We recently came across this article written by Tristan Guttridge at the Bimini Biological Field Station explaining how some of the tagging takes place with the Great Hammerheads in Bimini, Bahamas. Bimini is undoubtedly the best place to encounter the Great Hammerhead Sharks and has seen a recent boom in dive related tourism. Here’s Tristan’s explanation of the tagging process:

In short, by using a basic float-fishing technique taught to us by an ex-commercial shark fisherman in Florida. After mastering this method, with his guidance, we are now able to capture, tag and safely release a great hammerhead shark in less than 15 minutes. This is how we do it:

0 minutes: Once hooked, the hammerhead typically swims away, diving into deeper water (where available) and towing our set-up of giant buoys. The shark’s powerful turns and deep dives cause the buoys to submerge under the waves.

3 minutes: We intuitively ‘feel’ the shark moving through the water column and give it more line to manoeuvre and even dive if it wants to. Then we slowly and carefully haul in the line and after a few minutes the sensitive hammerhead reaches our boat, not in a state of exhaustion.

6 minutes: Once it is alongside our vessel, we point the shark into the current to ensure that water is flowing through its gills and supplying maximum oxygenation. One member of the team then holds the hammerhead’s dorsal fin to provide stability while others gently secure its tail and pectoral fins with ropes.

10 minutes: Another team member gently but firmly holds the shark’s head to prevent eye damage and to help turn the shark slowly over into tonic immobility so that it is calm and ready for a research ‘work-up’. Length measurements (nose to fork) are quickly taken and a 10-year acoustic tracking device is surgically implanted. Two small fin clips are then taken for DNA and stable isotope (diet) analysis.

13 minutes: On completion of the work-up, the shark is turned right side up, a miniature microchip PIT tag is inserted for long-term identification and an external tag (NMFS; National Marine Fishery Service) is placed on the shark for visual observations.

15 minutes: Finally, the hook is removed and the shark is released with strong push to set it on its way.

For example, of the great hammerheads caught in commercial, bottom-longline fisheries in the north-western Atlantic and Gulf of Mexico between 1994 and 2005, 90% were dead by the time they were brought alongside the fishing vessel. This vulnerability makes hammerheads as a group very difficult to work with and they are therefore poorly studied.

For the full article and more photos, read Hammerhead pitstop « Save Our Seas Foundation