A while ago, Robin Nagy sent me an excellent set of underwater photographs shot at Chumphon Pinnacle in the Gulf of Thailand. Chumphon Pinnacle is a popular dive location offering excellent diving conditions that attract thousands of diver each year. Shark sightings at the site have consistently been reported as grey reef sharks (Carcharhinus amblyrhynchos) by local dive guides and professionals. But sharks encountered at Chumphon Pinnacle were misidentified in the past and are in fact bull sharks! The short, bluntly rounded snout and the large and broadly triangular first dorsal fin originating over or just behind pectoral insertion rules out these specimens to be grey reef sharks.
Bull sharks are widespread along the continental coasts of all tropical and subtropical seas but also occur around remote island states far away from continental waters. Although sharks of the genus Carcharhinus are rather uniform and can be difficult to distinguish from one another in the field, the diagnostic features of this heavy-bodied species make it readily distinguishable from other species.
Despite common species misidentification, it has long been recognised that direct observations by divers can yield valuable information on the behaviour and ecology of fish. Because underwater observations are made in the natural environment of the animal often without any manipulation, behavioural observations are mainly anecdotal in nature. Nevertheless, the results can provide excellent preliminary data that benefit from follow-up studies using other methods or provide researchers with rare opportunities to witness complete and natural acts of the secret life of fish.
Only a few sites are known where free-ranging bull sharks are accessible for direct underwater observations. The identification of Chumphon Pinnacle as an encounter site for free-ranging bull sharks offers the possibility to set up an observation programme in the Gulf of Thailand that eventually adds to the knowledge about the behaviour and ecology of this little known apex predator.
Let me know when you go there!