Dans l'océan indien, l'étude d'un type de chant inconnu met en lumière l'existence d'une population de rorquals bleus ignorée en tant que telle jusqu'à présent. Sa zone de distribution se situe dans la région occidentale de l'Océan Indien ( de la mer d'Oman, au large du sultanat, au canal du Mozambique à l'ouest de Madagascar, en passant, dans sa partie centrale, par l'archipel des Chagos). Jusqu'alors, on classifiait les Rorquals bleus de l'Océan Indien en 3 sous-espèces, structurées en 4 populations. Voir le détail dans l'étude publiée dans "Endangered Species Resarch" :
S Cerchio, A Willson, EC Leroy, C Muirhead, S Al Harthi, R Baldwin, D Cholewiak, T Collins, G Minton, T Rasoloarijao, TL Rogers, M Sarrouf Willson. A new blue whale song-type described for the Arabian Sea and Western Indian Ocean. Endangered Species Research, 2020; 43.
ABSTRACT: Blue whales Balaenoptera musculus in 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.
Voir aussi le commentaire détaillé dans "Science Daily", hier :
New England Aquarium. "New population of blue whales discovered in the western Indian ocean." ScienceDaily. ScienceDaily, 21 December 2020.