U. WASHINGTON (US) — Not having enough Chinook salmon to eat stresses out killer whales in the Pacific Northwest more than having boatloads of whale watchers nearby, according to hormone levels of whales summering in the Salish Sea.
In lean times, however, the stress level normally associated with boats becomes more pronounced, further underscoring the importance of having enough prey, says Katherine Ayres, an environmental and pet-behavior consultant who led the research as a University of Washington doctoral student in biology.
In a surprise finding of the study, published in the journal PLoS One, hormone levels show that southern resident killer whales are best fed when they come into the Salish Sea in the late spring, an area that includes Puget Sound and the straits of Georgia, Haro, and Juan de Fuca. Once there they get a necessary boost later in the summer while eating Chinook salmon at the height of the Fraser River run.
Even a mile away, Tucker, a black Lab, can pick up on the scent he’s been trained to recognize as the fishy smell distinctive to southern resident killer whales, a group of orcas listed as endangered by both Canada and U.S. (Credits: Ken Balcomb, Jeanne Hyde)
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While Fraser River Chinook are an important food source, helping the southern resident killer whales may mean giving additional consideration to spring runs of Chinook salmon off the mouth of the Columbia River and other salmon runs off the West Coast, if that’s where the orcas are bulking up in the spring, Ayres says. “Resident” killer whales are fish-eating orcas, unlike the so-called “transient” orcas that eat marine mammals.
For the study, scientists analyzed hormonal responses to stress that were measurable in whale scat, or poop. Many samples were collected using a black Labrador named Tucker on board a small boat in the vicinity of individuals or groups of whales. Even a mile away, Tucker can pick up on the scent he’s been trained to recognize as the fishy smell distinctive to southern resident killer whales, a group of orcas listed as endangered by both Canada and U.S.
“This is the first study using scat-detection dogs to locate killer whale feces,” Ayres says. “The technique could be used to collect scat and study stress in other species of whales, always difficult subjects to study because the animals spend 90 percent of their time underwater.”
Since the population of southern resident killer whales declined nearly 20 percent between 1995 and 2001, scientists and managers have wondered if the animals weren’t thriving because of lack of food, the closeness of boats, toxins built up in their bodies or a combination of all three.
“Behavior is hard to interpret, physiology is easier,” says co-author Samuel Wasser, professor of biology and developer of the program using dogs like Tucker to detect scat for biological research. “Fish matter most to the southern resident killer whales. Even if boats are important to consider, the way you minimize that impact is to keep the fish levels high.”
It’s the same with toxins, Wasser says. The new study specifically considered stress caused by inadequate prey and boats. But toxins accumulating in body fat will likely affect killer whales most when food is scarce and they start to use that stored fat, releasing toxins into their bodies when their physical condition already is in decline. When whales are well-fed, toxins should be less of a factor.
“We assume winter is a lean time, so to come into the Salish Sea at their nutritional high for the year, then clearly they have been eating something—a very rich food source—before they arrive,” Wasser says. “It appears another fish run is critical to them before they get here.”
Some evidence points to the Chinook returning to the Columbia River, although Wasser says more spring data are needed.
“To support a healthy population of southern residents we may need more salmon than simply the number of fish being caught by commercial and sport fishers,” Ayres says. “We may need to open up historical habitats to boost wild salmon, such as what is being done with the Elwha River and what is proposed for the Klamath River. That may be the only way to support the historic population size of southern residents, which is ultimately the goal of recovery.”
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