New papers highlight the unique and vulnerable status of Arabian Sea humpback whales and the results of satellite tagging of whales in the Indian Ocean

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Figure from Kershaw et al. 2017 demonstrating how Arabian Sea humpback whales were the  most genetically differentiated among the 7 breeding stocks sampled in the study.

Recently two scientific papers have been published that are of great value to our understanding of humpback whales in the Indian Ocean and Arabian Sea.  The first is a review of 3575 genetic samples collected from seven breeding stocks of humpback whales in the South Atlantic and Indian Oceans.  The study titled “Multiple processes drive genetic structure of humpback whale (Megaptera novaeangliae) populations across spatial scales” was published in Molecular Ecology.   One of the largest genetic studies ever conducted on humpback whales for the purpose of clarifying management decisions, it revealed more connectivity between the breeding stocks on the east and west sides of the African continent than expected.  Conversely. the results indicate that the Arabian Sea humpback whale population (ASHW) is the most highly genetically differentiated across all indices and partitions.  The paper uses samples collected off the coast of Oman in 2001 and 2002, and places them in a wider context than some of the previously published papers using these same samples.  The wider comparison confirms the unique and precarious nature of Arabian Sea humpback whales, and the authors recommend that the small population numbering fewer than 200 whales be made a conservation priority. The paper has been highlighted in  Science Daily  and Tech Times.   A full PDF of the paper can be downloaded here.

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Figure from Cerchio et al 2016, showing tracks of humpback whales satellite tagged off two sites in Madagascar. Note the unexpected movement of one whale to a position north of the Equator off the coast of Somalia.

 

The second paper of note is titled “Satellite telemetry of humpback whales off Madagascar reveals insights on breeding behavior and long-range movements within the southwest Indian Ocean“.  Published in the Marine Ecology Progress Series, it reports on the results of  23 humpback whales that were satellite-tagged off the northeast and southwest coasts of Madagascar during peak breeding season.  The study reveals interesting sex differences in the behaviour of tracked whales, and indicates that there may be less mixing between the two study sites in Madagascar than would previously have been assumed. Of particular interest for the ASWN, is the track of one individual that moved north from the tagging site off Madagascar, crossing the equator and reaching the coast of Somalia before the tag stopped transmitting at 2° 59.9’ N. During 32 days the male whale covered over 2800 km (over 3120 km of trackline).  Given the genetic evidence showing a lack of mixing between humpback whales in the Southern Indian Ocean  and the Arabian Sea, the authors suggest that this whale may be a “vagrant” or that its movements may represent a new wave of northward exploration and possible expansion taking place as Southern Hemisphere populations increase following the cessation of whaling. A full PDF of the paper can be downloaded here.