Identification help with a cetacean photographed off Sri Lanka

These photos of a mother and young cetacean were taken off Sri Lanka on the usual Blue-Whale-watching boat trip off Mirissa in April 2015. The boatmen said they thought they were Short-finned Pilot Whales. But they appeared to be more-or-less the size of Spinner Dolphins whereas the Pilot Whale is much larger.

I now think they may have been Dwarf Sperm Whales based on the 45°slope of the leading edge of the dorsal fin (unlike the similar-sized Pygmy Killer and Melon-headed Whales) and the peculiar tip of the dorsal fin , as well as the long, straight back in front of the dorsal fin and slight angle between the back and what appears to be the back of the head. This is consistent with their floating with dorsal fin and front part img_1789 img_1787

of back exposed, and having disappeared by sinking into the water.

Would someone with experience in cetacean identification please help me confirm or discard this tentative identification?

Héctor Gómez de Silva

Mexico City

 

9 Comments
  1. Profile photo of Jon Hall
    Jon Hall 7 months ago

    Hi Hector, I have not seen this species but I know Fiona Reid saw them off of Sri Lanka in 2012. I think you are probably correct in your ID. But I am not an expert!

  2. Profile photo of Jon Hall
    Jon Hall 7 months ago
  3. Profile photo of hectorgom Author
    hectorgom 7 months ago

    Thank you very much, Jon. The fin shape and straight back and head, with a tiny dip in between back and head, support the id as Dwarf Sperm Whale, and the fact that this species was seen off Sri Lanka in 2012 is supportive.
    Does anyone else have something to add that may evidence for or against this identification?
    Gratefully,
    Héctor

  4. Vladimir Dinets 7 months ago

    It is definitely a Kogia. They mimic large sharks, and their dorsal fins look very shark-like. But to me it looks more like pygmy sperm-whale. Both species are present around SL and probably common (I saw one pygmy sperm whale off Negombo in August 2013). They look very similar, but in pygmy the dorsal is usually more sloped and located almost 2/3 of the way between nose and tail, not halfway. On the other hand, the dorsal is a bit large for pygmy. Do you have any photos where the tail is visible?

  5. Profile photo of hectorgom Author
    hectorgom 7 months ago

    Vladimir
    Thank you very much for your feedback. Unfortunately, no photos where any more of the creature is visible, nor were we able to see any more than the dorsal fin and the top part of the creature ahead of that.
    The only references I have are 1) Handbook of Mammals of the World, which features a couple of photos of Dwarf Sperm Whale which I think are a very close match to the adult from Sri Lanka, 2) the article linked in the reply from Jon in which the slope of the fin is also a close fit but more especially which states and shows photos of Pygmy Sperm Whale with a slight hump on the back (which my Sri Lanka whales definitely do not have); and 3) (thanks to Google Books) the relevant pages of Jefferson et al. Marine Mammals of the World: a comprehensive guide to their identification, which mention the larger dorsal fin and flat back of Dwarf Sperm Whales as a distinction from Pygmy Sperm Whales (but also say that dorsal fin size and position is variable and so in many cases at sea sightings of Kogia may be unidentifiable.
    I do feel that my photos (actually, my wife did the photography) more closely resemble Dwarf.
    But I do not have access to Shirihai and Jarrett’s more recent book, which may clarify the case.
    Saludos,
    Héctor

  6. Vladimir Dinets 7 months ago

    I showed the photos to Bill Lanier who has seen both species as strandings and also at sea, and he thinks it’s dwarf with 80% certainty 🙂

  7. Profile photo of hectorgom Author
    hectorgom 7 months ago

    Vladimir
    Thank you very much!
    I am feeling a little sheepish, but I just found out why I did not take any photos of the cetaceans whereas my wife did: because I took video!
    The video shows that at first there were 2 adults, but one dove soon after the encounter, the other floating with the young for several seconds before diving in. The second adult eventually sank into the sea but the young rolled in, showing the tail! I was able to make measurements of the young one on my computer screen by freezing the image in the critical moments, and these revealed that the front of the dorsal fin was less than 50% of the total length, adding further evidence that they were Dwarf Aperm Whales! Hurray, I am so glad I took that video!
    Saludos,
    Héctor

  8. Vladimir Dinets 7 months ago

    Cool, that might be the only video of this species in the wild.

  9. Profile photo of hectorgom Author
    hectorgom 7 months ago

    Jon Hall tells me that he has seen another video of this species, so mine is not the first but it may be one of the first. Here is a link to the video on YouTube:

    https://youtu.be/6bUnZoVQAFo

    Enjoy!

    Thanks Jon and Vladimir!

    Saludos,
    Héctor
    Mexican birdwatcher with occasional forays into mammal watching

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