You can tell a lot from a person’s fingernails (don’t look at mine!). Fingernails are made of a tough protein called keratin (from the Greek keras, meaning horn). If you are suffering from anemia, your fingernails may be white at their bases. If your nails are yellow, you could have a problem with your respiratory system. Other changes to the color or shape of fingernails may indicate diabetes, auto-immune ailments or other systemic illnesses.

But human beings aren’t the only creatures to produce keratin. We make fingernails; whales make baleen. So what can baleen tell researchers about the health and well-being of whales? 

Humpback, bowhead and right whales grow baleen plates in their mouth. They use the enormous plates to filter seawater for food. That food typically is microscopic phytoplankton and zooplankton, which the whales eat by the ton. A humpback whale might have 600 flexible baleen plates in its upper jaw, which can grow 15 centimeters or more each year. Each plate is rimmed with a ring of stiff hair-like fringe; the fringe of the plates overlap, forming a living mesh. To feed, a humpback whale swallows huge amounts of seawater, then pushes the water out through the baleen plates with its giant tongue, trapping food behind. A right whale, by contrast, moves slowly through the ocean with its mouth open; seawater flows into the front of the mouth and out in between the baleen plates.

Most whales are strictly protected by national and international law; gaining access to any component of their bodies to determine their health, such as blood, is extremely difficult. So Kathleen Hunt, a research scientist at the New England Aquarium in Boston, decided to use various proxies, such as feces, whale breath and now baleen, to study whale physiology.

Whales are air-breathing mammals. They must surface to breathe and when they do, they exhale their held breath forcefully out a blow hole. Hunt suspected that all the constituents found in a whale’s blood, such as hormones, also would be found in its exhaled breath. Capturing breath from a whale required a bit of ingenuity: she made her own breath sampler out of a plastic bottle wrapped with a nylon veil attached to a long pole. Then came the tricky part: maneuvering near enough but not too near a multi-ton whale when it surfaced in order to sweep the contraption through the exhaled breath. 

It sounds like a recipe for disaster but, surprisingly, the procedure worked. In 2009 Hunt and her colleagues published a scientific paper showing that they could detect the sex hormones progesterone and testosterone as well as the stress hormone cortisol in the breath of humpback and North Atlantic right whales. The presence and amount of progesterone and testosterone indicate the animals’ sex and reproductive state. 

Now Hunt is examining whale baleen to gather similar data. Because baleen, just like human fingernails, is constantly renewed during a whale’s life, it provides a long-term record of the animal’s health. But getting access to baleen proved difficult because of the legal prohibitions against harming whales. Eventually Hunt collaborated with native Alaskans in Barrow, who annually hunt bowhead whales for food. She was able to examine baleen taken from 16 bowheads killed during the hunt. By analyzing the keratin, Hunt found detectable levels of cortisol and progesterone in the baleen plates. She also found spikes in progesterone levels that might indicate past pregnancies. Her work had added significance because bowhead whales are closely related to endangered North Atlantic right whales.

To corroborate the findings, Hunt and her team then examined baleen taken from two right whales accidentally killed in 1999 and 2004. The whales had been tracked over the years, so scientists knew the times at which each had been pregnant and given birth. Hunt found that the levels of progesterone in their baleen corresponded to times of known pregnancy, then dropped off after each birth. The fact that baleen can provide these sorts of data has importance to whale researchers. The duration of time between pregnancies gives clues about the health status of the mother whale. If that period is longer than usual, something isn’t right with the female. If cortisol levels are high, that suggests that the animal is under either man-made or natural stress. 

This research is important in our part of the world because North Atlantic right whales aren’t doing very well. Although the population began to grow at an encouraging rate in the early and mid-2000s, it has recently slowed significantly. Fourteen right whale calves were born this year; 17 were born in 2015 in a population of approximately 500. The birth rate has declined by 40% since 2010, an ominous slide for a species precariously close to extinction. Scientists don’t know if the whales are miscarrying or not getting pregnant at all. Studying whale “fingernails” may give them some clues.