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Prey Shortage Threatens Killer Whales, Study Aided By Scat-detection Dog

June 8, 2012
Image Caption: Katherine Ayres handles Tucker as he zeros in on the scent of whale poop. Tucker never goes into the water, he just leans over the bow in the direction the boat should travel. Credit: Jeanne Hyde

Southern dwelling killer whales, located in the Pacific Northwest, experience more strain by lack of fish than by hordes of whale watchers, according to a study conducted in the Salish Sea. Chinook salmon, a staple for the killer whales of that area, are dwindling in number and this effects the whale population heavily.

Published on June 6, 2012 in the online journal PLoS ONE, the study, led by environmental and pet-behavior consultant Katherine Ayers, focused on the glucocorticoid and fecal thyroid levels of the whales. Both hormone levels suggest that lack of prey is the main cause of stress.

Ayers, who completed the study while seeking a doctorate in Biology at the University of Washington, asserted that in times when food resources are thin, increased stress levels due to boats depend on fish abundance, indicating that the main source of stress is directly related to a lack of nourishment.

Ayres states, “The data support Chinook salmon being a more important driver of physiology than vessel traffic for the Southern resident killer whale population, however vessel traffic may cause added physiological stress during times of low prey availability.”

Fellow researcher Samuel Wasser agrees, stating, “Recovering their Chinook salmon prey is critical to assure long-term killer whale recovery. Everything, including boats and toxins, matters more when prey is low.”

Researchers examined hormone levels by collecting many samples of whale scat, or feces. A surprising member of the team, a black Labrador named Tucker who is able to catch a scent from a mile away, located the samples by sniffing out the distinct, fishy odor of the southern killer whale scat.

“This is the first study using scat-detection dogs to locate killer whale feces,” stated Ayres. “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.”

“Behavior is hard to interpret, physiology is easier,” stated Wasser, who created the program where dogs like Tucker are used to locate whale scat. “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.”

According to Ayers, the hormone levels in the southern dwelling killer whales, “Endangered” orcas in both the US and Canada, show that they forage best during the late spring within the Salish Sea. This area includes the Strait of Georgia, Puget Sound, and Haro and Juan de Fuca. During the late summer, the whales get an enhancement in nutrients from Chinook salmon when the Fraser River run reaches its peak.

“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,” co-author of the study and UW professor of Biology Samuel Wasser stated. “It appears another fish run is critical to them before they get here.” He also stated, “Some evidence points to the Chinook returning to the Columbia River, although Wasser said that more spring data are needed.”

The decline in southern resident killer whale populations, nearly twenty percent between the years of 1995 and 2001, triggered scientists and managers to consider the root of the decrease, whether it was toxins built up in the whale´s bodies, a lack of food resources, the proximity of vessels, or a mixture of all three.

In order to pinpoint the cause of the population decline, researchers studied two types of hormones. According to Ayers, whales release glucocorticoids when experiencing times of stress such as in food shortages or in fight-or-flight occurrences. Instead of spiking when large numbers of boats encircled the killer whales, their glucocorticoid levels decreased because of the abundance of Chinook salmon in the area at that time.

“The other hormone, thyroid hormone, tunes metabolism depending on how much food is available, for example ramping down metabolism to lower the energy an organism expends when food is scarce.” Ayres stated.

In contrast to the more immediately effected glucocorticoids, thyroid hormone levels do not raise or fall due to boat traffic. During the summer of the five-month period when the whales remained in the Salish Sea, their thyroid hormone levels fell as they awaited the arrival of the Chinook salmon run. Once the fish arrived, the hormone levels increased, only to decrease once more when the run was over.

Following a draft report published by the U.S. and Canadian fisheries experts on May 3, 2012 pertaining to the effect of salmon fishing on the southern resident killer whales, the PLoS ONE paper co-author Samuel Wasser said that the report did not focus enough on the year-to-year salmon inconsistency. However, Wasser did agree that the report adequately expressed that more information is necessary on the wintering and early spring habits of the killer whales.

Currently, Chinook salmon stocks are harvested at a rate of approximately twenty percent, “so there is limited potential for increasing Chinook abundance by reducing fishing pressure,” according to the earlier report. Wasser stated, “More extreme measures may be required that increase overall Chinook salmon stocks.”

“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 stated. “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.”

Other co-authors are Rebecca Booth of the UW; Jennifer Hempelmann, Candice Emmons, M. Bradley Hanson and Michael Ford of the National Oceanic and Atmospheric Administration’s Northwest Fisheries Science Center; Kari Koski of Soundwatch Boater Education Program and the Whale Museum, Friday Harbor; Robin Baird of Cascadia Research Collective, Olympia; and Kelley Balcomb-Bartok, who helped get the study off the ground through collaboration with the Center for Whale Research.

The work was funded by Washington Sea Grant based at the UW, NOAA’s Northwest Fisheries Science Center, Northwest Scientific Association, UW Department of Biology and the Canadian Consulate General.


Source: redOrbit Staff & Wire Reports



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