A whale whisker has told scientists the life story of one of the rarest of whales

Scientists studied the whisker plates of seven dead Rice whales and found hormonal traces of stress, pregnancy and possible breeding patterns. The work was published in PLOS One. According to the authors, there are fewer than 50 adults of the species left, making the Rice whale the most threatened species among killer whales.

Important: The study does not reveal the entire life of the species in its entirety. The sample is very small because it's nearly impossible to get such samples from rare whales. But even seven animals gave scientists rare data about what happened to them in the months and years before they died.

Details

Whale whiskers aren't teeth. They're long plates of keratin, a similar material to what makes up hair and fingernails. They hang from the upper jaw and act as a filter: the whale draws water from its prey and then filters it through the whisker plates.

It turns out that these plates can also be a kind of diary. They grow gradually, and in them are deposited hormones that circulated in the animal's body. Therefore, different parts of the plate can be used to reconstruct not just one moment, but a sequence of events.

In the new study, scientists measured four hormones: progesterone, testosterone, cortisol and corticosterone. Progesterone helps see signs of pregnancy, testosterone is linked to male reproductive activity, and cortisol and corticosterone are related to stress hormones. Samples were taken every centimetre of the whisker plate; such a section roughly corresponds to 15-30 days of growth.

A particularly prominent signal was found in two whales that had probably suffered long periods of emaciation before death. In the newest layers of their whale whiskers, levels of all four hormones rose sharply. Similar patterns have already been described in other whales with prolonged illness, trauma or severe condition before death.

In one adult female, the researchers saw prolonged elevated levels of progesterone. Such a signal is consistent with a recent pregnancy. This is important because Rice whales have almost no breeding records: the animals are too few and far from shore, and it is difficult to see a pregnancy or calf being born.

In the three adult males, scientists found no pronounced annual peaks in testosterone. In many whales, such peaks are associated with the breeding season. Rice's whales did not show such a pattern in these samples, so the authors cautiously suggest that the species may not have a strictly defined mating season. But this is a tentative conclusion - new data are needed to be sure.

Why it matters

Rice's whales are difficult to study using conventional methods. They live year-round in the Gulf of Mexico, and their numbers are extremely small. NOAA estimates the total number of the species at less than 100 individuals; the latest estimate for the northeastern Gulf is about 50 animals.

For a species like this, any information about pregnancy, stress, causes of mortality, and breeding seasons is important not only for science, but also for conservation. If researchers understand when animals breed, how they respond to prolonged exhaustion or injury, and which threats affect them most, protective measures can be made more precisely.

In doing so, whale whiskers provide a rare opportunity to study an animal's condition after its death. This is especially important because taking regular samples from living Rice's whales is nearly impossible.

Background

Rice's whales were long considered a population of Bryde's whales, but in 2021 they were recognised as a separate species based on genetic and morphological data. They are now known as a resident species in the Gulf of Mexico.

The main threats to them come from human activities: collisions with ships, noise, oil and gas infrastructure, oil spills, debris, climate change, and entanglement in fishing gear. NOAA also notes that the species has been hit hard by the Deepwater Horizon accident, with oil affecting an estimated 48% of Rice's whale habitat in the eastern Gulf, and numbers could have dropped as low as 22%.

So the new study is important not only as an unusual scientific method. It adds data about the physiology of a species that could disappear before people have time to study it well.

Source

Rebecca G. Evey et al, "Baleen hormone analyses reveal stress and reproductive life-history of the critically endangered Rice's whale (Balaenoptera ricei)", PLOS One, 2026. The article was published on 13 May 2026.

In the study, the authors examined the whale whiskers of seven dead Rice's whales: four males and three females. They measured progesterone, testosterone, cortisol and corticosterone to reconstruct signs of pregnancy, reproductive activity and physiological stress. The work has shown that whale whisker analysis can be a useful tool for studying rare whales, but conclusions are still limited by the small number of samples available.