Friday, 24 February 2023

Indian Ocean Humpback Dolphins, Munamban, Kerala, India


At Munamban harbour today we saw at least 10 Indian Ocean humpback dolphins. These wonderful animals are closely related to the Australian humpback dolphins that I saw in 2018 and are just magical and enigmatic. They are pale grey in colour with a white / pinkish tip to the dorsal fin and instantly identifiable. Or so it would seem....

There is considerable uncertainty surrounding humpback dolphins in the Indian Ocean. Animals on the west coast of India (including Munamban) are thought to be Indian Ocean humpbacks, whilst those on the east coast are thought to be a different species, Indo-Pacific humback dolphins. However there is also a sub-species of Indian Ocean humpbacks, ssp. lentiginosa, which occurs on the east coast in the Bay of Bengal, which may in fact be a third species (Carwardine 2020).

So based on location it seems pretty clear, these must be Indian Ocean humpbacks? Well possibly... there are a few problems though. In the field it was immediately clear that there were two different colour types present the first was pale grey as in the animal at the top of the post, but the others were dark grey almost brown in colour, as is the case with animal below.


There's obviously a clear difference in colour. Also on closer inspection the darker animals have a much more prominent dorsal hump.


This isn't in shadow, the sun was behind me when I took this photo, and other dolphins in the same area were clearly pale grey, and look at that hump!


Note the lack of a hump on this animal compared to the darker animal above. This animal is closer but I was standing in the same spot so the light was the same.

So what does all of this mean? Indian Ocean humpbacks are much darker with much more prominent humps than Indo Pacific, which are pale grey with whitish or pink blotches on the dorsal fin and body. It would appear from my photos that both species were involved in todays sighting, but I don't have enough knowledge of variation in these dolphins to be sure of that. 

Another spanner in the works is that Indian Ocean humpbacks ssp. lentiginosa  are pale grey and have a less prominent hump, more like Indo-Pacific. However they apparently only occur in the Bay of Bengal so I'm not sure what the likelihood is of them occurring at Munamban, probably less chance than Indo-Pacific I would have thought.  


Whatever the truth is, it was a wonderful experience to see them swimming in the harbour around the Chinese nets.




I mean that's not just pale, it's almost white.


I love these fishing boats...

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