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Omura’s whale much more widespread across the globe than previously thought

  • The global range of the world’s most recently discovered large whale species is starting to come into focus — as are the man-made threats to the species.
  • Salvatore Cerchio of the New England Aquarium in Boston, Massachusetts led a team that published a paper in Frontiers in Marine Science in March that includes a map of all known sightings of the elusive Omura’s whale (Balaenoptera omurai), demonstrating that the whale has a much larger range than previously thought.
  • Given the new information they had about the global range of Omura’s whale, the researchers determined the whales face threats from, “at minimum, ship strikes, fisheries bycatch and entanglement, local directed hunting, petroleum exploration (seismic surveys), and coastal industrial development.”

The global range of the world’s most recently discovered large whale species is starting to come into focus — as are the man-made threats to the species.

Salvatore Cerchio of the New England Aquarium in Boston, Massachusetts led a team that published a paper in Frontiers in Marine Science in March that includes a map of all known sightings of the elusive Omura’s whale (Balaenoptera omurai), demonstrating that the whale has a much larger range than previously thought.

A smaller member of the rorquals whale family, which also includes blue whales and humpbacks, Omura’s whale has now been spotted in tropical and warm temperate waters in every ocean basin on Earth except the central and eastern Pacific.

The filter-feeding baleen whales are known to frequent coastal waters, where they appear to feed primarily on krill and zooplankton. Like all other rorquals, they have long, deep grooves along their throats that allows their mouths to expand while feeding — and Cerchio and team’s paper also includes the first ever video of Omura’s whales during the feeding process.

When Japanese whalers caught Omura’s whales in the 1970s in the eastern Indian and western Pacific oceans, scientists initially mistook them for Bryde’s whales (Balaenoptera edeni brydei), though their smaller size led to the conclusion that they were some sort of pygmy Bryde’s whale. (Omura’s whales are typically between 33 and 38 feet long, whereas Bryde’s whales can reach as much as 45 feet in length.)

A team of researchers examined DNA evidence from eight whaling specimens and one stranded animal in 2003 and determined that the whales actually represented a species completely new to science. At that time, Omura’s whale was known to occur in just three locations: the southern Sea of Japan and in the vicinities of the Cocos (Keeling) Islands in the Indian Ocean and the Solomon Islands in the South Pacific.

It wasn’t until 12 years later that scientists were able to observe live Omura’s whales first-hand in the wild. Salvatore Cerchio led that team of researchers, as well. In a 2015 paper, Cerchio and colleagues described spotting Omura’s whales 44 times between 2011 and 2014. The researchers also captured and released the first video ever taken of the whales, which alerted marine biologists, ecotourists, and marine wildlife enthusiasts from around the world to be on the lookout for Omura’s whale. More than one hundred sightings of the species, once believed to be the mythical “ghost whale,” have now been reported.

In mapping those sightings of the species, Cerchio and team made use of all available sources, from published papers to unpublished reports and encounters described on the internet, all of which were substantiated by genetic, morphological, photographic, or acoustic documentation.

“Reports increased precipitously since 2015 after publication of the first detailed external description of the species, reflecting the impact of the recently elevated awareness of the species,” Cerchio and team write in the paper. They found 161 accounts of sightings from 95 locales in the waters of 21 range states. “The majority of accounts remain in the eastern Indo-Pacific suggesting a potentially recent range expansion from this region,” the authors add.

Their distribution in predominantly near-coastal waters puts Omura’s whales at risk from anthropogenic activities across its range, according to Cerchio and team, though the species’ “tropical distribution in often remote and poorly monitored areas makes adequately documenting and assessing threats challenging.” Given the new information they had about the global range of Omura’s whale, the researchers determined the whales face threats from, “at minimum, ship strikes, fisheries bycatch and entanglement, local directed hunting, petroleum exploration (seismic surveys), and coastal industrial development.”

Global map of Omura’s whale sightings around the world. Credit: Cerchio et al. (2019). doi:10.3389/fmars.2019.00067

The team also found evidence that some populations of Omura’s whale might be non-migratory and thus occur in restricted ranges. There also appears to be little genetic diversity throughout the species’ global distribution.

“Given the species may be characterized by small local populations, it may be particularly vulnerable to impacts from existing regional anthropogenic threats,” the authors write. “We recommend that focused work be conducted to locate and study local populations, assess potential population isolation, and determine conservation status and specific anthropogenic threats across the species’ range.”

Aerial photo of Omura’s shale mother and calf shot by a drone off the northwest coast of Madagascar in 2018. Photo Credit: S. Cerchio/Omuraswhale.org.
An Omura’s whale approaches the surface while feeding off the northwest coast of Madagascar. Photo Credit: Adapted from Cerchio et al. (2015), Royal Society Publishing.
Like all other rorquals, Omura’s whales have long, deep grooves along their throats that allows their mouths to expand while feeding. Photo Credit: S. Cerchio/Omuraswhale.org.
Aerial photo of Omura’s shale mother and calf. Photo Credit: S. Cerchio/Omuraswhale.org.

CITATION

• 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. doi:10.1098/rsos.150301

• Cerchio, S., Yamada, T. K., & Brownell, R. L. (2019). Global distribution of Omura’s whales (Balaenoptera omurai) and assessment of range-wide threats. Frontiers in Marine Science, 6, 67. doi:10.3389/fmars.2019.00067