Whales are among the largest animals to have ever lived on Earth, so how could a whale species go undetected until recently, much less have never been seen alive in photos or video. Dr. Salvatore Cerchio of the New England Aquarium and Woods Hole Oceanographic Institution (WHOI) and an international team of whale biologists have just released images and detailed descriptions on the first scientific observations in the wild ever of Omura’s whales, one of the least known species of whales in the world. So little is known about the Omura’s that scientists are unsure of how many exist or how rare the species is.
|Adapted from Cerchio et 2015|
In a recently published paper in the prestigious Royal Society Open Science journal, the researchers describe the Omura’s foraging techniques, vocalizations and habitat preferences in the shallow coastal waters of Madagascar. This description of the live behavior of Omura’s whales is a first as there had been no confirmed records of sightings in the wild, and little else had been known about this elusive species until now.
Omura’s whales (Balaenoptera omurai) are a relatively small baleen whale ranging in length from 33 to 38 feet. They are from the from whale family called rorquals, which all have long, deep grooves along their throats that can expand when they feed. Omura’s whales are the smaller cousin in this group that includes the giant blue whales and the acrobatic humpbacks.
This species was only first identified as a distinct species in 2003 from the DNA of dead specimens from old Japanese whaling expeditions and strandings in the tropical western Pacific and Indian Oceans. These rare whales had long been misidentified as a dwarf version of Bryde’s whales, which are another rorqual whale averaging in the mid-40 foot range for length.
"Over the years, there have been a small handful of possible sightings of Omura's whales, but nothing that was confirmed," says lead author Cerchio, who led the research while at the Wildlife Conservation Society. “They appear to occur in remote regions and are difficult to find at sea, because they are small and do not put up a prominent blow."
Cerchio and his colleagues had been conducting field research on marine mammals off the northwest coast of Madagascar since 2007. In 2013, they began to make frequent observations of unusually-marked whales that piqued their curiosity. Cerchio said, “At first, we thought they were Bryde’s whales, an understandable mistake because of the similar size and habitat, but then with good photographs and underwater video, we noticed they more closely resembled the description of Omura’s whales.”
The key clue to the mysterious whales was an uneven coloring on the head, a rare characteristic found in only one other whale species – fin whales, which are much larger. “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. “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.”
Cerchio and his Malagasy team excitedly suspected that they were observing and documenting the first sighting of Omura’s whales in the wild. To irrefutably confirm their hypothesis, they needed to collect skin biopsies and confirm the DNA signature of the species. They submitted samples to the lab of Dr. Alec Lindsay at Northern Michigan University (NMU). Sequencing mitochondrial DNA, the NMU team confirmed the field observations. “The DNA evidence was conclusive,” added Lindsay. “The 23 samples collected by Sal’s field team were from Omura’s whales. His field team’s detailed behavioral and ecological observations constitute the very first descriptions of these whales in the wild.”
The research team also observed four mothers with young calves. Using hydrophones, they recorded song-like vocalizations that may indicate reproductive behavior.
Cerchio will return to the field in November to do further study on the whales' vocalizations, behavior and population characteristics. He also hopes to expand the research area in future studies of Omura's whales, working with colleagues at WHOI to deploy Digital Acoustic Recording Tags (DTAGS) and to study the species in other parts of its range.
Cerchio hopes to produce the first estimate of abundance for any population of Omura’s whales with the work off Madagascar. So far, the team has catalogued approximately 25 individuals through photographic identifications.
Additional coauthors of the paper include Melinda Rekdahl of the Wildlife Conservation Society, and Boris Andrianantenaina, Norbert Andrianarivelo, and Tahina Rasoloarijao of the Institut Halieutique et des Sciences Marines, Universite de Toliara, Madagascar.
The work was supported by the International Whaling Commission Small Cetacean Conservation Fund, the U.S. Marine Mammal Commission and the Prince Albert II Conservation Fund.