Bollo58's picture

Common Dolphins - Sennen Cove

Observed: 18th July 2013 By: Bollo58Bollo58’s reputation in MammalsBollo58’s reputation in MammalsBollo58’s reputation in Mammals
Common Dolphins - Sennen Cove
Common Dolphins - Sennen Cove
Description:

Watched pod of about 8 - 12 animals for about 30 mins moving around the bay at Sennen Cove

Identifications
Species interactions

No interactions present.

Comments

the naturalist man's picture

Dolphins

From the photos I've got to agree with Gill, you can not tell the species.

Indeed, this photo illustrates a problem with dolphin ID from photos; the angle of the dolphin to the camera.

I think it is safe to presume these are all the same species, though you can get mixed groups. That said, the left animal has a deeply curved fin, coming to a sharp point, suggestive of white-beaked dolphin; the middle one looks to have a very shallow curved fin, more like a common dolphin; and the right hand one appears to have a very blunt tip to its fin as in bottlenose dolphin.

Have we three species swimming together or is it a trick of the camera angle?

Graham Banwell

Visit the iSpot Yorkshire forum for information on events, issues and news relating to 'God's own country'
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james spencer's picture

Dolphins

These species would not swim together. Bottlenose would attempt to predate common. Almost certainly white-beaked. The strongly falcate fin is too extreme for other species whilst the other fins fit into the range of white-beaked. Only thing missing is the pale sadle but that is likely lost with the lighting.

Gill Sinclair's picture

Interactions between species

Although bottlenose dolphins do have a reputation for being bullies, predation on other cetacean species appears to have quite a strong cultural element to it (in the same way that different orca populations develop very different feeding habits which are passed along generations). For example I believe the bottlenose dolphins in the Moray Firth have been observed killing and injuring harbour porpoises (although I don't know if they've ever been seen actually eating one), whereas I saw mixed groups of dolphins including common + bottlenose in the Straits of Gibraltar.

Gill Sinclair
OU Certificate in Contemporary Science
www.gillsinclair.net
Twitter @Gill_Sinclair

the naturalist man's picture

Dolphins

I think you misunderstood my point, I was not seriously suggesting we have three species but that camera angles can distort fin shape and therefore you can not be absolutely sure which species we have based on the photo.

Graham Banwell

Visit the iSpot Yorkshire forum for information on events, issues and news relating to 'God's own country'
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trudy-russell's picture

just to be controversial from

just to be controversial from my knowledge of the area and the number of animals activity I would suggest perhaps bottlenose. We have a local pod that moves along the coast up to north Devon of about 10 - 14 animals. White beaked are extremely rare in this area and had they spent any time the number of local observers would most likely have spread the word! There have been records of Rissos in the area recently however. no firm help I realise but very interesting sighting whichever species

Trudy Russell
Marine Advisor
Natural England

To find out about what's going on in the south west check out http://www.ispot.org.uk/forum/8409

the naturalist man's picture

Dolphins

Trudy's comments highlight once more how difficult fins can be from photos if they are not at 90 degrees to the camera and/or more of the body is showing.

They are definitely not Risso's as the base of the fin is clearly too broad, even assuming the light has made the mid-grey of their bodies look black.

Graham Banwell

Visit the iSpot Yorkshire forum for information on events, issues and news relating to 'God's own country'
http://www.ispot.org.uk/forum/8411

Bollo58's picture

Dolphins - further discussion

Since my original post I have reported my sighting to the Sea Watch Foundation & have sought additional expert identification opinion from it's Director - Dr Peter G.H. Evans. I have made him aware of all the above gratefully received contributions & he has responded as follows:

"Some of the comments you've received are fair ones, but others are incorrect I'm afraid. It is certainly true that single photographs can be misleading if the angle to the sighting is acute. However, at least two of the animals have been photographed more or less at right angles, and the fin of one of these at least is too tall, slender and upright to be common dolphin. Although there is no sunlight on the fins, they are very dark. All these features fit white-sided dolphin or white-beaked dolphin rather than common, bottlenose or Risso's. White-beaked dolphins usually have a larger, broader fin than the one at the back in the photo. Contrary to one of your contributors, mature Risso's dolphin can have very slender tall falcate fins but those individuals are generally rather pale and I think that would probably show up in the picture.

Although it's worth keeping in the back of one's mind the normal status of each species in the area, all of these species have been recorded in Cornish waters, some more commonly than others. One of your contributors considered white-beaked very rare. It is quite rare in the region but occurs regularly not so far away around Lyme Bay on the South Devon coast (and has ranged throughout the Channel). White-sided dolphins are actually rarer here but again have been seen on occasions. The commonest species in the area is common dolphin followed by bottlenose and then Risso's. But identification should never be made on this basis. As for mixed groups, all of the above species can be seen on occasions in mixed species groups (in fact I've seen every such combination myself). However, I don't see any evidence for there being more than one species here.

From the two pictures alone, one cannot say categorically what species it is, but as I stated earlier, it looks most like white-sided dolphin. Feel free to relay my remarks if it helps".

the naturalist man's picture

Dolphins

Thanks Bollo58, it's always good to have specialist advice; I refer to others for advice when I'm not sure.

Based on Peter's comments please put up an identification of White-sided dolphin, though I suggest you give it a 'not certain' level of confidence.

Graham Banwell

Visit the iSpot Yorkshire forum for information on events, issues and news relating to 'God's own country'
http://www.ispot.org.uk/forum/8411

Bollo58's picture

Dolphins - update identification

Thanks Graham & everyone else for your input.

Hopefully next time I spot some dolphins I can get clearer pics which may make identification somewhat easier !!

the naturalist man's picture

Photogenic dolphins

Just getting photos of dolphins can be hard enough!

Graham Banwell

Visit the iSpot Yorkshire forum for information on events, issues and news relating to 'God's own country'
http://www.ispot.org.uk/forum/8411

james spencer's picture

I can see why White-sided are

I can see why White-sided are suggested and from a purely ID point of view it would be the parsimonious answer however due to the scarcity of these animals in the south-west and the non-commital nature of the ID from an expert (which to me sounds like 'Im not sure but I will have a punt') surely dolphin sp is what should be promoted as the likely ID. I am aware that earlier in the piece I railed for White-beaked as White-sided didnt really come into my thinking. I was under the impression that the objective here was getting organisms to their lowest identifiable taxon not taking a punt which seems to be what Graham is suggesting.

Gill Sinclair's picture

Dolphin species

Hi James - iSpot users do take different approaches where the ID is uncertain. My usual approach is the one you suggest - I try to make an "I'm as sure as I can be" ID even if that's only at genus or family level. But another approach is to make an "It's likely to be this, but I can't be certain" ID to see what other users think - I did that recently where I thought a shrew might be a greater-white toothed shrew, but I don't often do that.

I understand from Graham that, once an ID is agreed with by someone badged as an Expert, it goes onto the NBN database as a record, so now that I'm badged 'Expert' I feel I have an additional responsibility to only agree with IDs that I'm certain about:-) For that reason I'll be sticking with my original ID of "Dolphin species" because although all of the comments have been interesting, nothing in them has made me any more certain about the ID for this sighting.

I think having all these suggestions and comments does make for an interesting discussion and a way for us all to learn more about identifying dolphins (and the difficulties of doing so!).

Gill Sinclair
OU Certificate in Contemporary Science
www.gillsinclair.net
Twitter @Gill_Sinclair

the naturalist man's picture

Dolphins

Hello James
I fully understand your confusion about my comments above. I asked for the identification to be put up simply because of the discussions here. However, you will note I'm still agreeing with dolphin sp. as I am not personally happy with any other identification. As Gill says this has been an interesting discussion on dolphin identification.

Graham Banwell

Visit the iSpot Yorkshire forum for information on events, issues and news relating to 'God's own country'
http://www.ispot.org.uk/forum/8411