The furies of war and the perils of climate change perpetuate stress, and not only in humans. Just check whale earwax, Baylor University researchers say.
The new study found that whales have been stressed for nearly 150 years, based on the determination of cortisol, a stress-induced hormone, located in thick earplugs of wax.
Five years ago, Stephen Trumble and Sascha Usenko discovered that analyses of whale earwax can determine a lifetime’s worth of hormone and chemical exposure in the marine mammals. The finding represented advancement from decades of whale research, which was mostly based on examinations of whale blubber.
The duo’s latest work linked high cortisol levels to dangerous periods for whales: World War II in the 1940s, the height of the whaling industry in the 1960s, and a dramatic rise in sea temperatures in the 1990s.
“The stress hormones were probably the more indicative of anything that’s going on,” said Trumble, an associate professor of biology. “We always get stress hormones. If we can figure out the response of the animal, and then we look at what’s involved with this response, we get some sort of a clue what’s going on. … The cool thing was we put all these stress hormones together and kind of made a profile over time.”
Naval battles with ships and submarines during World II likely caused an increase in whale stress levels in the 1940s, the study found, and stress brought on by whaling activity continued until the 1970s, when international agreements began to curtail whale hunts.
Trumble said year-to-year whaling data matched well alongside what he and his colleagues were finding in the earplugs. And the effects of global warming on whales could include a changing diet, or any number of factors.
“There is something there,” Trumble said. “This is what we’re going to build on.”
Their research of whale earplugs started almost 10 years ago, when they wondered if earplugs could be used to determine age and other characteristics. The Smithsonian Institution was ready to dispose of about 1,000 earplugs before Trumble inquired about them.
Similar to tree rings, whale earplug layers are used to age whales, which can span decades. For example, gray whales are believed to have a typical lifespan of 40 to 80 years.
“We take a photo pretty close up, mess around with contrast and brightness, and I just try to make those layers come out as much as possible,” said Dani Crain, a graduate student in the biology department. “I age it before I start cutting the layers apart.”
The research into whale earwax is set to continue under the direction of the Baylor professors who first highlighted its significance.
“(The earplugs) literally went from being thrown away, now they’re the objects of wonder at the Smithsonian,” Trumble said.