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Biology

Whale earwax: a hearing aid & time capsule

Created by Megan Chen, based off an idea by Justine Bassett

Created by Megan Chen, based off an idea by Justine Bassett

 

Let’s Dive Right In

Whale earwax: a topic that has probably never crossed your mind. The existence of whale earwax should not be overwhelmingly surprising, considering that like us, they are mammals. However, because whale ear openings are tiny compared to the rest of their body (e.g. blue whale ear holes range from the size of a pencil point to eraser tip in diameter!), it may be that whale ears are not obvious enough to prompt deep thoughts about whale earwax.

All cetaceans (whales, dolphins and porpoises) produce earwax. In some species of baleen whales and in sperm whales, whale earwax can build up in layers over time to form an “earplug” that sits in the ear canal.

Humpback whales hanging out with their earwax (Credit: Ed Lyman, NOAA National Marine Sanctuaries)

Image 1: Humpback whales hanging out with their earwax (Credit: Ed Lyman, NOAA National Marine Sanctuaries)

Whale earplugs are extremely valuable to whale survival for two main reasons:

  1. They are a built-in hearing aid:

Whales rely more on their sense of hearing than sight. They use sound for navigation, foraging for food and for communication, useful for finding mates. Whales can communicate and hear over thousands of miles! However, whales do not hear like land mammals do because water is five times more dense than air. If whale ears were filled with air like our ears, there would be a mismatch between how sound travels in water and how it travels through whale ears—this is called acoustic impedance mismatch. The density of the earwax that sits in the ear canal (external ear) is a similar density to water, thereby allowing sound to travel through the ear canal into the inner ear unimpeded.

 

  1. They are a time capsule holding years in ears:

If you slice a whale earplug lengthwise, it will reveal alternating light and dark layers. Light layers are associated with periods of feeding because there are more lipid droplets from prey interspersed between wax cells. Dark layers are associated with migration or when the whale is not feeding. Counting the layers represents an accurate proxy for age, although different species of whales excrete earwax at different rates.  In blue whales, one light layer and one dark layer represents one year of life.

earplug

Image 2: Unidentified earplug from the Smithsonian’s National Museum of Natural History collections. Note the light and dark layers. (Credit: Megan Chen)

This technique is not new. Scientists have been using earplugs to age whales since the 1950s. In fact, many earplugs were collected between the 1950s-1960s at “whaling stations” when commercial whaling for meat, oil, blubber and baleen was common. A few museums, including the Smithsonian’s National Museum of Natural History (NMNH), hold collections of earplugs from this time. To some, these collections may seem redundant and scientifically useless after all the layers have been counted. However, science is not done with whale earplugs just yet!

Recent advances in technology have allowed scientists to chemically analyze traces of compounds in each waxy layer of an earplug, opening a whole new dimension of research possibilities within an earplug collection. Fun fact: removing each layer is painstakingly hard requiring a microscope, a steady hand, many hours and many cups of coffee.

 

An Example: Decoding the Life History of a Blue Whale

Using modern techniques, Dr. Stephen Trumble and co-researchers were able to quantify lifetime levels of two hormones and forty-two contaminants from a single 10-inch earplug obtained from a male blue whale that died in a ship strike.  It is worth mentioning here that in 1986, a moratorium on commercial whaling came into effect, so nowadays (with very few exceptions), earplugs can only be collected from whales that have died from ship strikes, entanglement in fishing gear or strandings.

Graph

Image 3: Graph depicting hormone levels throughout a male blue whale’s life. (Data from Stephen J. Trumble, PhD)

For this male blue whale, results showed that he reached sexual maturity around 10 years old, and felt the most stress shortly after—finding a mate is never easy (see Image 3).  Exposure to pesticides and flame retardants that have been banned for several decades were highest when the whale was 0-6 months old, showing maternal transfer, and chemical persistence. Mercury did not follow the same trend.  Instead, it had lower maternal transfer, but two later peaks that could be the result of feeding in highly contaminated industrial areas. To date, this is the only earplug fully analyzed in this way, although there are certainly more in the works.

 

So what?

Studying earplugs gives us a chronology (± 6 months) of life history information that was previously unavailable.  This is significant because whales are part of a healthy ecosystem, they have cultural significance and they are at the centre of a $2.1 billion ecotourism industry! Unfortunately, many whales–including blue whales–are endangered due to historical hunting, and are currently facing challenges to recovery such as noise pollution (it makes communication difficult), entanglement in fishing gear, etc. By examining stress levels and levels of contaminants of current whales, then comparing them to historical baselines using museum collections, we can assess what impacts humans have had and currently have on whales and marine ecosystems. This type of information can then be used to develop management plans to reduce threats, facilitating recovery.

To recap: whales can’t live without their earwax, and perhaps, given their ecological and economic significance, neither can humans.

Image 4: Scientists and tourists on board a whale watching vessel in Skjálfandi Bay, Iceland, admire a surfacing humpback whale. (Credit: Megan Chen)

Image 4: Scientists and tourists on board a whale watching vessel in Skjálfandi Bay, Iceland, admire a surfacing humpback whale. (Credit: Megan Chen)

 

Shameless promo: I’m developing a self-guided activity for the Smithsonian’s National Museum of Natural History on whale earwax that should be on the floor next month!  If you are in the area, please feel free to come check it out! Also many thanks to Dr. Steve Trumble, Dr. Sascha Usenko of Baylor University and of course, Charley Potter (NMNH) for sharing their research and time, answering countless questions, and generally being awesome!

Discussion

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