Blue Whale's Life History and Chemical Exposure Recorded in its Waxy Ears

You don't have to ask a whale to reveal its life history--just look at its earwax. Scientists have discovered that by analyzing the waxy buildup inside the ear of a deceased blue whale, they can figure out exactly how much exposure the animal has had to chemical pollutants over the course of its lifetime. The findings could be important for monitoring the health of whales in addition to the health of our oceans.

Over the course of their lifetimes, many baleen whale species continuously accumulate layers of wax in their ear canal. This, in turn, is sealed off from the external environment, forming an earplug that remains in place over the course of a whale's life. In fact, scientists can use this wax to tell the age of a deceased whale since the layers form distinct layers, similar to tree rings.

Yet if this wax could be used to indicate a whale's age, couldn't it also record other valuable information? That's what the researchers set to find out. They believed that it was possible that the waxy layers would contain a chronological archive of the fat-soluble chemicals that a whale naturally secrets and is exposed to in the ocean. In order to test this idea, they analyzed the chemicals within each layer of an earplug from a deceased male blue whale.

"You have this 100-year-old question: How are we impacting these animals?" asked Sascha Usenko, one of the researchers, in an interview with Wired. "There is ship traffic, environmental noise, climate change and contaminants. Now, we are able to provide definitive answers by analyzing whale earwax plugs."

So what did they find? It turns out that they discovered fluctuating levels of testosterone and the stress hormone cortisol during the whale's 12-year lifespan. They also found persistent organic pollutants, such as pesticides and flame retardants within the first year of the whale's life. The whale probably accumulated these during the time it was nursing. That's not all they found, though. They also found a spike in the levels of mercury present during two distinct time periods in the whale's life.

The findings could allow researchers to better assess what pollutants might be affecting whales. In addition, the technique could also be used to investigate a blue whale's sexual maturity and life events.

The findings are published in the journal Proceedings of the National Academy of Sciences.