How do you get to know one of Earth’s most mysterious creatures? By looking at its earwax, according to a group of US researchers. Analysing the contents of blue whales’ ears, through a process similar to analysis of tree rings, led the team to construct a chemical timeline of the its life. This technique, they say, should allow significant further research both into how blue whales develop and how they respond to environmental concerns.

The earplug of a whale is the lifetime accumulation of its earwax. It slowly builds up in layers. As such, the earplug, like tree trunks, can be used to estimate a whale’s age. The earplugs have been used for this purpose for a while, but Stephen Trumble, assistant professor of Biology at Baylor University, and colleagues realised that a lump of wax, which in this case was 25cm long, possesses a lot more secrets than just the age.

Stephen Trumble / Baylor University

“We were the first group to see that the earplug of a blue whale contains a lot more information,” Trumble said. “We realised that if we chemically analysed one, we could create a chemical portrait of the whale’s life.”

There are no other animals whose lifetime chemical profiles can be drawn. “Large baleen whale species, such as the blue whale, are the only wild animals that we can do such a thing,” Trumble explained. “The only other situation where constructing a lifetime chemical profile is possible would be by constantly taking samples from an animal in captivity.”

Trumble’s team analysed the earplug for a wide range of hormones and pollutants including the stress hormone cortisol, the developmental hormone testosterone, organic contaminants such as pesticides and flame retardants, and other pollutants such as mercury.

Currently analysis of whale blubber is used in order to assess chemical levels. But all that this allows one to find out is what chemicals the whale absorbed. The unique treelike composition of the earplug means that hormone and pollutant levels can now be mapped over the length of the blue whale’s life. “Our technique allows you to discover when, not just if, chemicals have been absorbed,” Trumble said. “The chemical tracing means that you can reconstruct time periods.”

The method allowed Trumble and colleagues to construct a developmental profile for the whale. Testosterone profiles, for example, suggest this male blue whale reached sexual maturity at approximately ten years of age, which corresponds well with and improves on previous estimates. They also found that stress levels doubled over the whale’s lifetime. This could allow for a more comprehensive examination of stress levels - in response to rising ship traffic and environmental noise, for example.

Stephen Trumble / Baylor University

Because the lipids, waxes and keratin that form the earplug also work as a sink for pollutants - such as pesticides polychlorinated biphenyls (PCBs), polybrominated diphenyl ethers (PBDEs) - a chemical portrait of the whale’s exposure to contaminants could also be constructed. “The technique allows us to go back in time and see when the animal was exposed to certain things, and how the animal reacted to exposure,” Trumble said. This promises the possibility of improving our assessment of the effects of contaminant use and emission in the oceans.

Luke Rendell, lecturer in biology at the University of St Andrews, finds the research fascinating. “It will allow us to learn a little bit more about the animals, something that is especially important due to their being endangered,” he said. “Documenting how chemicals are work their way through ecosystems is invaluable.”

How much can be asserted from the current analysis is limited, of course, as only one whale has so far been profiled. But the success of the process promises greater future prospects. The analysis can take on a historic perspective, too - as there are archives of earplugs harvested from whales involved in shipwrecks that reach back to 1969. A map and a timeline of whale activity and marine pollution over the last 50 years can now be drawn up. This means better assessment of the effects that human activity is having, and will have, on the environment, oceans and these beautiful giant creatures.