World-first video footage of one the rarest whales has emerged, leaving scientists stunned and proving yet again just how little we know of the ocean’s mysterious depths.

The Omura’s whale, discovered just over a decade ago and thought to be a close relative of the blue whale, has never actually been seen in the wild … until now.

For the first time ever, a team of marine biologists were able to observe and study the elusive creature in its natural habitat off the coast of Madagascar.

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“This is the first definitive evidence and detailed descriptions of Omura’s whales in the wild,” lead researcher Dr Salvatore Cerchio, from the New England Aquarium and Woods Hole Oceanographic Institution, said in a statement.

For decades, the 12-metre-long Omura’s whale was misidentified as the Bryde’s whale until 2003 when Japanese scientists used skeletal specimens and genetic tests to establish it as a distinct new species (named Balaenoptera omurai).

“What little we knew about these whales previously came from eight specimens of Omura’s whales taken in Japanese scientific whaling off the Solomon and Keeling Islands and a couple strandings of dead animals in Japan,” Dr Cerchio said.

And here lay the problem: although the species had finally been identified, there had still been no confirmed sightings.

Dr Cerchio’s team were conducting field research on dolphins in the tropical waters off the north-west coast of Madagascar when they first spotted the Omura’s whale in 2011, which was mistaken for a Bryde’s whale at the time.

In 2013, after they moved their study area further offshore, the sightings became much more frequent. During a few close encounters, they observed that, unlike the Bryde’s species, these whales had distinct asymmetrical black and white markings along the entire length of its body, with the right side being whiter and the left side darker.

“I was excited because I knew we had found Omura’s whale,’ Dr Cerchio told the BBC.

“Some teammates thought it might be a new species and began to think of new names.”

Professor Lars Bejder, a marine biologist and research leader at the Murdoch University Cetacean Research Unit, described the findings as “incredible”.

“It’s incredible to think that we’re in 2015 and we’re still finding a mammal on this planet of that size that we didn’t even know of,” Professor Bejder told The New Daily.

“They look like other species of whale that we thought we knew, and if we only get small glimpses of it, then by default think it’s a species that you already know.”

Over a two-year period, Dr Cerchio’s team observed 44 groups and collected skin biopsies from 18 adult Omura’s whales and catalogued approximately 25 individual whales through photographic identification.

They found it exhibited lunge-feeding behaviour by taking in large mouthfuls of water and filtering it through the hairy sieve-like teeth, known as baleen, and that they most likely fed on tiny zooplankton.

The researchers also observed that it might be non-migratory due to a lack of segregation of its feeding and breeding habitats.

But Professor Bejder cautioned that it was still too early to draw conclusions about migratory behaviour without further research.

“Usually, larger baleen whales do migrate. Look at humpback whales, they carry out the world’s longest migrations where they feed in the Antarctic and colder waters and come up to the tropics to breed in winter times.”

Dr Cerchio will return to Madagascar in November to further study the whales’ vocalisations, behaviour and population characteristics, and is looking at tagging the animals to track them in other parts of its range.