Thursday, October 9, 2008

Our first whale shark copepods!

When Mark Meekan from AIMS in Darwin asked us to keep an eye open for copepods on whale sharks we thought he was kidding as none of us had noticed them on any of the sharks we have here… but going through some front-on images (photo left by Tony Baskyfield) it seemed that they may in fact be on Seychelles whale sharks too.

Copepods are small crustaceans and the ones found on whale sharks look a bit like miniature horseshoe crabs. They are not parasites as such but can be considered more as commensals because they feed on algae and bacteria that grow on the whale shark's skin. The ones found on whale sharks (Pandarus rhincodonicus) are apparently only found on whale sharks and they aren’t able to move very far themselves and so get carried from place to place by their host shark.

Because whale sharks breed slowly, probably taking some 20 years to reach maturity, their genetic differentiation can be masked by the fact that sharks from different areas can move very large distances during their lives. By comparison, their hitch-hiking copepods breed rapidly and as they only occur on whale sharks their DNA can be used as a biological marker tag to differentiate between populations of whale sharks that visit different areas….. If copepods here in Seychelles have the same DNA markers as those from East Africa then it would indicate that the Seychelles sharks also visit East Africa, or vice versa…

So much for the science-speak…. What about these copepods on Seychelles whale sharks? Well according to Mark they are easy to collect “just wipe them off with a gloved hand or pull them of with a pair of tweezers….” OK sounds like a great job for Katie! Or not quite… Rather not quite so easily! The first shark we found with copepods seemed completely unfazed about Katie trying to remove them and in fact he seemed to think Katie was a large cleaner fish and appeared to welcome the attention… But come-off the copepods would not and a very miffed Katie returned empty handed.

More extraction power was needed and so on the next trip a pair of surgical forceps were secured ready for use, but as you probably imagined, the sharks on this trip were copepod free! Finally we found a young male shark with both a slightly curled left pectoral fin (photo right), as well as a nice collection of copepods on its top lip.

So Katie went into action again, this time successfully collecting three with the aid of the forceps!

Our first collection of whale shark copepods (Pandarus rhincodonicus); photo and copepods Katie Brooks

So, that’s the first of what we hope will be several copepod collections… We just need to find a bunch more sharks now so Katie can prove she is Queen of the Copepods, or is that shrimps to you and me?

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