A Recent Stranding of Omura’s Whale (Balaenoptera omurai) in Western Australia

Abstract

Omura's whale ( Balaenoptera omurai ), described in 2003, is a putatively rare rorqual species known mostly from waters in the lower latitudes of the Indo-Pacific. A small (5.68 m) baleen whale that stranded near Exmouth on the northwestern coast of Australia in March 2015 was initially thought to be a small Omura's whale (although unknown for the area) or a Bryde's whale ( B. brydei ). Morphological assessment showed the whale had a strongly falcate, steeply angled dorsal fin characteristic of Omura's whale and a slightly prominent single median ridge but was smaller in size than was typical for Omura's whale. Phylogenetic analysis of mitochondrial control region sequences from the whale against other reference baleen species showed our specimen nested within sequences from Omura's whale with high bootstrap support and was clearly separate from sequences of Bryde's whale, thus confirming the limited morphological identification of the specimen as Omura's whale. The carcass was in good condition with no obvious signs of trauma, and assessment revealed the animal was recently deceased. Lack of decomposition and no injury suggested it was likely to have been alive at the time of stranding and to have been occupying inshore waters prior to being washed ashore. Confirmation of an Omura's whale in Western Australian waters extends knowledge of its distribution southwards in the eastern Indian Ocean, suggesting further survey in these waters may provide more information on this poorly known species.