Scientists have uncovered details about the life of a blue whale that died in 2007, by analyzing his earwax.

“It’s like keeping a diary for us,” said Stephen Trumble, a biologist at Baylor University in Waco, Texas, in an interview with As It Happens this week.

Researchers have long determined the age of a dead whale by examining its earplug – a long piece of wax that accumulates in a whale’s ear over its lifetime.

“Typically, it looks like kind of a beat-up candle,” Trumble told As It Happens host Carol Off.

The wax is brown and “it definitely smells,” he added.

When Sascha Usenko, a colleague of Trumble’s who is an analytical chemist, learned that earplugs were used to tell a whale’s age, he suspected there might be chemicals inside that could be analyzed over the whale’s lifetime.

He and Trumble managed to get a foot-long earplug from a blue whale that had been killed in a collision with a ship off the coast of California in 2007.

The earplug revealed that the whale was about 12 years and six months old when he died.

The chemical analysis of the earplug showed that the whale received a large load of organic pollutants — about a fifth of its lifetime exposure — from its mother during its first year, either while in the womb, while nursing or both. Its testosterone levels peaked at age nine, suggesting that was when it reached sexual maturity. Previously, scientists weren’t sure when whales were old enough to breed.

Record of stress

The whale’s levels of the stress hormone cortisol peaked when the whale was around 10 years old, suggesting that the most stressful events in the whale’s life related to competition for a mate or social bonds formed around the time of sexual maturity.

The study found a variety of contaminants in the whale’s earplug, including flame retardants, which were not found in the earplug of a whale who died in 1969, before flame retardants were widely used.

Previously, scientists had relied on analysis of whale blubber to measure their exposure to pollutants, but that provides information about only short periods of time.

The findings suggest that whale earwax can be used as a new method to profile both hormone levels and chemical exposure over a whale’s entire lifetime — up to 80 years.