Planet Earth

Mysterious Whales Seen Alive for the First Time

InkfishBy Elizabeth PrestonOct 28, 2015 7:03 AM


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Never heard of an Omura's whale? There's a good reason. Until recently, no one had laid eyes on one in the wild. Before 2003, the Omura's whale was thought to be simply a dwarf version of another type of whale. Then Japanese scientists studying the whale's DNA and bodily characteristics decided it ought to be its own species, and named it after the late cetologist Hideo Omura. Still, all they had to work with were carcasses caught by whalers or washed up on the beach. They gleaned what information they could from the animals' ear wax and stomach contents, but no one had ever seen Balaenoptera omurai swimming or eating or interacting. Pretty much all scientists knew was that it lived in the western Pacific. Imagine the surprise, then, of researchers in a boat in the Indian Ocean when they spied some Omura's whales in the distance. During a survey of marine mammals off Madagascar's coast, New England Aquarium scientist Salvatore Cerchio and his colleagues saw whales with markings that seemed to match B. omurai. They used biopsy darts to snag tissue samples from 18 of the whales as they swam by. DNA analysis confirmed it: the animals were the elusive Omura's whales. Over the next few years, the scientists returned and recorded every detail they could about this population. Since they were the first humans to observe Omura's whales in nature, everything they learned about the animals was new:They're lopsided After 44 sightings, along with underwater video of three individuals, the scientists had a much better idea of what Omura's whales look like. Adults are 8 to 12 meters long, and calves are half that size. (The researchers estimated these numbers by waiting until the whales swam close by, then comparing their length to the boat itself, which was about one whale long.) The animals are mostly dark gray but have a big white patch on their right lower jaw, as if wearing a lobster bib that got pushed over to one side.

Letter A shows the Omura whale's asymmetrical white jaw patch. They're enthusiastic eaters Like the other rorquals—the group that B. omurai belongs to—Omura's whale likes to "lunge feed." This means just what it sounds like. A whale gapes its mouth wide open, then plows through a patch of food. Rorquals have grooves on the undersides of their throats that act like pleats, allowing the mouth to stretch. The researchers didn't see any fish during these lunge feedings, so they think the whales may have been eating zooplankton (assorted ultra-small animals that drift in the ocean). They don't get out much The scientists also didn't see any evidence that Omura's whales make migrations. Based on the calves they glimpsed, they think at least some females are using this area to mate and have babies. And based on the DNA samples, they know the whales here have low genetic diversity—they're all pretty similar to each other. So the Madagascar Omura's whales may be a small, local population that stays put. On the other hand, there are Omura's whales in an entirely different part of the world from where they'd been found before. So while individual whales may not travel much, the species as a whole is much more widespread than it had seemed. They're loners The scientists most often saw whales swimming alone. A handful of times, they saw a mother with her calf. Only twice did they see adult whales swimming together, and those hangouts lasted ten minutes or less. But they sing together A microphone hanging from the boat captured recordings of Omura's whales singing. Their calls were distinctive, with a consistent rhythmic pattern. Although the whales didn't swim close together, they often traveled in loose aggregations—say, a half-dozen animals within a few hundred meters of each other. This was close enough for their songs to overlap. The microphone sometimes captured choruses of multiple whales singing at the same time. The researchers think vocal communication may be a major part of the whales' lives, as it is in related species like the humpback. The song of the Omura's whale might be a display that males use to show off. Either that, or the whales are saying, "What are these weird floating animals we've never seen before?" Images: Cerchio et al.

Cerchio, S., Andrianantenaina, B., Lindsay, A., Rekdahl, M., Andrianarivelo, N., & Rasoloarijao, T. (2015). Omura’s whales (Balaenoptera omurai) off northwest Madagascar: ecology, behaviour and conservation needs Royal Society Open Science, 2 (10) DOI: 10.1098/rsos.150301

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