What Whale Earwax Reveals About a Whale’s Life

A whale’s life is largely a mystery, but a unique biological structure provides a record of its existence. In some baleen and sperm whales, a substance called cerumen, more commonly known as earwax, builds up over time to form a solid earplug. This plug, which can grow to be nearly a foot long, creates a chronological archive of the animal’s life from birth to death, much like the rings of a tree.

The Formation of a Whale Earplug

The earplug is a dense accumulation of fats (lipids) and a fibrous protein called keratin. In many baleen whale species, the ear canal is sealed off from the ocean, allowing this waxy material to build up continuously throughout the animal’s life. This solid plug does not impede hearing; its density is similar to water, which allows sound vibrations to travel through the jaw and into the inner ear. The primary purpose of the earwax is to protect the delicate inner ear.

The wax is deposited in alternating light and dark layers, known as laminae. Each pair of layers, one light and one dark, represents one year of the whale’s life. The light-colored layers are richer in lipids and correspond to the feeding season when the whale consumes large quantities of prey. The darker, keratin-rich layers are associated with periods of fasting and migration when the whale relies on its fat stores.

Decoding a Whale’s Biological History

One of the most direct applications of the earplug is determining a whale’s age. By slicing the plug lengthwise and counting the light and dark layers, scientists can calculate how many years the whale lived. This method has been used since the 1950s and has been refined with modern analytical techniques. Age determination provides a framework for interpreting all other data extracted from the earwax, placing events into a specific life stage.

The earplug serves as a lifelong hormonal diary, capturing chemical markers of major life events. Scientists can analyze specific layers for different hormones to reconstruct a whale’s life events. For example, a spike in testosterone within a specific lamina indicates the onset of sexual maturity. In one male blue whale studied, testosterone levels increased 400-fold around the age of ten, pinpointing its transition to adulthood.

The wax chronicles periods of stress through the measurement of cortisol. An analysis of one whale revealed that its highest cortisol levels occurred shortly after reaching sexual maturity, suggesting stress related to competition for mates or other social pressures. For female whales, analysis of progesterone can reveal the number and timing of pregnancies.

Tracing Environmental Exposure and Migration

The fatty layers of the earplug also accumulate fat-soluble pollutants from the environment, creating a chronological log of exposure to human-made chemicals. As a whale swims, it absorbs contaminants that become trapped in its fatty tissues, including the earwax. Scientists can detect substances like the pesticide DDT, flame retardants, and mercury in specific layers of the plug.

Analysis of one whale born decades after the U.S. ban on DDT showed it was still exposed to the chemical throughout its life, demonstrating how persistent these pollutants are. The earplug shows that contaminant levels build over the whale’s lifetime, offering a more dynamic picture than a single tissue sample. This allows researchers to track when exposures occurred and assess how environmental contamination has changed over time.

Beyond pollutants, the earplug’s chemical composition can help reconstruct a whale’s movements. The analysis of stable isotopes, like carbon and nitrogen, provides clues about diet and geographic location. Because the chemical signatures of prey vary by ocean region, examining how these isotopic signatures change from layer to layer allows scientists to infer migrations between different feeding grounds.

The Science of Studying Earwax

The opportunity to study a whale earplug only arises after the animal has died. Scientists collect samples from whales that have washed ashore or died from other causes like ship strikes or entanglement in fishing gear. Since a global moratorium on most commercial whaling was enacted in 1986, these post-mortem collections are the primary source for new specimens. Museums also house historical collections of earplugs gathered during the whaling era for comparative studies.

Once in the laboratory, the earplug is prepared for analysis. It is sliced in half lengthwise to expose the layered structure. Researchers use precise tools, such as micro-drills, to extract a fine powder from each distinct lamina under a microscope.

The extracted powder is then subjected to advanced chemical analysis. Techniques like mass spectrometry are used to identify and quantify the specific molecules present in each layer. This allows for the detection of trace amounts of hormones like cortisol and testosterone, as well as various environmental contaminants.