Tuesday, July 09, 2013

Fiji: new Shark Record?

Pic by John Philp - click for detail.


A surfer sent me this pic a few years ago.
It's from a surfing event in the mouth of the Sigatoka River, and the description that came with it was
Attached pic of one of the sharks from that contest in 2007 (May 5th) at the Sigatoka Riverrmouth, attached surfing pics show the clear water on the incoming tide then it becomes progressively brown with the outgoing tide and then the sharks appeared - predictably.

This was the same time I saw the sharks doing acrobatics in the river, maybe shedding remora's? I don't know. They really looked like dolphins playing. Bizzare.
You're going to think I'm delusional but I recall the sharks being about 4 or 5 feet long, and bizzarely they were spinning not only on their axis but also end over end forward like dolphins do, and they were not dolphins! I have to ask someone else who was there four years ago to see what they remember.
My first thought was Spinner Shark.
But having checked, they don't feature on the infamous Seeto list, and the IUCN doesn't list Fiji among its range - and so I opted for the common Blacktip that is both present here and also engages in leaping and spinning, this mostly when preying but possibly also in order to dislodge remoras.

But I may have been mistaken.
We've been recently engaged in a rather epic research project investigating Fiji's coastal Shark fishery, and I've just received the first DNA analyses of fin samples from the local Fish markets - and imagine my surprise at discovering an (undoubtedly correct) record of Carcharhinus brevipinna!

Regarding the Sigatoka, we'll of course never really know.
Both hypotheses are plausible - but my gut tells me that it was a Blacktip, this owing to the rather large black marking on the first dorsal as opposed to the rather inconspicuous one on the Spinner.
JSD? David?

Anyway, all very interesting!
This will undoubtedly lead to a publication, possibly lumped together with several other discoveries and range extensions we've recorded over the years.

Keep watching this space!

PS more evidence + a comment by John Philp here!


jsd said...

I agree with your polytomous starting point. It is definitely possible that the most parsimonious presumption is limbatus; if not, the most probable alternative is presumably brevipinna (though the use of 'most' is probably unnecessary) though both possibilities are indeed unprovable.

Or the frond of a coconut tree.

OfficetoOcean said...

My first thought also was Spinner but that dorsal fin is more in keeping with the Blacktip. Interestingly (or not) Spinners are regularly reported exhibiting that exact same behaviour in Florida when chasing baitfish in those same conditions and particularly in shallow water.

That said I see no reason why it could be discounted that Blacktips would do similar so judging by the size if that fin I'd go for Blacktip with a caveat that if it were a Spinner I would not be surprised.

Been trying to think of alternatives but I can't get away from those two.

DaShark said...

Crikey - polytomous???
Are you trying to dazzle us with brilliance?

But since you insist - with only two likely candidates, wouldn't it have been more parsimonious (literally!) to have used dichotomous?

Detail detail! :)

jsd said...

I was keeping the possibility of a wayward tilsoni under my hat.

DaShark said...

Touché would have sufficed!

And at the risk of being called pedantic, again - it's tilstoni with a "t"!

Detail detail! :)

jsd said...


Shark Defenders said...

There are some great photos of spinners and surfers from New Smyrna.