If you think extracting globs of earwax from your own ear is gross, imagine handling a nearly foot-long, inch-thick tube of whale earwax.
To protect delicate eardrums, around 8 to 10 baleen whale species have ear canals that are naturally sealed off from the external environment. Over the years, earwax begins to build in the narrow tubes. Whales don’t hear like humans–fat deposits in their jaw funnel low-frequency sound vibrations toward their eardrum, so the wax does not get in the way of their hearing.
By the end of a blue whale’s life, the wax forms a solid, permanent tube of what researchers refer to as an earplug in the animal’s ear canal. While most people would likely consider the prospect of handling this stuff rather off-putting, for scientists the earwax provides “unprecedented lifetime profile” of the animal, according to a new paper published in Proceedings of the National Academy of Sciences.
Like tree rings, layers found within whale earplugs are already used to help researchers estimate an animal’s age. In this new study, scientists guessed that the wax may have more secrets to tell.
Traces of events recorded from birth to death may leave their mark in the whale’s ear wax, they figured. Chemical pollutants, for example, are a problem for ocean creatures, included endangered blue whales. Many of these contaminants build up in whales’ fatty tissues, but fat offers no clues as to when a whale might have been exposed to those chemicals. Perhaps the earplug would.
However, testing this hypothesis requires invasively getting at that golden substance–a difficult task while the whale is alive. But in 2007, a 12-year-old, 70-foot long blue whale washed ashore near Santa Barbara, dead from a ship strike. The recovered 10-inch long earplug sat in a freezer for a couple years, until the team sampled it. They also took samples of its blubber to compare it with the wax and get chemical profiles of these two lipid-rich materials’.
Earwax is continuously deposited throughout the whale’s lifetime, but forms alternating light and dark layers on approximately 6 month intervals. The light corresponds to periods in the whale’s lifecycle when it’s feeding, while the dark represents times of fasting and migration. The team performed numerous chemical analyses to produce a profile of the whale’s life, told at a 6-month resolution.
Within the wax, they found markers of the stress hormone cortisol, growth-inducing testosterone, contaminants such as pesticides and flame retardants, and mercury. Much like humans, this particular whale’s stress levels increased as it got older, effectively doubling over its lifetime. Testosterone peaked when the whale was about 10 years old–the height of puberty for male blue whales.
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