The endangered blue whale species could be saved by its ear wax, according to new research.

Throughout their lives, blue whales accumulate layers of wax in the ear canal that form a plug, almost a foot long, and which remain permanently in place until they die.

Scientists from Texas have analysed these layers, in a manner similar to tree rings, to roughly estimate a specific whale’s age, track changes in its hormone levels, and see which chemicals it was exposed to in the ocean.

This wax can also be used by researchers to work out what needs to be done to protect them from stress, pollution and other threats in the future.

The blue whale is the largest animal on Earth and is listed as ‘endangered’ on the International Union for Conservation of Nature Red List of Threatened Species.

Dr Sascha Usenko from Baylor University made the breakthrough by using the wax from a dead 12-year-old blue whale.

He found fluctuating levels of testosterone and the stress hormone, cortisol, during its life. At the time of its death, Usenko said the whale had twice as much cortisol in its blood than at any other point.

He believes this could relate to food availability, changes in social status, pollution exposure and environmental noise. Testosterone levels suggest the male blue whale reached sexual maturity at about 10 years of age.

‘The general increase in cortisol over the animal’s lifetime could be associated with a multitude of factors including weaning, development, sexual maturity, migration, food availability, environmental conditions, changes in social status, accumulated contaminant exposure or environmental noise,’ said Dr Usenko.

The study also showed the whale had accumulated substantial levels of pollutants – such as pesticides and flame retardants – within its first year of life during gestation or nursing.

In contrast mercury levels in the earplug – which measured around 10 inches – spiked during two distinct time periods later in the animal’s life.

The researchers suggest earplug analysis could help assessments of the impacts of human activities on marine organisms and their ecosystems.

‘Currently obtaining lifetime chemical profiles from birth to death is extremely rare and difficult for most of Earth’s animals,’ said Dr Usenko. 

‘We have developed a unique approach to quantify hormone and contaminant lifetime profiles for an individual blue whale using the wax earplug as a natural matrix capable of archiving and preserving these temporal profiles. 

‘Using a male blue whale earplug chemical analysis reveals lifetime patterns of mercury and organic pollutant exposure as well as fluctuating hormone levels.

‘We anticipate this technique will fundamentally transform our ability to assess human impact on these environmental sentinels and their ecosystems.

‘The use of a whale earplug to reconstruct lifetime chemical profiles will allow for a more comprehensive examination of stress, development, and contaminant exposure, as well as improve the assessment of contaminant use or emission, environmental noise, ship traffic and climate change on these important marine sentinels.’

Dr Usenko added the 70ft blue whale he studied was hit by a ship off the coast of California in 2007.

Blue whales are the largest mammal to have ever existed on Earth and grow up to 90ft and can weigh 150 tonnes.

They could once be spotted in all major oceans and numbers topped around 200,000, yet after being hunted almost to extinction, there is now thought be as few as 8,000.

The International Whaling Commission has taken steps to protect these creatures by appointing committees of experts to work against whaling, entrapment and predation, but their population remains low.

The findings were reported in the Proceedings of the National Academy of Sciences journal.

Source: Daily Mail