Abstract
Blue whalesBalaenoptera musculusin the Indian Ocean (IO) are currently thought to represent 2 or 3 subspecies (B. m. intermedia, B. m. brevicauda,B. m. indica), and believed to be structured into 4 populations, each with a diagnostic song-type. Here we describe a previously unreported song-type that implies the probable existence of a population that has been undetected or conflated with another population. The novel song-type was recorded off Oman in the northern IO/Arabian Sea, off the western Chagos Archipelago in the equatorial central IO, and off Madagascar in the southwestern IO. As this is the only blue whale song that has been identified in the western Arabian Sea, we label it the ‘Northwest Indian Ocean’ song-type to distinguish it from other regional song-types. Spatiotemporal variation suggested a distribution west of 70°E, with potential affinity for the northern IO/Arabian Sea, and only minor presence in the southwestern IO. Timing of presence off Oman suggested that intensive illegal Soviet whaling that took 1294 blue whales in the 1960s likely targeted this population, as opposed to the more widely distributed ‘Sri Lanka’ acoustic population as previously assumed. Based upon geographic distribution and potential aseasonal reproduction found in the Soviet catch data, we suggest that if there is a northern IO subspecies (B. m. indica), it is likely this population. Moreover, the potentially restricted range, intensive historic whaling, and the fact that the song-type has been previously undetected, suggests a small population that is in critical need of status assessment and conservation action.
Highlights
Resolving the taxonomy and population structure of baleen whales remains an essential process in Endang Species Res 43: 495–515, 2020 depending on scientific opinion, with distinctions based on morphology, genetics, acoustics, and known distribution
Leroy) upon viewing the song-type in Cerchio et al (2018), prompting a review of 4 yr of data from the DGN and DGS recording sites. As these recorders were placed at the depth of the sound fixing and ranging (SOFAR) channel, the detection range was likely the largest, and some of the cleanest examples of the song were recorded, albeit still at a predominantly low signal to noise ratio (SNR)
Sei Balaenoptera borealis, Antarctic minke and common minke B. acutorostrata ssp. whales have not been confidently reported off Oman or in the Arabian Sea (Baldwin 2003, Minton et al 2010), and their known vocal repertoires are distinctly different from this novel song-type (Watkins et al 1987, Gedamke et al 2001, Calderan et al 2014, Risch et al 2014)
Summary
Resolving the taxonomy and population structure of baleen whales remains an essential process in Endang Species Res 43: 495–515, 2020 depending on scientific opinion, with distinctions based on morphology, genetics, acoustics, and known distribution. These include the Antarctic blue whale B. m. Brevicauda Ichihara, 1966, the northern Indian Ocean blue whale B. m. The most widely accepted taxonomic division is between the Antarctic blue whale and the pygmy blue whale subspecies, supported by morphological and distributional differences (Branch et al 2007a,b, 2009). Indica, as opposed to a regional population of pygmy blue whale, is debated and without scientific consensus The classification of a northern Indian Ocean population as a separate subspecies, B. m. indica, as opposed to a regional population of pygmy blue whale, is debated and without scientific consensus
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
