Earwax reveals how humans have changed whales’ lives

Luckily, museum curators around the world have had the good sense to hold onto massive plugs of earwax pulled from dead whales over the centuries.Thanks to those plugs, scientists have now discovered a record, hidden in earwax, of how human activities have stressed out whales over the past century and a half. Stephen Trumble, a comparative physiologist at Baylor University, and his colleagues published the findings this month in Nature Communications.It turns out we’re incredibly stress-inducing—from whaling to war to climate change, our actions have been affecting whales, even if we don’t interact with them directly.In the new study, hormone profiles from 20 fin, humpback, and blue whales revealed a tight connection between whaling activities and stress from the late 19th century to the 1970s, when legislation dramatically reduced the hunting of whales.Hunting wasn’t the only source of stress that the researchers saw, either. From 1939 to 1945, elevated cortisol levels indicated that the whales’ stress levels were high, even though fewer whales were being harpooned. But there was another stressor at the time: global war. “We suspect this increase in cortisol during World War II is probably a result of noise from planes, bombs, ships, et cetera,” says Trumble.After about 1970—and especially after 1990— the researchers saw a worrying trend: Cortisol levels also increased rapidly alongside rising water temperatures. This suggests that climate change, too, is stressing the whales.