In the shallow waters of coastal Madagascar, a team of biologists from the Woods Hole Oceanographic Institution have made the first field observations of one of the least understood whale species – Omura’s whales. Salvatore Cerchio, lead author of the study, says ‘this is the first definitive evidence and detailed descriptions of Omura’s whales in the wild and [it is] part of what makes this work particularly exciting.’
Until 2003, Omura’s were thought to be a pygmy type of the Bryde’s whale owing to their similar dorsal fins and tropical range. However, genetic data from stranded carcasses classed them as their own species. They are understood to be smaller than Bryde’s whales and to have unique markings: a dark jaw on the right and a lighter jaw on the left. ‘They appear to occur in remote regions and are difficult to find at sea because they are small,’ says Cerchio. ‘They range in length from approximately 33 to 38 feet – and do not put up a prominent blow.’
Initially, Cerchio and his team were surprised to see the Omura’s whale. The first, spotted in the Nosy Be region in 2011, was originally misidentified as a Bryde’s whale too, mainly because, according to Cerchio ‘from the little information there was on their habitat and range, Omura’s whales were not supposed to be in that part of the Indian Ocean.’
The sightings increased when they moved to a different site in 2013, where the team has now catalogued approximately 25 individuals through photo identification. They have observed the Omura’s lunge feeding, possibly for zooplankton, as well as the behaviour of four mothers with young offspring. ‘The presence of mothers with young calves suggests that our study site probably represents breeding habitat where females give birth,’ say the authors.
Recordings of their vocalisations were also made, which the study says are often choruses between multiple individuals. For now, the team predict that the Omura’s whale song is a male-limited trait, however, Cerchio will carry out further study on the behaviours and vocalisations in the field. He hopes to produce the first estimate of abundance for any population of the rare species.
With the first detailed description of their appearance and behaviours, the team hopes that it will be easier to distinguish Omura’s from Bryde’s whales in the future.