On December 21st, 2019, scuba divers near Netrani Island off the west coast of India (State of Karnataka) encountered something extraordinary while travelling to their dive site: a humpback whale. The dive masters from Dive Goa, Absolute SCUBA India and West Coast Adventures knew this sighting was special, because they had all been in contact with Dipani Sutaria, who had travelled along India’s west coast from 2016 onward raising awareness of the Endangered status of Arabian Sea humpback whales, and the value of documenting their presence. Seemant Saxena from Absolute SCUBA India and Paritosh Agarwal from Dive Goa entered the water, free-diving through the murky depths to capture a few seconds of underwater footage of the whale to share with Dipani.
Dipani immediately shared this footage with her colleagues working with humpback whales on the other side of the Arabian Sea. She hoped that they would be able to discern some features of the whale in the video that would allow them to identify and match it to one of the individual whales catalogued through 20 years of photo-identification work in Oman. Had it been any other whale, the matching exercise would have been futile, as the water was filled with plankton, and the whale’s features were not very clearly visible. What was visible was a large, white U-shaped scar over the top of the whale’s back, another white scar on the tail fluke where it joined the whale’s trunk, and, as the team peered more closely through the milky water in the video, it seemed that this whale was missing most of the left side of its tail fluke.
Only one whale in the Oman catalogue fit this description – Individual OM11-010, a whale observed and photographed on two consecutive days in October 2011 in the Gulf of Masirah. Careful comparison of all the available photos of this whale with the whale in the Netrani video revealed more similarities, including more scars and the distinctive notches on the trailing edge of the tail fluke. The international team of five experienced researchers concluded with certainty that that this must be the same whale.
‘This is a hugely exciting finding.’ says Andy Willson from Five Oceans Environmental Services, lead scientist on whale surveys conducted on behalf of the Environment Society of Oman. ‘Firstly it confirms that OM11-010 is still alive, despite the severe injuries we first documented over 8 years ago. Secondly, it provides further evidence that Endangered Arabian Sea humpback whales are moving between Oman and India’. Trans-Arabian-Sea movement was first documented in November 2017 when a female whale that was satellite tagged off the coast of Oman journeyed to the Southern tip of India and back to Oman again.
However, the sighting is also a sobering reminder of the threats that Arabian Sea humpback whales and other whale and dolphin species face in the Arabian Sea and around the world. Arabian Sea humpback whales are distinct in that they don’t migrate long distances between tropical breeding grounds and polar or temperate feeding grounds. Instead they remain in the Arabian Sea year-round. Genetic, acoustic, and photographic evidence shows that the population is isolated from neighbouring populations in the Southern Hemisphere, and that fewer than 100 whales are present off the coast of Oman.
Expert analysis of high resolution images of OM11-010’s injuries indicate that they were caused by entanglement in fishing gear. The phenomenon has been documented in other humpback whale populations as well, and leaves tell-tale signs. The scars on the remaining half of OM11-010’s tail show where a rope or net was tightly wrapped around the fluke in a pattern symmetrical to the line of amputation of the missing fluke. Scars on the whale’s back and flank show where a rope was so tightly wrapped over the dorsal fin that it cut into the whale’s skin and muscle and left a deep and lasting deformity. Studies of different humpback whale populations around the world indicate that the proportion of whales bearing signs of fisheries entanglement can range from 16% in the Gulf of Maine1, to 25% in Iceland2, and as high as 70% off the coast of Alaska3. These statistics only represent the whales that survive their entanglements. Bycatch in fishing gear is known to be the biggest threat to marine mammals around the globe, causing an estimated 600,000 deaths annually4.
Teams on both sides of the Arabian Sea are working hard to protect whales from entanglement and other threats by studying their distribution and behaviour and working with relevant authorities to put protection measures in place. As part of a long-term study funded by the International Whaling Commission, Sutaria and her colleagues have recently deployed two passive acoustic recorders that will record humpback whale and other marine mammal vocalizations off the west coast of India and provide more insight into when and where whales are present there. The Indian Ministry of Environment, Forests and Climate Change has listed Arabian Sea Humpback Whales as a priority endangered species for Recovery, has endorsed a Concerted Action under the Convention on Migratory Species, supported the proposal for a Conservation Management Plan under the International Whaling Commission, and has provided funding to the Karnataka State Forest Department for an Arabian Sea Humpback whale research and recovery program.
Willson and colleagues from the Environment Society of Oman and other organisations around the world are adding new and exciting techniques to their 20-year-long study of humpback whales off the coast of Oman, including the use of drones to measure body condition and health.
This recent finding is an excellent example of the need for continued and increased regional collaboration to better understand and protect this Endangered population of whales.
Additional information can be found on the following websites:
Arabian Sea Whale Network website: https://arabianseawhalenetwork.org/
IUCN Red List Assessment for Arabian Sea humpback whales: https://www.iucnredlist.org/species/132835/3464679
The Environment Society of Oman’s Website: http://www.eso.org.om/index/list3.php?categoryId=339
Five Oceans Environmental Services: https://www.5oes.com/
Marine Mammals of India Website: http://www.marinemammals.in/mmi/
For more information contact:
Dipani Sutaria: firstname.lastname@example.org
1 Robbins, J. Scar-based inference into Gulf of Maine humpback whale entanglement: 2010. Report to the National Marine Fisheries Service. Order number EA133F09CN0253 (2012).
2 Basran, C. J. et al. First estimates of entanglement rate of humpback whales Megaptera novaeangliae observed in coastal Icelandic waters. Endangered Species Research 38, 67-77 (2019).
3 Neilson, J. L., Straley, J. M., Gabriele, C. M. & Hills, S. Non‐lethal entanglement of humpback whales (Megaptera novaeangliae) in fishing gear in northern Southeast Alaska. Journal of Biogeography 36, 452-464 (2009).
4 Read, A., Drinker, P. & Northridge, S. P. Bycatch of Marine Mammals in U.S. and Global Fisheries. Conservation Biology 20, 163-169 (2006).