Fundy Tides: WHO WOULD HAVE THOUGHT! The History of the Oceans Is Locked in Whale Earwax

The Astonishing History Locked in Whale Earwax - The Atlantic:

ED YONG, NOV 21, 2018

A humpback whale jumps out of the ocean — MIGUEL MEDINA / GETTY

Whales are big, whales are long-lived, and whales have paddle-shaped flippers instead of dexterous hands. These three traits inexorably lead to a fourth: Over time, whales accumulate a lot of earwax.

Whale earwax forms like yours does: A gland secretes oily gunk into the ear canal, which hardens and accumulates into a solid, tapering plug. In the largest whales, like blues, a plug can grow up to 10 inches long, and looks like a cross between a goat’s horn and the world’s nastiest candle. Fin whale wax is firmer than blue whale wax, bowhead whale wax is softer and almost liquid, and sei whale wax is dark and brittle. But regardless of size or texture, these plugs are all surprisingly informative.

plugs. Much as with tree rings, you can count the bands to estimate a whale’s age. And you can also analyze them to measure the substances that were coursing through the whale’s body when each band was formed. A whale’s earwax, then, is a chronological chemical biography.

As whales go through their annual cycles of summer binge-eating and winter migrations, the wax in their ears changes from light to dark. These changes manifest as alternating bands, which you can see if you slice through the plugs. Much as with tree rings, you can count the bands to estimate a whale’s age. And you can also analyze them to measure the substances that were coursing through the whale’s body when each band was formed. A whale’s earwax, then, is a chronological chemical biography.

Stephen Trumble and Sascha Usenko from Baylor University have worked out how to read those biographies. And they’ve shown that whale earwax not only reveals the lives of their owners, but the history of the oceans. Hunting, abnormal temperatures, pollutants—it’s all there. If all of humanity’s archives were to disappear, Trumble and Usenko could still reconstruct a pretty decent record of whaling intensity by measuring the stress hormones in the earwax of a few dozen whales.

The duo first tested their idea of studying earwax by analyzing the plug from a single blue whale—a 12-year-old male that was fatally struck by a ship off the coast of Santa Barbara in 2007. They could tell that the whale became sexually mature when it was 9 years old, as that’s when testosterone levels in the plug shot up by 200 times. They showed that the stress hormone cortisol peaked a year before that, perhaps a sign of the creature’s changing body and mind. They found traces of pesticides and flame retardants that were especially concentrated in the whale’s first six months of life, and had likely been passed down in its mother’s milk. “I was surprised at how well [the technique] worked, not only for persistent chemicals but for hormones that typically rapidly degrade,” Usenko told me at the time.

That was just one earwax plug, but it was surprisingly easy to get more. They just had to call curators at the right natural-history museums. “Museums are notorious for collecting everything, and waiting for the science to catch up,” Trumble says. “We called Charles Potter at the Smithsonian Institution, and he said, ‘It’s interesting you called because we have pallets and pallets of these ear plugs sitting around, and we’re thinking of throwing them away.’ Instead of being thrown away, those ear plugs are now objects of wonder.”

Trumble, Usenko, and their colleagues ended up measuring cortisol levels in the plugs from 20 blue, fin, and humpback whales, the oldest of which had been born in 1871. The team measured how this stress hormone varied over the lifetime of each animal, relative to the lowest levels found in each plug. They then combined these readings into a 146-year chronicle of whale stress, which they compared to a record of all whaling data from the 20th century. “We plotted the two together, and were like: ‘You’ve got to be kidding me,’” says Trumble.

A graph comparing whaling intensity with earwax cortisol. (Trumble et al, 2018, *Nature* communications)

The two data sets matched beautifully. When whaling increased, cortisol levels rose, hitting their peak during the heyday of whaling in the early 1960s. After moratoriums were adopted in the 1970s, whaling harvests fell by 7.5 percent a year and cortisol levels in earwax fell by 6.4 percent a year.