Whales record major life events in their earwax

Who needs a diary when you’ve got whale earwax? Hormone peaks, ocean pollutants, stress levels – it’s all there.

The plugs, which can weigh 250 grams and be 25 centimetres long, reflect annual migration patterns. During a blue whale’s six-month feeding season, earwax is light-coloured, filled with fat from its rich diet. As it fasts during migration, a darker layer forms. These layers allow scientists to age whales when they’re found dead.

Now, for the first time researchers have used the earwax to study a whale’s exposure to ocean contaminants from birth to death. “This has opened the floodgates for doing some great analysis,” says Sascha Usenko of Baylor University, Waco, Texas. “Now we can look at the impact of ocean contaminants on these organisms historically, which has always been very hard to address.”

Usenko and Stephen Trumble, also at Baylor University, shaved away at a plug from a 12-year-old male blue whale that was killed in a 2007 boating accident off the coast of California. The layers contained varying concentrations of DDT and flame-retardants. Exposure was highest during its first year, probably while the whale was nursing.

The plug also contained traces of hormones, which are broken down by the body and don’t leave records elsewhere. Testosterone levels peaked at 10 years, marking the beginning of sexual maturity, which can be difficult to determine but is important for conservation efforts. And levels of the stress hormone cortisol increased over the whale’s life, possibly because finding food, migrating and mating all got harder.

Usenko says the earwax method means we can look at how exposure to chemicals in the environment alters a whale’s stress levels, and how exposure today is different from exposure say, 50 years ago.

Journal reference here.