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.
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