Whales are stressed out by climate change, and it shows in their earwax

Enlarge / A whale earplug, showing the layers accumulated across a lifetime, and the corresponding cortisol levels. (credit: Nature Communications)
In a whale’s earwax lie clues to its entire life. Some species of whale build up large “earplugs” of fatty, waxy material that can trap hints about the hormones that coursed through the beast and the pollutants it swam through.
In a paper published this month in Nature Communications, researchers used earplugs recovered from 20 whales to explore how their stress levels have responded to changes over the last 200 years. They found that the whales’ stress levels moved in concert with being hunted, rising as whaling levels reached fever pitch and plummeting as whaling levels decreased. But since the 1970s, stress levels have been steadily climbing again, keeping step with warming ocean waters.
The ear is the window to a whale’s soul
Tracking even the most obvious behaviors in wild animals can be a tricky business—for instance, nobody knows for sure where great white sharks go to breed. Even knowing how many animals there are in a population can be difficult. Figuring out how stressed whales have been is a near-impossible task but a crucial one: stress affects the health of individual whales, which in turn affects the health of the population. So tracking stress levels could be useful for developing a comprehensive whale conservation strategy.
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