The Omura’s whale (Balaenoptera omurai) was described as a new species in 2003 and then later as an ancient lineage basal to a Bryde’s/sei whale clade. Currently known only from whaling and stranding specimens primarily from the western Pacific and eastern Indian Oceans, there exist no confirmed field observations or ecological/behavioral data. Here we present the first genetically confirmed documentation of living Omura’s whales, including descriptions of basic ecology and behavior from northwest Madagascar. Species identification was confirmed through molecular phylogenetic analyses of biopsies collected from 23 animals. All individuals shared a single haplotype in a 402bp sequence of mtDNA control region, suggesting low diversity and a potentially small population. Sightings of 44 groups indicated preference for shallow-water shelf habitat. Frequent observations were made of lunge feeding, likely on zooplankton. Observations of five mothers with young calves, and recordings of a song-like vocalization indicated reproductive behavior. Social organization consisted of loose aggregations of predominantly single individuals spatially and temporally clustered. Photographic recapture of a female re-sighted the following year with a young calf suggests site fidelity or a resident population. Our results demonstrate that the species is a tropical whale without segregation of feeding and breeding habitat, is likely non-migratory, and extends the range of this rare whale into the western Indian Ocean. Range restriction to tropical waters is rare among baleen whales, except for the various forms of Bryde’s and Omura’s whales. Thus, the discovery of a tractable population of Omura’s whales in the tropics presents the opportunity for understanding the ecological factors driving convergence of life history patterns with the distantly related Bryde’s whales.
Cerchio, S., B. Andrianantenaina, A. Lindsay, M. Rekdahl, N. Andrianarivelo, and T. Rasoloarijao. 2015. Omura’s whales (Balaenoptera omurai) off northwest Madagascar: ecology, behaviour and conservation needs. Royal Society Open Science 2:150301. The Royal Society. Published 14 October 2015.DOI: 10.1098/rsos.150301