Almost everything about blue whales is big, except their pinhole ears. And I know it’s early in the story, but, fair warning, this is where things get kind of gross: Because of those tiny ears, whales don’t have any good way to get rid of their earwax.
The wax—scientists call it cerumen, which sounds so much nicer—just builds up over an animal’s entire lifetime. It forms a stick like a crayon or a candle, but waxy, roughed up, fibrous, with a familiar yellow-brown coloration. “It’s not really appealing,” is the understated way Stephen Trumble, a marine mammal physiologist at Baylor University, puts it.
A few years ago, Trumble and a colleague were chatting about whale earwax while strolling across campus to the coffee shop. Trumble mentioned that biologists sometimes use the lamina, or layers, in these earplugs to age a whale, and a light blinked on in Sascha Usenko’s head. “Earplugs?” he said.
Usenko, an environmental chemist, had been analyzing sediment cores to construct a modern history of pollution in various national parks in the American West. Maybe, he wondered aloud, they could try the same thing on a whale’s earplug?
They phoned Michelle Berman at the Santa Barbara Museum of Natural History to ask if she happened to have a whale’s earplug handy. By good luck—and this is the sort of thing that makes science so wonderful—she replied, “I have one in my freezer. It may take me a while to find it.”
The result is a paper being published today in the Proceedings of the National Academy of Sciences. It turns out that earwax is good not just for aging whales, but also for reconstructing their entire life histories.
The earplug Trumble, Usenko, and their co-authors studied came from a 65-foot-long male blue whale killed by a ship strike near Santa Barbara in 2007. The earplug itself was 10 inches long, with 24 layers, indicating an age of about 12 years, plus or minus six months.
By studying the changing levels of testosterone and cortisol over time, the researchers were able to determine that the whale reached maturity at about 10 years. As with any human teenager, social and sexual competition kicked in at that point, and the stress hormone cortisol surged.
Chemical analysis also revealed the presence of DDT and PCBs, both banned in the United States in the 1970s, along with flame-retardants, mercury, and other pollutants. Much of this contaminant load got passed down by the whale’s mother during pregnancy and nursing, as also happens in humans. But the mercury came later, perhaps as the whale migrated up and down the California coast. “There’s still a lot of mercury used in gold mining,” says Trumble, and some may get washed out to the sea in heavy rains.
Earwax isn’t the only way to detect these contaminants. You can also do it with whale blubber, says Usenko. But the earwax allows toxicologists for the first time to know exactly when the exposure occurred and, particularly with mercury, how it might have affected the whale’s development. “You can’t get this type of data for any other animal on the Earth,” he says, “unless you have a catheter in a lion and you’re following it around the Sergeneti. It’s pretty rare to get a lifetime profile of an animal.”
The new technique also enables researchers to get that data without the expense of going to sea, and without risk of disturbing living animals in an endangered species that is only beginning to recover from the era of commercial hunting. It’s now also possible to look at changes over time, because natural history museums have been collecting earwax plugs from whales for decades. The next project for Trumble and Usenko is to analyze a half-pound “beast” of an earplug from a female bowhead whale that died in 1964.
The research raises one final question: Why do whales produce and apparently hear such haunting underwater music, if their heads are packed full of earwax? Not surprisingly, their ears aren’t much good for hearing, the scientists say. Instead, whales mainly pick up vibrations via their jawbones.