In earwax, the tale of a whale

Researchers have reconstructed the lifespan of a male blue whale, including its brushes with both environmental pollutants and female blue whales, using its earwax.

Whales have earwax, and it's useful.

Researchers have reconstructed the lifespan of a male blue whale, including its brushes with both environmental pollutants and female blue whales, using the lipids and waxes that plug its ear canal. The new technique gives marine researchers another tool with which to portrait a whale’s lifetime, allowing scientists to chronicle which hormones the mammal released and which chemicals it absorbed – and when it did so.

“This type of data is really, really rare,” says Sascha Usenko, a professor at Baylor University and a co-author on the paper, published in the journal Proceedings of the National Academy of Sciences. “This is a new opportunity to ask a lot more questions.”

Blue whales are big. To be exact about it, the blue whale, at up to 100 feet long and 300,000 pounds,is the biggest animal ever to grace this planet. Charmingly, their hearts are proportional: a blue whale’s heart weighs about 1,300 lbs. Their brains, though, are not, at just 16 lbs. 

To get to this size (brain not included), blue whale calves need to grow about 250 lbs each day, or 10 lbs an hour, which requires a daily helping of about 500 gallons of its mother’s milk. At full size, the blue whale must eat about four tons of krill (a shrimp-like animal, but saltier-tasting), per day, to sustain its tremendous bulk. Since the blue whale is toothless, its mouth is instead fringed with lots and lots of baleen, a keratin-based bristle, which separates the krill from the water when the whale takes an ocean gulp, pushing the water out and the millions and millions of unfortunate crustaceans in.

But for all that is known about the long, big lives of blue whales, which live to be around 80 to 90-years-old, more is still unknown. While it has long been thought that whales feel the effects of human activities, including waste dumping and noise pollution, the biographies so far collected from whales have been isolated chapters, told in samples of the animal’s blood, feces, and blubber. Little is also known about the whale’s hormone levels during its development.

The idea of using earwax to fill in those knowledge gaps arose out of two facts, says Dr. Usenko. The first was that most baleen whales, from birth to death, accumulate layers of what is known as cerumen, better known to us as earwax, in their ear canal. That earwax is composed of alternating light and dark-colored layers, which are associated with periods of food bounty and austerity. Much as a fish’s ear bones record a tale of summer and winter feeding that can be used to confirm its age, the waxy layers provide an estimate of the mammal’s age, which each layer translating to about 6 months of time, based on whale migration patterns.

The second fact was that fat is a reliable repository of hormones and contaminants; at the moment, whale blubber samples are sometimes used to gauge which chemicals the animal has absorbed. And since earwax is lipid-rich, it too would be packed with the pollutants to which the animal had been exposed and the hormones it had pumped throughout its bloodstream.

So, if those two facts were combined, could earwax be used to timestamp the various chemical and hormonal levels that the animal had experienced throughout its lifetime? Could earwax tell a long song of the whale?

To find out, researchers analyzed a 25.4-cm earplug from a 12-year-old male blue whale that had been killed in 2007 near Santa Barbara, Calif., when it collided with a ship.

Using the hardened wax, the whale’s testosterone levels were found to have peaked at about 10 years old, a 400-fold increase from baseline levels. Just after that, at about 10.5 years old, the whale’s cortisol levels reached their maximum, at a 9-fold increase from baseline levels. Since rising amounts of cortisol suggest stress in mammals, the researchers suggested that the peaking levels might be concurrent with time that the male began competing for a mate, dealing with the pressure of appealing to girl whales.

“The social dynamic has changed,” says Usenko. “Anyone who has been through this period in life would recognize this.”

The earwax also recorded pollutants accumulated during the animal’s lifetime, including two spikes in the whale’s mercury levels, when it was about five and then 10 years old. The sudden spikes were likely associated with environmental events near California, the scientists reported.

About 20 percent of the whale’s lifetime contaminants also came from its mother, during gestation or lactation, the researchers found. That find was another confirmation of previous research showing that sizable amounts of pollutants are passed from female mammals to their children, says Usenko.

At the moment, it’s not possible to tease out which of the hormonal changes are natural and which are anthropogenic, says Usenko. For example, the rising cortisol levels in the sampled whale could be related to human-caused stress factors, such as close encounters with ships, instead of close encounters with female whales. Determining what is a natural hormonal shift, versus what is a human-caused stress, would require comparing the whale’s data with data from other whales, especially whales alive before pollutants had saturated the Californian waters, he said.

Even then, different whales manifest different hormonal levels, so comparisons would be difficult, he said.

Still, despite the limitations, the researchers said the earwax-based technique could underpin new research about how humans influence the underwater lives of whales: “We anticipate that this technique will fundamentally transform our ability to assess human impact on these environmental sentinels and their ecosystems,” the authors wrote.

Blue whales are classified as endangered, with just 8,000 left in the world after humans invented the harpoon and started going after something 30,000 times their size. About 2,800 of those animals live near California. Right now, the best chance people have of seeing a blue whale is in all likelihood at the Natural History Museum in New York, where an elegant, 94-foot-long, 21,000-lb. fiberglass version is suspended from the marine wing’s ocean-high ceiling.