- A handful of unusual whale specimens were recognized as a separate species called Omura’s whale (Balaenoptera omurai) in 2003.
- Until now there have only been a few unconfirmed sightings of living Omura’s whales.
- A new study describes 44 observations of the whales off northwestern Madagascar, providing the first confirmed description of living Omura’s whales, including photos, videos, and audio recordings.
In the waters off Madagascar, scientists have at last encountered living members of a species of whale known only from old, dead specimens. Shaped like a sleek torpedo, with unusual asymmetrical markings, the elusive Omura’s whale has for the first time been documented in photos, videos, and audio recordings.
In the 1970s, scientists initially classified eimadaght whales killed by Japanese whalers in the eastern Indian and western Pacific oceans as Bryde’s whales (Balaenoptera edeni). Measuring between 33 and 38 feet long, the animals were considered smaller “pygmy” Bryde’s whales, which usually measure around 45 feet long.
It wasn’t until 2003 that another team of researchers, examining DNA evidence from the eight whaling specimens and a stranded animal, concluded that the whales actually belonged to a new-to-science species that came to be called Omura’s whale (B. omurai). Subsequent studies have identified other stranded or hunted animals as members of the same species based on DNA and skeletal evidence.
Up to now, however, there have been no first-hand observations of living Omura’s whales described in the scientific literature that could shed light on the animals’ behavior, biology, or ecology; only a handful of unconfirmed sightings.
In 2007 a team led by Salvatore Cerchio, a marine mammal biologist then with the Wildlife Conservation Society, began studying cetaceans off the northwestern coast of Madagascar. Starting in 2011, they began spotting a few small rorqual whales — species with deep grooves on their throats that enable expansion during feeding.
“At first, we thought they were Bryde’s whales, an understandable mistake because of the similar size and habitat,” Cerchio said in a press release.
In 2013 and 2014 the team shifted to a different study site and were able to make extensive observations of the whales, including underwater photos and videos.
“When we clearly saw that the right jaw was white, and the left jaw was black, we knew that we were on to something very special,” said Cerchio, who currently holds positions with the New England Aquarium and Woods Hole Oceanographic Institution in Massachusetts.
“The only problem was that Omura’s whales were not supposed to be in this part of the Indian Ocean. Rather, they should be in the west Pacific, near Thailand and the Philippines,” he added.
To confirm their hunch, Cerchio’s team gathered skin biopsies from the whales and had the DNA tested by a lab at Northern Michigan University. Sure enough, it was a match with the Omura’s whale. They published their findings last month in the journal Royal Society Open Science.
In the paper, the researchers describe spotting Omura’s whales 44 times between 2011 and 2014. The whales always appeared singly or in pairs, although these usually showed up in what they call “loose aggregations” of up to six animals spaced a few hundred meters apart.
They observed the whales feeding, apparently on zooplankton, as well as breaching and defecating. They recorded Omura’s whale vocalizations and gathered photographic evidence identifying about 25 individuals. They also spotted four mother whales with calves young enough to hint that the area might be a calving ground. Other evidence suggests the whales may reside there year-round.
All of those are firsts for the species. The team plans to continue its observations in northwestern Madagascar this month.
With such a scanty record of sightings and so very little known about the mysterious species, the conservation status of Omura’s whales remains unclear. But the researchers note in their paper that the animals’ shallow-water habitat makes them likely to become accidentally entangled in fishing gear. They also write that the Omura whales’ low-frequency communications make them vulnerable to noise pollution, and that loud hydrocarbon exploration and production is ongoing in the whales’ Malagasy home waters, with more planned for the future.
Citations
- 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: 150301.
