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Tagging tigers on the line

By Alexandra McInturf, 26th May 2016

In the glowing light of emerging daybreak I could barely see the numbers on my watch: 6.30. The air was chilly and all I could hear was the gentle slapping of water against the hull of the boat. The bow turned towards the Tiger Grounds, we picked up speed and I curled up contentedly in my foul-weather gear. This was my first long-line experience and I was excited to see exactly how the process worked.

I’ve never had an extensive knowledge of fishing methods. Before I arrived at the Shark Lab in Bimini in January 2016, the term ‘long-line’ conjured dark images of the floating corpses of by-catch: turtles, dolphins and, of course, my beloved sharks. I won’t argue that there isn’t some truth to this connotation. In fact, long-lining is prohibited even here in Bahamian waters without a special permit. However, within my first few days at the Shark Lab I was introduced to doctoral candidate Matthew Smukall, whose project on the ecology of tiger sharks relies heavily on long-lining as a method of capture. Matt explained that with the proper precautions in place, checks every four hours and careful monitoring of the shark throughout the analysis procedure, this potential death-trap could become a valuable research tool. The results of this project contribute to greater understanding of effective shark management on a local and global scale.

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Clipping float. Photo © Charlotte Sams

As the sun rose we formed a well-practised assembly line. In the water went the first anchor and cinder block, marking our starting point. Then we began. ‘Float!’ ‘Gangion!’ The commands rang clear and were quickly obeyed. The corresponding piece of equipment was attached via tuna clip and the line was thrown over the side of the boat, slowly creating a long tail of bouncing white floats behind us. After 15 repetitions for each line, we set a second cinder block and anchor, tightening the entire line against the seabed only a few metres below. The gangions dangled tantalisingly in the water, barracuda bait visible in the turquoise blue.

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Floats. Photo © Charlotte Sams.

We had just heaved the last cinder block overboard when we heard a splash. ‘Look over there! There’s something in the water!’ Indeed, as we all craned our necks, we could see the very white underside of a very large shark tail thrashing out of the water only a few hundred metres behind us. As if to defy completely our expectations of gravity and normal shark behaviour, the tail remained in the air for several slow seconds. ‘Is it on our bait?’ someone finally had the courage to ask. Rather than jinx the capture of a potential leviathan, we remained silent as the boat turned around.

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Checking lines. Photo © Ben Leeson

It’s difficult to explain one’s reaction to a 3.7-metre tiger shark. I felt some combination of awe, reverence and, naturally, a healthy dose of fear. Judging by the exclamations of the veteran researchers around me, I wasn’t alone. Within an hour of the initial sighting, we could see the famed Dr ‘Doc’ Gruber at the helm of a second boat, accompanied by more of the Shark Lab staff. Though this species is known for its durability, the team wasted no time conducting a work-up. I had seen a work-up previously on a few occasions. Here they are typical procedure and an important form of collecting data. However, obtaining length and girth measurements, injecting NMFS Casey and PIT tags to mark the individual for future identification, taking blood, DNA and isotope samples, and surgically embedding an acoustic receiver under the skin of an animal easily heavier than 500 pounds (225 kilograms) requires strength and experience that few possess. The shark swam off slowly, seemingly unfazed, and there were high-fives all round. I later learn that this was one of the largest sharks the lab had ever seen.

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Photo © Ben Leeson

In retrospect, it’s incredible to me that a shark this size could roam into such clear, shallow water without attracting human notice. How frequently this might occur, I cannot begin to guess, although I’m sure Matt’s project will provide more insight over the next few years. Even so, in a world shrunken by the technologies of the digital age, our oceans are still a mystery.

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Tiger shark on the line. Photo © Charlotte Sams

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