Tagging sharks in the Bahamas
To Catch a Tiger
“Tyger, tyger, burning bright / In the forests of the night, / What immortal hand or eye / Could frame thy fearful symmetry?” – William Blake, “The Tyger”
Sharks are hot right now, despite, or perhaps because of, their scarcity. People love them, vilify them, study them or eat their fins. Discovery Channel’s “Shark Week” is one of the year’s most highly anticipated television events, up there with the Super Bowl or finale of “The Bachelor.” Still, they’re very endangered. Some estimates say that 90% of global shark populations have been decimated from the world’s oceans in the past 20 years. This is due to a combination of targeted fishing to satisfy the appetite for shark fin soup, pollution, coral reef degradation or as bycatch in nets and on long lines. This last method, which claimed an estimated 97 million sharks in 2010 alone, accounts for 80% of shark deaths annually and is the subject of an ongoing study being conducted by scientists at the Cape Eleuthera Institute in the Bahamas. We endured a bumpy ride in a tiny turboprop to visit this remote outpost and see what they were finding.
Longline fishing is effective, and brutally so. The process is fairly simple. Fishing boats unspool miles of line with baited hooks hanging at regular intervals. After several hours, the lines are pulled in to see what’s been caught, re-baited and reset. While the goal is to catch big pelagics like tuna, mahi-mahi and cobia, the long line doesn’t discriminate. Drape miles of line of juicy bait in the open ocean and you’re bound to attract attention. Oftentimes that attention includes sharks, drawn by the curiously bobbing free lunch and irresistible smell of bloody fish heads. While shark catches are sometimes considered mere bycatch, collateral damage in the larger quest for other quarry, some are finned for soup, cut up for bait or simply thrown back to the sea, dead or alive. The problem is, sharks take a long time to reach maturity and aren’t prolific reproducers. The oceans are being cleaned out at an alarming rate.
Perhaps fittingly, Eleuthera is shaped like a longline hook, 100 miles long and a mile wide, hanging out over a deep mid-Atlantic abyss. Its barbed southern tip curls around and terminates at Cape Eleuthera, once home to a luxury resort, its abandoned remnants now in overgrown ruins, a reminder of the island’s heady days as a jet set destination. Today, the eerily quiet cape is the site of another sort of utopia: the CEI and its educational facility, The Island School. Founded in the late 1990s by an ex-Navy SEAL, the school draws well-heeled teenagers from all over the world who come to spend a semester learning to dive, conducting research, going on field studies and expeditions and taking academic classes — all while living without Internet and junk food, taking Navy showers and running half marathons. CEI, the research institute, is home base for ecologists and marine biologists, both resident and visiting, studying everything from invasive lionfish and algae to sharks.
The entire scene was chaotic, with the deck listing precariously towards the shark, people shouting and the shark banging against the boat.
The goal of CEI’s Shark Research and Conservation Program’s current project is to study the stress responses of various shark species to longline fishing. These stress responses are measured by drawing and testing blood from hooked sharks and by behavioral observations and detailed charts of their movements while caught. The data collection, as one might expect, involves setting longlines and catching sharks. This is easier said than done, as we saw on our three days on the water with a team of researchers.
To mimic the use of longlines off of fishing boats, the CEI researchers stretch about a hundred yards of line between two anchors with a series of buoys in between. Hanging down from this line are shorter lines with the evil-looking hooks, baited with scraps — lionfish, bonita and mahi-mahi heads. In a bit of innovative jerry-rigging, CEI has devised a way to record activity on the hooks with cameras and even accelerometers, not unlike the one that can tell when you’ve rotated your iPhone. Each hook is suspended below a downward-facing GoPro Hero 3 that records all action, or inaction, on the hook until its battery runs out or its memory card fills up. The accelerometer detects pull on the line and continues to do so as the hook gets pulled hither and yon by a shark, providing precise data that can be graphed and analyzed in minute detail later (a good use of interns). If all of this sounds neat and orderly, the reality is that it was the result of a lot of experimentation, failure, PVC pipe and smelly fish guts.
On our first day out with the crew, we caught a four-foot long reef shark within the first hour, a fortuitous start to our week. If a shark is doing well on the line, Brendan, a lean, twenty-something research assistant, explained, the researchers like to leave it hooked for up to four hours, a better indication of how a longer period of captive time will affect its physiology. I jumped in the water with a snorkel and a camera to take a look. The poor creature made its circuit, at times swimming directly towards me before being yanked back by the hook in its mouth. Some sharks do better on a line than others. Those that can pump water across their gills to breathe can lie motionless for hours without a problem. Others, like this reef shark or the bigger requiem and pelagic sharks, have to swim constantly to breathe and don’t last long on a hook. We wouldn’t make this guy hang out too much longer.
While the GoPro and accelerometer capture movement and visual data, another layer of the story unfolds in the shark’s blood, where elevated levels of glucose, lactate and decreased pH are indications of a shark’s ability, or lack thereof, to cope with the stresses of being hooked on a line for a long period. Getting this blood requires the daunting task of holding the shark still long enough to stick a syringe in it while also measuring its length and fixing a tag to its dorsal fin. When the time came, the team would motor the boat alongside the line, transfer the down line and hook to the bow and grab onto the writhing fish’s tail. This takes a team effort, with one of the interns, Clark, readying the needle, the boat captain keeping the boat nosing into the swells, and Brendan and his research partner, Owen, holding onto the shark and doing the sampling. The blood is tested onboard using the same type of blood glucose meter a diabetic uncle might use, and is then packed away for further analysis back at the lab.
While shark catches are sometimes considered mere bycatch, collateral damage in the larger quest for other quarry, some are finned for soup, cut up for bait or simply thrown back to the sea, dead or alive.
The entire scene is as chaotic as it sounds, with the deck listing precariously towards the shark, people shouting and the shark banging against the boat. Despite the seeming chaos, the CEI team is remarkably efficient, getting what they need and releasing the shark in less than five minutes. Releasing it requires finessing a bolt cutter into the toothy maw to cut off the hook’s barb. Of course, a shark is about as amenable to this crude dental work as your average patient, so it must be flipped onto its back, where it enters a calm state known as tonic immobility. Once the hook is removed, the shark is reoriented and set free, aimed into the depths like an oversized paper airplane.
Science often consists of hours of mind-numbing monotony punctuated by minutes of sheer excitement, and the day after the reef shark excitement was one of those monotonous days. We re-baited the hooks every hour since small fish managed to strip the bait off without getting caught. Clark and Brendan killed time by effortlessly freediving down to 60 feet to observe rays on the bottom; Owen entertained us with his Schwarzenegger impressions. We snorkeled, traded dive stories and donned SCUBA gear to take dramatic photos of the empty hooks bobbing underwater. As the day wore on and the batteries in the GoPro and accelerometers faded, we called it a day. Skunked.
That night, all the talk was of the impending tropical storm bearing down on the Bahamas, and we feared we wouldn’t see another shark before being socked in for the rest of the week. But Tuesday morning dawned bright, with only a stiff breeze and a slight chop from the storm, which had turned north. We motored out to our usual spot and set the lines, Owen optimistically predicting that it was a particularly “sharky” day to our collective skepticism. Hours passed and our hopes faded. That’s when we went to check on that a buoy that was bobbing a little lower than the rest.
“We’ve got a big one, hanging vertically on the line. It’s a tiger. We need to act quickly!” Brendan called out. The crew leaped into action, Clark grabbing the syringes, Owen angling the boat in towards the line, interns scrambling to get test equipment ready. I quickly shouldered my scuba tank, spat in my mask and backrolled into the clear blue Atlantic.
As soon as I hit the water, I spun around to find the shark. There it was, only the boat between us. I could see it writhing against the hull, its telltale stripes and blunt nose confirming its identity: a tiger shark. Tigers are often included in the lists of sharks most dangerous to people. Their size — some grow well over 16 feet — voracious appetites and predilection for swimming in shallower water have set up some unhappy encounters for unlucky swimmers and surfers everywhere from Hawaii to Africa. Most attacks are of the mistaken identity variety, but that’s little consolation when a 1,000-pound shark has removed your leg that he thought was a turtle.
I’d be lying if I said I wasn’t a little scared to be splashing in next to this pissed off predator. I quickly descended below the boat and kept my eyes on the scene above me, which played out in silence other than the rhythmic roar of my own exhaled bubbles. The clear water offered full view of not only the shark but of the crew working on the boat. I could see Owen struggling to secure the flailing tail while Brendan deftly handled the syringe and tag. Then I saw the shark go upside down and the bolt cutters come over the side. It was almost release time.
When the tiger shark was flipped back over, I saw it come to life once again. I considered which way and how quickly it would descend and what he would think of me with my big camera rig. Owen let go of the tail. The big tiger turned and cruised above me without notice, the classic shark shape perfectly silhouetted against the sun. Instead of fear though, I felt a peace as I watched the graceful giant glide away out over the reef wall. I hoped he wouldn’t ever encounter another hook in his life but grow even larger and go on to breed and fill these waters with countless offspring.
We often wonder what science is for; often it seems to exist just for the sake of learning new things, with no immediate purpose. But the shark program at the Cape Eleuthera Institute is literally on the bleeding edge of a global environmental crisis. While they don’t pretend to think the results of their work will end longline commercial fishing, this study provides valuable data to other scientists about how to best conduct their programs. CEI is but one small group conducting one narrowly focused study. Taken together with all the other work scientists are doing elsewhere in the world, the body of knowledge about sharks is growing exponentially. This hard-fought knowledge might end up being what saves the sharks from us. That has teeth.