jason.birt's picture

Dolphin stranding

Observed: 11th October 2008 By: jason.birtjason.birt’s reputation in Mammalsjason.birt’s reputation in Mammals
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Description:

I was wondering about adding this observation because it involves a dead observation rather than a live observation. If this is moderated off then I understand. I was called out to this (originally live) stranding and arrived with others present. We decided to bring it in to send it off for autopsy. The reason I'm posting this is because this stranding was not due to human factors but instead bears all the hallmarks of bottlenose dolphin violence, which, I hope, the photos evidence. People more expert than me suggest that the rake marks are the correct spacing for bottlenose teeth. As for ID, at the time everyone agreed it was a common dolphin but looking at the photos, I'm not so sure. The "hour glass" isn't very obvious but a white stripe is... Over to you...

Identifications
Species interactions

No interactions present.

Comments

lst55's picture

Bottlenose?

Looks more like bottlenose from the pictures I've seen but I'm no expert either!

Strandings are so sad, but it is a relief to know this one wasn't caused by human activities, unlike so many mass dolphin strandings and whale strandings. We really need to stop messing with sonar in the oceans!!

Lucy

OU Student

greenman's picture

Posting of dead observations

Jason, personally speaking I think you were absolutely correct to post this. I view iSpot as a website where I can learn about wildlife and the information you included with your posting regarding the reasons for the stranding I found very informative and interesting.
Regards

greenman

Jonathan's picture

I would agree. We have had

I would agree. We have had quite a few images of dead animals and there is no sense in ignoring the fact that sometimes this is what we see. These images often give information on the cause of death, which is valuable too.

If you prefer not to show an image (for example of a messy road kill), an observation can still be made without a photo.

Jonathan
University of Edinburgh and Biodiversity Observatory (OU)

the naturalist man's picture

Dolphin

This is a fantastic posting, thanks. The marks in the two right hand photos do look like tooth marks and as bottlenose dolphins are the most agressive it is likely to be them. Risso's dolphins fight amongst themselves (hence the distinctive scars on their bodies), but I do not know of them attacking other species.

It would not be shark or killer whale, the only other two animals likely to take on a dolphin, as they bite down and rip, not scrape.

The marks are not consistant with propellor blade cuts as they almost always cut deep, going through the skin into the blubber.

However, that said, what are the marks in the top left photo? They are definately human created. They look like the imprint of something with regular spaced bars like a grill - the oval shape is due to the shape of the dolphins body as it has pressed against something.

I am also sorry to spoil your opinion that this is a natural death as those scars are not enough to have killed this dolphin; I've seen living dolphins, and seals, with gaping wounds where the blubber has been showing through. I've then seen them the next year with nothing more than a scar. Superficial cuts like these would be hardly noticed by a dolphin. Only an autopsy would tell us if it also has internal damage and hopefully what caused it. were there other marks etc. which indicated a non-human cause of death?

As far as the species, it is a common dolphin, the wavy pale line down the side is the indicator here. It is 'washed out' due to being dead, however, I'd still expect to see a reminant of the stripe going from the head to the dorsal fin if it were a striped dolphin and the dorsal fin and muzzle are wrong for bottlenose.

Note, I have no problem with photos of messy roadkills. Often such bodies are the only indication of the presence of a species in an area. However, please restrict such photos to potentially rare species!

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

jason.birt's picture

Clarification

Thanks for all the comments! Good to see the post has generated debate. The ID is definitely Delphinus delphis - my colleague's contact at the VLA (Veterinary Laboratories Agency) undertook the autopsy, a point that I didn't make clear in the earlier posting, and ID'd the animal as such. The cause of death was established at the autopsy but I haven't seen the report. It was very rough that day and the juvenile was trapped within the bay with a boulder-strewn shore so it is likely that the animal, possibly exhausted by its tussle with bottlenose dolphins (the bottlenose rake marks are fresh), could not escape and got battered on the rocks and drowned. The original call out was for a live animal. Incidentally, this animal was feature in a research paper on bottlenose violence.

Jason Birt

the naturalist man's picture

Dolphin

I would be interested to know what the autopsy does say was cause of death. I agree, the animal could have been exhausted, and possibly in shock, then stranded as a live animal and died ashore. I am still puzzled by the marks in teh first photo, they are definately from a man-made object. Was it lieing on any kind of grill at any time?

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

jason.birt's picture

I'm still chasing up the

I'm still chasing up the research report in which this animal featured. The grill mark I'm not sure about. It wasn't found on a grill - granite rocks instead. Some people at the time think it was a healed scar from a previous dolphin attack, although it does look rather too regular for that...

Jason Birt

the naturalist man's picture

Dolphin

It is definately not the scar from an animal attack of any kind; nothing would leave such regular markings. It almost looks like a boot print as though someone stood on the animal without putting their heal down. Without seeing it I can not be sure but I doubt it is old scar tissue as I would expect signs of tearing at the edges of the white bands, it's more like an imprint than a scar. If you press down on the skin of a corpse shortly before rigur mortis then the imprint will stay leaving this sort of mark. Lets hope the autopsy report comments on it. Can you remember how big it was, and on what part of the body?

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

dw5448's picture

Remember bycatch

Bycatch in fishing nets is still the greatest cause of strandings, though usually for dead animals. It is less likely that animals would be found soon enough to be released alive but weakened, so it seems a bit odd. Bottlenose attacks will show broken ribs and significant internal bruising usually inflicted by a snout (tooth marks are more often about dominance and sexual rivalry). To me, the lacerations seem too deep and too irregular to be due to tooth raking. Bottlenose are nasty beasts and if they want to harm anything they tend to give it a good thumping interspersed with tosses in to the air.

In terms of ID, it isn't a bottlenose because the melon (forehead) isn't bulbous enough and the beak is too long, giving the overall pointed effect - think of Flipper, who would also be significantly bigger and bulkier. As stated above, post-mortem changes frequently mean the characteristic hourglass pattern disappears and the buff colour fades so that a grey countershaded effect sets in. If you look at illustrations of common dolphins, there is often a line or two nearer the ventral surfaces, though these are less noticeable in fast action viewing. Interestingly, you don't often see the stripes of the Striped as they whizz along and leap high, though occaionally you may just see the "lock of hair" effect just behind the head.

If you are interested in strandings, why not have a look at the strandings section on www.iwdg.ie for comparisons.

Dave

the naturalist man's picture

Common dolphin

I'd stick with common dolphin rather than striped due to the wavy line down the side and the lack of a dark ring around the eye which I'd expect in striped dolphin.

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