Baleen whale cortisol levels reveal a physiological response to 20th century whaling

Abstract: One of the most important challenges researchers and managers confront in conservation ecology is predicting a population’s response to sub-lethal stressors. Such predictions have been particularly elusive when assessing responses of large marine mammals to past anthropogenic pressures. Recently developed techniques involving baleen whale earplugs combine age estimates with cortisol measurements to assess spatial and temporal stress/stressor relationships. Here we show a relationship between baseline-corrected cortisol levels and corresponding whaling counts of fin, humpback, and blue whales in the Northern Hemisphere spanning the 20th century. We also model the impact of alternative demographic and environmental factors and determine that increased anomalies of sea surface temperature over a 46-year mean (1970-2016) were positively associated with cortisol levels. While industrial whaling can deplete populations by direct harvest, our data underscore a widespread stress response in baleen whales that is peripheral to whaling activities but associated with other anthropogenic change.

In the news:
1. Baylor University: ‘‘Baylor Professors Use Whale Earwax to Reconstruct Whale Stress Levels Spanning More Than a Century’’
2. Natural History Museum - London: ‘‘Whale earwax reveals just how much human activity can stress out marine mammals’’
3. Natural History Museum - London Video: What can we learn from whales' earplugs?
4. National Geographic: ‘‘Earwax reveals how humans have changed whales’ lives’’
5. ARS Technica: ‘‘Whales are stressed out by climate change, and it shows in their earwax’’
6. Smithsonian Magazine: ‘‘We Know How Stressed Whales Are Because Scientists Looked At Their Earwax’’
7. The Atlantic: ‘‘The History of the Oceans Is Locked in Whale Earwax’’