In DepthMARINE MAMMALS

A whale's life, inscribed in baleen

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Science  11 Dec 2015:
Vol. 350, Issue 6266, pp. 1300-1301
DOI: 10.1126/science.350.6266.1300

In 2004, a collision with a ship cut short the life of an endangered North Atlantic right whale. Many lamented the death of Stumpy, as scientists called her—all the more because she was pregnant. But Stumpy's demise could ultimately help other whales. Researchers are using plates of her tough, hairlike baleen to develop a new method of reconstructing a whale's life story—much as scientists use growth rings to reveal a tree's past. The nascent technique could make it easier to study, and perhaps protect, whales.

Deriving whale biographies from baleen is just one concept to be discussed next week at the 21st Biennial Conference on the Biology of Marine Mammals in San Francisco, California. Some 3000 researchers will share insights into some of the world's most charismatic creatures, including first-time audio recordings of rare species and updates on struggling populations. They'll also discuss novel ways of assessing the health and physiology of free-swimming mammals that can be hard to study in the wild.

That's where the work involving Stumpy—and a second right whale named Staccato—will come in. Over the past decade or so, wildlife researchers have been figuring out how to pry life history information out of tissues based on keratin, the fibrous protein found in nails, hair, feathers, horns, claws, hooves, and skin. Researchers have used hair, for example, to study past drug use in humans and exposure to toxins in wildlife.

Keratin is also a major component of baleen, the comblike structures on the upper jaws of about 14 whale species that help the animals catch food. The tips of baleen plates—the comb's teeth—wear away over time, so whales continuously grow new keratin to replace what's lost. The new baleen stores chemicals, such as hormones or contaminants, which are circulating in the whale's blood at the time. That makes each plate—which can represent years or decades of growth—a time capsule, recording important life events such as pregnancies or exposure to stressful situations.

Hormones stored in the baleen of this bowhead whale, killed by native Alaskan hunters, can help tell its life story.

PHOTO: © GREGORY BULL/AP/CORBIS

Such information can be crucial to conserving rare species such as North Atlantic right whales, which number just about 500. When it comes to large whales, “there's no other animal on the planet where we know [so] little about basic reproduction,” says Kathleen Hunt, a research scientist at the New England Aquarium in Boston. For example, scientists don't know how long female right whales carry their calves, or how frequently they become fertile. They also can't easily tell whether the whales are experiencing harmful stress resulting from ocean noise, pollution, or other factors.

Hunt and Rosalind Rolland, a colleague at the aquarium, have already developed noninvasive ways to measure whale hormones associated with stress and reproduction. They involve going to sea to scoop up fresh dung or to collect “whale blow”—the air and droplets an animal exhales through its blowhole. But such samples provide only a snapshot of a whale's current physiological state. Hormone measurements from baleen promised a fuller backstory.

Baleen from Stumpy, a right whale killed by a ship, yielded a record of her pregnancies.

PHOTO: REGINA CAMPBELL-MALONE, WOODS HOLE OCEANOGRAPHIC INSTITUTION

Last year, the researchers published their first results from a pilot study of 16 bowhead whales killed as part of a legal hunt by native Alaskans. Bowheads are a long-lived species, and their baleen can record about 25 years of growth. In Conservation Physiology, a team led by Hunt and Rolland reported that not only could they detect two hormones in baleen—the stress hormone cortisol, and the reproductive hormone progesterone—they could also use them to distinguish males from females, and identify pregnant females. They also saw progesterone spikes that looked suspiciously like signatures of past pregnancies.

To know whether those signatures were real, the researchers needed baleen results they could match against documented whale pregnancies. Enter Stumpy and Staccato, also killed by a ship, in 1999. As a result of efforts by government agencies and conservation groups to monitor and protect right whales, scientists had records indicating when each whale had given birth to some of her calves.

In San Francisco, Hunt and her colleagues will unveil new results that suggest researchers can read baleen like a history book. When they analyzed plates from Stumpy and Staccato recording about 10 years of growth, they found that progesterone levels spiked in material dating to documented pregnancies, and then dropped for several years while the mothers were known to be raising calves and later traveling solo. The pattern was “incredibly striking and obvious,” Hunt says. That was a huge contrast to the “very subtle patterns” she's used to seeing in other kinds of whale data, she says. “Yeah! Most exciting results I'd ever seen in my career.”

The team has also been able to measure cortisol in the baleen, and they see patterns suggesting that stressors, such as getting entangled in commercial fishing gear, can interfere with a whale's ability to get pregnant. Stumpy's baleen, for instance, showed elevated cortisol levels after one pregnancy, and she didn't get pregnant again until the cortisol levels dropped.

Assuming the technique works in other baleen whales, researchers say it would be a welcome new tool. Currently, the only other way to reconstruct a whale's past is by analyzing the layers of wax that accrete in some whale ears. Both the wax and baleen can be collected only from dead animals, but Hunt notes that the wax doesn't last long and is rarely collected. In contrast, baleen is sturdy and long lasting. That could enable researchers to see far back in time by analyzing museum specimens of baleen, some of which are more than a century old, or whale remains found at archaeological sites.

Such “specimens are a treasure trove of biological information just waiting to be unlocked,” says ecotoxicologist Thea Bechshoft, a postdoctoral researcher at the University of Alberta, Edmonton, in Canada. The baleen work, she says, “adds to the growing evidence of how amazingly useful keratinous tissue … can be.”

  • * Rebecca Kessler is a journalist in Providence.

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