Thursday, February 23, 2006

Monochrome reef sharks

Blacktip and Whitetip reef sharks are probably two of the sharks most commonly seen by divers in the Indo-pacific region. As the pictures below show you don't need to be a rocket scientist to understand how they get their names, just check out their dorsal fins (the jaws-looking one on their backs). Whitetips (Triaenodon obesus) are nocturnal predators and tend to be seen sat lounging about on the sand or in caves waiting for night to fall. Unlike many sharks they can pump water over their gill so don't need to swim all the time.

Blacktip reefies (Carcharhinus melanopterus) by contrast do and are often seen crusing sand flats. The juveniles sometimes swim in knee deep water and I've often been paddling with them swimming around my feet. This was one of a group of five individuals on a beach in Pulau Lang Tengah, Malaysia.

and here are four of the five schooling together. Juvenile Blacktip reef sharks have been observed hunting cooperatively on schools of small fish.

In spite of what I said earlier about their common names making perfect sense once other species are thrown into the mix things get a little confusing: C. longimanus (the oceanic whitetip) and C. albimarginatus (the silvertip) both have white fin tips as does a regional variant of C. amblyrhynchos (the grey reef shark) meanwhile there are two other "blacktips" C. limbatus and C. tilsonii). Confused yet?

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