For whales, stress starts in stomach
Jun 07 2012
A hungry killer whale is a stressed killer whale, a study that analyzes hormone levels in whale poop has found.
The paper, published Wednesday in the journal PLoS ONE, looked at the scat of endangered southern resident killer whales, which swim around Vancouver Island and Puget Sound, and concluded that lack of chinook salmon is the major stressor.
Not having sufficient chinook is more stressful than coping with boatloads of whale-watchers, said lead author Katherine Ayres, an environmental consultant who conducted the research as a biology doctoral student at the University of Washington.
"In lean times, however, the stress level normally associated with boats becomes more pronounced, further underscoring the importance of having enough prey," Ayres said.
Killer whale recovery strategies in the U.S. and Canada have identified food supply, noise from boats and toxins as major problems faced by the whales. There are about 83 whales in the three resident pods.
Most whale poop samples for the study were collected with the help of Tucker, a specially trained black Labrador who stands on alert in a small boat and signals to his handlers when he recognizes the fishy smell of whale scat.
"This is the first study using scat-detection dogs to locate killer whale feces," Ayres said.
Whales are always difficult subjects to study because the animals spend 90 per cent of their time underwater, she said.
The program was developed by Samuel Wasser, a University of Washington biology professor, who also uses dogs to find animal scat for land-based studies.
The poop detected by Tucker's nose provides invaluable information that could not be obtained by more invasive methods of testing hormone levels, such as tissue samples, Wasser said.
The researchers looked at levels of glucocorticoids, which are released when animals face immediate challenges, and the thyroid hormone, which changes the metabolism depending on how much food is available.
It was found that nutrition was the driver that regulated reactions to other stresses such as whale-watching boats, Wasser said.
"If there's something to fix first, it's the fish," he said.
That could mean changing the chinook fishery, as the whales prefer chinook to other salmon, but other pressures on chinook populations include habitat loss and dams on U.S. rivers, Wasser said.
"We need to look at structures obstructing fish passage and how much hatchery fish are impacting the situation," he said.
A surprising finding in the study is that the whales are best fed when they come into the Salish Sea in late spring, Wasser said.
It's likely they are feeding heavily on spring chinook runs, probably in areas such as the Columbia River, meaning special attention must be paid to those runs, he said.