Researchers are learning a lot about the lives of orcas from their deaths, thanks to a team of experts from British Columbia and the United States.
Though killer whale carcasses are on occasion found washed up on beaches around the North Pacific, few tests were being done to figure out why or how.
The lack of information became a real concern when researchers noticed an alarming drop in the 1990s in the population of southern resident killer whales found around southern Vancouver Island and as far south as California. They declined about 20 per cent in a decade, dropping to about 78 individuals.
"This raised quite a bit of concern," said Stephen Raverty, of the B.C. government's Marine Ecosystem Health Network.
"We were very interested in trying to place this in context of whether it was something that was occurring just regionally, or whether it would have broader ramifications for the populations along the western seaboard … and up into the eastern Pacific as well."
So Dr. Raverty and Joseph Gaydos, of the University of California Davis' SeaDoc Society, thought a checklist of sorts for whale necropsies could garner helpful information.
That list was distributed from Russia to Japan, Alaska to Mexico, almost a decade ago.
They have now published their first study of the information gathered. The study, in the journal Marine Mammal Science, looks at tests from 371 stranded whales dating as far back as 1925.
The tests have opened a window into whale behaviour, including migration patterns revealed by looking at when and where the orca carcasses have washed ashore.
For example, winter ice has traditionally prevented whales from accessing areas in Alaska where they're easily observed, but that's changing.
"With climate change, we know that there are increasing numbers of killer whales that are being spotted in the Arctic and certainly there is a lot of interest in terms of looking at these animals and changes that may be associated with mortality up there, related to climate change, environmental changes and so on," Dr. Raverty said.
Because of the protocol developed by Dr. Raverty and Dr. Gaydos in 2004, there have now been necropsies performed on dozens of animals.
In the coming months, Dr. Raverty, a veterinary pathologist with the B.C. Ministry of Agriculture and Lands, and his colleagues will examine test results more closely, looking for information about diseases, contaminants and other factors that may be affecting the whales.
"The whales themselves are really icons of the Pacific Northwest. They're highly valued by the public, they're very intimately associated with the natural history and the folklore of our First Nations communities," Dr. Raverty said.
"And because they are so long-lived, and high in the food web, they're also a very good sentinel of ecosystem health."
Dr. Gaydos said the study is providing key information about not just whale, but ocean health.
"What we want to do, as far as helping killer whales, those species or subpopulations that are in danger, we want to know about their diseases so we can take those into account when we plan recovery strategies," he said.
"It gives us important information for continuing surveillance efforts."
The necropsies have shown that the orcas absorb extremely high loads of man-made toxins, suffer from infectious diseases and, in the case of fish-eating populations, depend primarily on severely depleted salmon stocks.
The response from throughout the Pacific, from Russia to Mexico, has been incredible, he said.
The necropsy list has increased data collection. Over the last two decades, an average of 10 killer whales a year have been discovered stranded across the entire North Pacific Ocean, and necropsies have jumped from about one in 50 to one in three.
"Because killer whales are apex predators and flagship conservation species, strandings are sad events," he said. "But this study confirms that if we make every effort to understand why the strandings occurred, we will ultimately improve the fate of the species."
There has also been an increase in funding for southern resident killer whale recovery from both the U.S. National Marine Fisheries Service and Canadian Department of Fisheries and Oceans.