Two clans of whales use different dialects to communicate.
For over a decade, Canadian marine biologist Shane Gero has been spending months at a time following sperm whale families near the Caribbean island of Dominica, which seems to be some kind of haven for these deep-ocean giants. They're among our planet's least-understood creatures, because they're so inaccessible—sperm whales can dive up to 2,000m down to hunt for prey like giant squid, and can hold their breath for up to 90 minutes—but Gero has come to see them as humanlike, at least in some ways.
In his time running the Dominica Sperm Whale Project, Gero, who's affiliated with Aarhus University in Denmark, has come to believe that these whales have a distinct set of vocalizations, or dialects, that define their cultural groups—and that they may even have what he terms a "civilization." Any conservation measures aimed at protecting endangered whales, he told me, have to take their cultural groups into account.
Civilization is a sticky term, one we associate with humans. What Gero means here is a set of traditions passed down through generations of whales, and that's harder to argue with. These animals communicate through a series of clicks called "codas" (distinguishable from the echolocation clicks they emit to hunt in the deep ocean), which differ among whales found in different parts of the ocean, and in different families or clans. Shortly after they're born, sperm whale babies begin to "babble," Gero said, and pick up a language.
Because male sperm whales leave for the poles once they're grown, babies are raised by their mothers and other female family members. But sperm whale calves aren't physiologically able to dive deep with their mothers for their first few years of life, so close family members watch the calves when mom goes hunting for squid, Gero said. Babies pick up codas from their mothers and babysitters in this way.
(Sperm whales aren't the only marine mammals to have distinct dialects. Killer whales, for one, also emit communication signals that differ between families, or pods.)
In a study out Wednesday in Royal Society Open Science, Gero and co-authors outline a previously unknown sperm whale "vocal culture" in the Caribbean. In other words, they've now pinpointed two distinct dialects among families of whales that live in the same waters. Whales with different dialects avoid each other, suggesting some sort of "cultural identity at the clan level," which is also seen in Pacific whales.
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"This came out of nowhere," Gero told me. Although Pacific whales are known to move in "multicultural" circles, and different dialects are spoken by families in the same areas, Caribbean whales were believed to be much more homogeneous, emitting a standard 1+1+3 coda (two staccato clicks, followed by three more rapid ones).
"We came at this by saying, why do we see multicultural areas in the Pacific?," he said.
The just-identified clan of Caribbean whales "almost never makes the 1+1+3," Gero explained, and instead makes a long, slow coda of five evenly repeated clicks.
Sperm whale clans don't just have different dialects—they seem to behave differently, too, Gero said, which suggests these dialects are cultural markers of some kind. For example, these animals might forage somewhat differently, or travel different routes. Culture could help explain why the sperm whales around Dominica like to stay close to the island, and don't roam around as much as other whales. Some animals in the Pacific, on the other hand, will range over thousands of kilometers.
Culture is also a "boundary" for social interaction, as Gero puts it. Whales from different vocal clans spend no time together. So he thinks it must mean something significant to the animals as well.
Dominica's whales are facing all sorts of pressures. Calf mortality is as high as 29 percent in the first year of life, Gero told me. Agricultural contaminants, fishing practices, tourism, and a lot more all seem to be impacting them.
To this marine biologist, the discovery of a new vocal culture make preserving endangered sperm whales even more critical—and suggests to him that it isn't just a numbers game. He hopes that, at some point, whales' "cultural stocks" will be managed, and not just their geographical ones.
"Managing the conservation of cultural animals means understanding cultural boundaries, not just keeping the numbers up," he said. "If all the anthropogenic impact is on just one cultural group of whales, what happens when you lose that group?"
With it, a culture disappears.