Land of the rising hammerheads

David Jacoby

3am, the morning of my flight back to the UK and my throat is hoarse from an evening of karaoke and sake – flight departs in 5 hours!

So ends a truly unforgettable three weeks of work setting up the first shark conservation project in Japanese waters. This highly collaborative project involved a core team of six partners from Miami, Scotland, Hawaii and Tokyo where we all met, along with a reporter and photographer documenting the trip, before we headed south to the oceanic island of Mikomoto, ten kilometres off the coast of the Izu peninsula, Shizuoka Prefecture.

hammerhead sharks

Monitoring shark social interactions

The purpose of our trip was to install acoustic tracking equipment to monitor the space use and social interactions of endangered scalloped hammerhead sharks that periodically visit the waters surrounding this island, occasionally schooling in spectacular numbers. To date, there is no information on this species in the Western Pacific Ocean, yet their proximity to the global shark fin hubs of Hong Kong, China and even local markets at Kesennuma, Japan, make them particularly vulnerable to exploitation.

Tagging in turbulent waters

With the enduring help of Dr Yuuki Watanabe we finally made contact with the dive operators, Mikomoto Hammers, who had made the initial contact with us nearly three years ago. They proved amazingly accommodating and helped us to source a local fishing vessel that had clearly seen some action, from which to carry out our research.

One of several turbulent days at sea.
One of several turbulent days at sea. The skipper did a wonderful job of manoeuvering this very unmanoeuvrable vessel in and around the rocks of the island. Image (c) Tre Packard.

From 7am - 4pm for 10 consecutive days we had people in the water either SCUBA or free diving, surveying suitable locations to moor our receiver equipment or searching and tagging sharks who proved pretty elusive at times.

Due to the rather delicate nature of scalloped hammerhead sharks, we had enlisted the help of professional free diver (and big wave surfer) Mark Healey to help us tag free-ranging sharks with a spear, thus minimising the stress to the animal to a brief spike in the back just behind the first dorsal fin.

Mark Healey surfacing from another 20 m free dive, spear in hand
Mark Healey surfacing from another 20 m free dive, spear in hand. Image (c) Tre Packard.

As an indication of his ability Mark frequently clocked up bottom times of 70 – 90 minutes per day, similar to those of us using SCUBA! In that time, Mikomotojima (island) provided some seriously challenging conditions for us with strong surge and current to throw us around whilst installing our receivers on the seabed and a growing swell at the surface caused by the impending charge of Typhoon Goni swirling up from the central Pacific. Needless to say, we all came out with a newfound respect for the life that resides around Mikomoto in these turbulent waters.

Reaction to video of Mark Healey tagging a hammerhead shark
Reaction of the local dive community to a video of Mark Healey tagging a scalloped hammerhead shark.

A successful trip

We installed six acoustic receivers around the island at depths between 18 – 23m and tagged ten sharks, eight acoustic tags which give off a time-date stamp whenever they are within 250m of our receivers and two satellite tags to record the much broader offshore movements of these animals when they leave the island to feed. 

Acoustic receiver installation
Dr Yannis Papastamatiou and myself installing an acoustic receiver on the seabed. Image (c) Tre Packard.

We are hoping to get more tags out in the future to help inform how important Mikomoto is to the biology of these top predators. Equally importantly, however, this trip enabled us to develop strong relations with the local dive community and fisheries agency who were really enthusiastic about the photos, footage and early outcome of our efforts.

We were all struck by a much greater appreciation for not just the challenges facing marine conservation in Japan but more positively, the strong connection the Japanese have with their surrounding wildlife and the willingness and enthusiasm to understand and be involved in marine conservation issues. 

Find out more about ZSL's scientific research

Scientific research and conservation team
Scientific research and conservation team. Image (c) Tre Packard.



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