability is important to southern resident orca recovery, some argue that there is no clear evidence that the whales are starving to death. They point to other possible factors, such as disease and genetic conditions related to inbreeding within the small population. Others would go even further, saying that there is little to no evidence that a current lack of salmon is affecting orca populations at all.
If this is news to many in the public, it’s been a hot topic of discussion happening outside the glare of the headlines, at symposiums, in scientific papers and in government hallways. We asked several prominent orca and fisheries scientists the same question: “Are Puget Sound’s southern resident orcas dying because of a lack of Chinook?” Their answers might surprise you.
Are the orcas starving?
“It is not a settled question,” says NOAA wildlife biologist Brad Hanson of the Northwest Fisheries Science Center.
Hanson, for his part, cautions against the use of the word starvation. He is audibly frustrated when he hears the word used in connection to orca declines.
“That’s part of the problem,” he says. “I think there has been an effort to simplify the problem and so the default answer is the animals are starving. That’s something that in general people can easily wrap their heads around. But in reality, that’s not quite accurate.”
Hanson made this point in a podcast earlier this year that outlined the many problems facing southern resident orcas, from low salmon runs to noise and pollution issues.
When Hanson began studying orca declines 15 years ago, he hoped the causes would be simple to identify, “but what we’re finding is that is not the case.”
Here’s what Hanson wants you to know:
Like all animals, orcas need food to survive. And yes, Chinook populations throughout the southern residents’ range have declined from historic numbers, so overall availability is not what it was historically. But Hanson is inclined to see the lack of food as a stress on the population, not necessarily the direct cause of the highly-publicized orca deaths.
“If lack of food, or access to it, was causing starvation we would expect to see it across families, pods, or the entire population but we don’t see that,” he says.
The question of starvation is more than an issue of semantics, he argues. It goes to the core of understanding orca declines and finding the most effective path to recovery.
If an animal is losing weight, Hanson explains, it doesn’t automatically mean that it can’t get food. There could be other causes. For example, toxic chemicals such as PCBs and other contaminants could be predisposing orcas to disease, making the animals too sick to eat.
Hanson thinks he saw an example of this last summer during much-publicized efforts to feed orca J50, known as Scarlet, since deceased. Scientists were trying to get J50 to eat a Chinook salmon injected with medicine, but “based on her behavior, I’m just not convinced that she was interested in eating anything. It’s just like people when they get sick, they are not necessarily interested in having something to eat.”
At least some southern resident orca’s prey range much closer to the heavily polluted urban waters near Seattle than their healthier counterparts, the northern resident orcas that also eat Chinook, possibly magnifying the effects of water-borne toxics. The small population could also mean serious genetic problems for the orcas, making them more susceptible to disease or other issues, Hanson says. In other cases, factors such as boat noise and disturbance could be interfering with the whales’ ability to find and catch prey.
“We’re continuing to proceed with the idea that increasing prey abundance is going to benefit the population,” Hanson says. “But the point is, you don’t die of being malnourished. If you die and you’re malnourished, it’s not the malnutrition that gets you. Unless it’s an extreme form which is essentially starvation, there may be some other factor that is related to a lower abundance of prey that is actually acting as sort of a tipping point.”
To date, no necropsy report for any southern resident orca has shown starvation as the cause of death, according to NOAA.
A lack of evidence?
Other scientists have made similar observations. “There are certainly a lot less Chinook than there were 100 years ago,” says University of Washington fisheries biologist Ray Hilborn. “It’s really since the ‘70s that the ocean conditions changed, and that the abundance [of salmon] dropped a fair amount. But is it the lack of Chinook that is the dominant problem? There’s really no evidence that that’s the case.”
There are plenty of benefits to protecting salmon, Hilborn says, but is a lack of salmon the cause of orca declines? He is not convinced. In fact, he argues, the small size of the southern resident orca population makes it difficult to say much that is definitive about the overall health of the whales.
“It’s always been a small population,” Hilborn says. You’re just dealing with a small population size. [The southern resident orcas] have periods of going up and down. There is just a lot of randomness when you’re dealing with dozens of animals — the kinds of randomness that in a population of 500 wouldn’t be noticeable. You can see a ten or fifteen percent downturn in a few years if you have a couple of deaths and no births.”
Hilborn chaired a 2012 review panel on the impacts of Chinook fishing on orca survival and says the findings from that panel remain relevant. In that report his group wrote: “There are insufficient data to relate the incidence of poor condition to nutritional stress caused by low Chinook salmon abundance or other causative factors. These data serve primarily to support the assertion that poor condition, which is clearly linked to increased risk of mortality, and by implication to fecundity, may reflect nutritional stress.”
Hilborn says that without what he and other scientists perceive as enough data, the causes of orca declines are inconclusive. He also makes the point that while some orcas are emaciated, there are other southern resident orcas that appear to be doing OK.
“You can look at the rest of the killer whales in the pod and they are looking fine. What is different about this individual? Does it have a disease? What is its problem? If the lack of Chinook was the issue, then why is this just sort of an individual here and there and not a population-wide phenomenon?” Hilborn says. “Clearly it’s much more complicated than that. It may have nothing to do with Chinook abundance. Or it may be that Chinook abundance is one of the thousand cuts that the southern residents are having to try to survive.”
A case for salmon
Not all scientists would agree with Hilborn’s assessment. University of Washington biology professor Sam Wasser calls Hilborn “overly cautious” in this case. “In my mind there’s really no question about it (that the orcas are suffering due to a lack of salmon),” he says. “There is an enormous amount of evidence here.”
Wasser and his colleagues published a 2017 paper showing connections between orca fecundity and nutritional stress (see our story in the Encyclopedia of Puget Sound, “Killer whale miscarriages linked to low food supply”), which Wasser says provides some of the evidence he mentions. The scientists looked at hormones from orca feces and presented a connection between a lack of food and high numbers of aborted pregnancies in southern residents.
“Low availability of Chinook salmon appears to be an important stressor among these fish-eating whales as well as a significant cause of late pregnancy failure,” the paper’s authors wrote.
In addition, low salmon runs may hurt orcas at nearly every turn, Wasser argues, magnifying stressors like underwater noise and disturbance. “The effects of vessel disturbance only come into play when the fish numbers get low,” Wasser says. Fewer food resources mean more energy spent for fewer returns, weakening orcas and potentially causing declines in immune systems that could lead to disease.
Wasser was one of several scientists who wrote a letter to the governor’s task force arguing that “increasing a wide variety of chinook salmon as quickly as possible must be the top priority for the Task Force and regional policymakers.”
Now, as the orcas decline further to a population of just 73 animals, Wasser continues his call to boost Chinook numbers. He sees the rarity of southern resident sightings in the Salish Sea this summer as a case for that argument. “It’s gotten so bad that for the first time known, the resident killer whales are rarely entering the Salish Sea because there are no Chinook for them to eat,” he wrote in an email.
Waiting for the orcas
Just why the orcas have been largely missing from the Salish Sea this summer remains an open question. Is it a lack of salmon? That is not a given, several scientists we spoke to cautioned, despite poor returns that have curtailed the Chinook fishery in the San Juan Islands this month. Orcas have entered the Salish Sea during poor salmon years before, and the presumed loss of three more members of the population during their journey outside of the Salish Sea only adds to the mystery. Did the orcas find a trove of salmon somewhere on their long journey? If so, why do they continue to die? Will they find what they need here in the Salish Sea? For now, no one knows for sure.