Ocean News

The Sharpnose Conundrum

27th August 2008

So it’s been a while since the last update.  Finally, last Thursday, the wind from TS Fay abated a little and we were able to get back to our sampling.  We were fishing the wall zone where historically our highest catches have been so we were pretty sure we would see sharks.  Our record so far this project was sixteen sharks from four species on a single longline set – that was a busy day!  As expected we caught few sharks, thirteen to be precise, of which only one was a Caribbean reef and the rest were all sharpnose sharks, ten Atlantic and two Caribbean – I think!  A new record for the largest number of a single species on a set!

The Bahamas is an interesting place to look at sharpnose sharks.  It is reportedly the only place in the world where the home range of the Caribbean sharpnose and the Atlantic sharpnose overlap and as such we are probably the only shark research program in the world that catches both on the same longline.  Which raises a problem – telling the two apart.

The literature offers fairly generic descriptions of the two species, enough to separate them from other species but not from each other.  Visually they are obviously different species, slightly different second dorsal positioning, body color and size but descriptions in the literature and not specific enough to make a positive identification without making vertebral count…. not an easy thing to do if you want to make an ID in the field and release the shark unharmed!

Anyhow – we have a plan.  Every shark we catch has a genetic sample taken which is given to our collaborators at the Guy Harvey Research Institute. They will be able to make a positive ID from a 2mm circular punch taken from the dorsal fin and that coupled with our morphological observations should solve the sharpnose conundrum – although I don’t think it’s a problem for most other shark research programs!

I don’t have any photos of the two species side by side just yet so here is a screen grab of an Atlantic sharpnose taken from one of our baited underwater video surveys.