This sort of information is so valuable in part because it gives scientists a sense of what parts of the ocean need to be sheltered more than others. Faced with the enormity of the sea, and the many different demands on it, conservationists are trying to identify the most ecologically valuable regions so they can establish marine protected areas. That way they can strike a deal with competing groups such as commercial and recreational fishing interests: leave these parts of the ocean alone, and you can exploit the rest.
Pikitch and her top assistants, Demian Chapman and Elizabeth Babcock, have been tracking their sharks with fairly straightforward, inexpensive monitoring equipment, spaghetti tags and radio transmitters, both of which can be applied to a shark once it’s lassoed. The spaghetti tags help researchers identify individual animals once they’re recaught, while the acoustic tags send radio signals that provide scientists with a sense of where a shark has traveled over time.
Once I’ve conducted the lasso operation with Chapman’s assistance, the scientists first record some basic information about the shark we’ve secured to the side of the boat. Using a simple band of measuring tape, they record the shark’s species and gender along with three separate lengths for the shark, because different researchers rely on different measurements. The first measurement captures the distance between a shark’s snout and the upper part of its tail, the second goes from the snout to the fork in its tail, and the third reaches from the snout to the tail’s end. Then it’s time for a quick surgical operation.
While keeping the shark secured in the water, Chapman makes a surgical incision about an inch long, right next to the dorsal fin. This allows him to insert an acoustic tag that will send a unique signal every time the shark swims within 1,640 feet of the nearly two dozen radio transmitters the team has stationed throughout the reef. With a few swift motions Chapman stitches up the incision, and we prepare to release the shark, taking care to make sure it doesn’t savage us in the process. I loosen the noose, he clips the hook with a pair of pliers, and I yank the rope back, sliding it easily over the shark’s tail. Then it’s off, thrashing furiously as it leaves behind the researchers who detained it from its usual cruising activity.
One of the oddest aspects of surveying sharks is that, in the end, it’s still fishing: you never know what you’ll wind up getting. In order to get a sizable variety of sharks, Pikitch and her team fish at night as well as during the day, since different species are active at particular times of day.
Because Glover’s Reef is full of shallow patch reefs, negotiating the waters at night without wrecking the boat amounts to a feat in itself. Only one man seems equipped to do this: Norlan Lamb, a Belizean fisherman who has worked on Pikitch’s project for nearly a decade. While Lamb uses GPS maps to get a general idea of how to negotiate the reefs, he relies mainly on instinct to avoid a shipwreck. He sometimes wears his sunglasses at night—it’s sort of a Zen approach, from what I could glean from our conversations.
Once Lamb has zipped across the reef to the study site, the researchers begin to check the line they set earlier in the day for sharks. The first shark that appears is a pregnant sharpnose: when it makes it onto the deck, its babies are squirming visibly inside, their small bodies forming clear and shifting outlines on her stomach’s surface. The shark’s eyes sparkle in the reflection of the assorted headlamps pointed in her direction; after Chapman and Babcock place a simple spaghetti tag on her, they let her go. Then they turn their attention to two male Caribbean reef sharks caught on the line; since both of them have been tagged in the past, they just jot down the tag numbers and identifying characteristics before releasing them. Still, even this basic summary requires the whole lasso routine, which at times doesn’t go so smoothly.
Once the scientists manage to tag their random collection of sharks, it’s up to the fish to let them know what’s happening underwater. The twenty-two monitors sit at the bottom of the sea for six months at a time, and before long these relays begin to blend into their surroundings in the way that a shipwreck does. The team refers to one of its relays as a “lobster farm” because, in Chapman’s words, “it’s got little wee lobsters all over it.” Another is so covered with algae it looks more like the outcropping of a reef than a piece of electronic equipment. But how they look is, ultimately, irrelevant. All the researchers care about is what signals they receive and transmit back to the research station.
After a decade of surveying Glover’s Reef and acoustically tagging more than fifty sharks, Pikitch and her colleagues can draw some basic conclusions. The sharks they find here stay in the atoll year-round: unlike some pelagic species, which roam far and wide, these animals display a remarkable fidelity to these waters. But they defy expectations in some respects. As Chapman observes, “These sharks are thought of generally as shallow, coral reef sharks.” But the acoustic tags testify to something different. One of the sharks they tracked dived down twelve hundred feet into water that was just thirty-nine degrees Fahrenheit. “You throw some technology at it, and find they live way down deep,” he says, adding that technology has “almost completely rewritten our understanding of their life history and biology. If you read shark books from a decade ago, large tracts of them are incorrect.”
Researchers used to think great white sharks were largely coastal dwellers; now they know these creatures are pelagic as well, capable of crossing vast stretches of ocean. They had believed sharks of all species could conceive only through copulation; Chapman has proved them wrong. And now that scientists are capable of attaching sensors to sharks that track their dives below the surface, researchers are beginning to understand how low the sharks go. A decade ago conventional wisdom held that Caribbean reef sharks live almost exclusively up on top of the reef, but tagging now proves they regularly dive anywhere from four hundred to a thousand feet below the surface.
The sharks in Bimini confounded the scientists’ expectations in a number of ways: nurse sharks have the reputation of being “couch potatoes,” in Pikitch’s words—they’re the sharks you’re most apt to run into if you’re snorkeling in a reef, since they often just rest at the ocean’s bottom—but according to radio tracking they’re fairly active. In July 2004 the team tagged a young female they describe as “Nurse Shark 3333”: this shark circumnavigated the entire reef, which spans 116 square miles, several times within a 150-day period. Caribbean Shark 3348, an adult male tagged in May 2004, proved to be a little more adventurous. At times during his 150-day tracking period this shark left Glover’s Reef entirely: at one point he swam nearly nineteen miles to Lighthouse Reef, where a separate set of researchers picked up his acoustic signal on their equipment. These results suggest that if Belizean authorities established stringent marine reserves in Glover’s Reef that were off-limits to fishing, they would protect the sharks from harm, since the fish tend to remain in the same general area. More broadly, now that it’s clear some pelagic sharks can cross ocean basins, international policy makers need to start thinking of ways to regulate fishing activities on the high seas.
Glover’s Reef, one of just four coral atolls in the Western Hemisphere, already enjoys some shelter from exploitation as a UNESCO World Heritage site. At the moment 30 percent of the reef experiences no fishing at all, and authorities prohibit gillnetting and long-lining—the more damaging fishing techniques—throughout the rest of the reef. Gill nets—massive mesh operations anchored by a lead line below and a float line on the sea’s surface—catch anything and everything that swims into their path, earning them the nickname “wall of death.” As a way of making peace with local fishing interests, the researchers have worked to construct a sort of shark park: part of it is off-limits to fishing, while a “general use zone” allows only artisanal fisheries, which generally inflict less damage than large, industrial-scale fishing operations. When local authorities initially set the rules, they were more focused on banning industrialized fleets than protecting Pikitch’s study subjects. “It just happens it’s worked bloody well fo
r sharks,” Chapman observes. But the scientists are now pushing for even more restrictions, and local government officials have indicated they’re willing to expand upon the current regime. In 2007, the local fishery management council proposed banning shark fishing entirely in Glover’s Reef. Rachel Graham, a Wildlife Conservation Society scientist who lives full-time in Belize and has surveyed a broader range of sharks there, has spent years working with authorities there in an effort to ban shark finning nationwide.
“They still have a chance here in Belize,” Pikitch insists, even though she knows there’s a limited amount of time for activists to protect the reef. The top predatory shark populations within Glover’s Reef have remained stable between 2000 and 2007, according to her survey, which is no small achievement given the rise in shark catches elsewhere in Belize. But other reefs don’t enjoy the same level of protection, and they’re the ones that are coming under increasingly intense fishing pressure.
When Pikitch first came to the country in the mid-1990s, she rarely saw sharks at the market, which she regularly visits to buy bait. Belizeans don’t particularly crave shark: the fish only started showing up for sale once the shark fin market began to boom in the late 1990s. In 2005, Pikitch was concerned to learn that a nurse shark—which has relatively small fins, and therefore fetches just a modest price—was for sale at the market. As the demand for fins has risen, fishermen are going to any lengths possible to bring sharks to market to take advantage of the high prices before they disappear.
“I just gasped, because that is really scary,” she says, as we prepare to head out on our fish shopping trip in Belize City. “The sharks are starting to go.”
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While Pikitch and her team can handle most of the sharks in Glover’s Reef with relative ease, not all sharks can be monitored by swinging a lasso around them and surgically implanting an acoustic tag. Given that whale sharks are roughly the same size as a school bus, it’s not easy to haul one of those fish over the side of their boat and cut it open. This is where the slingshot comes in.
One of the best places in the world to spot whale sharks is off Isla Holbox, site of a former pirates’ cove off the Yucatán, lying roughly ninety miles northwest of Cancún. At this point Isla Holbox, a sleepy tourist town whose only motorized vehicles are golf carts, has become a critical research location where American and Mexican scientists are seeking to determine the migration patterns of sharks that cross national borders regularly as they traverse the Mesoamerican reef.
Robert Hueter, from Mote Marine Laboratory, spotted his first whale shark in 1975, when he was a graduate student at the University of Miami and a whale shark managed to make its way up Florida Bay. The whale shark eventually disappeared, and a week later it was found dead. Hueter didn’t spot another for a quarter century.
He started coming down to Isla Holbox back in 1994. At the time, he was researching blacktip sharks, which gave birth in one of the island’s secluded lagoons. After nearly a decade some of the locals informed Hueter that in late May and early June—just after he would leave town to return to Florida—a posse of whale sharks would come into the region. Curious, he helped convene a group of fishermen, activists, and Mexican and American scientists to determine what was happening.
Like Pikitch, the survey Mote scientists have constructed with researchers from Proyecto Dominó, a Mexican-based conservation group, seeks what amounts to bare-bones information about the sharks that arrive at the start of each summer and depart by the time fall arrives. What does this animal population look like, why do they come here, and where do they go when they leave? Rafael de la Parra, who heads Proyecto Dominó (the locals coined the nickname dominó for whale sharks because of their many spots), says he and his colleagues can’t expect to protect the sharks if they don’t have a clue about how they operate. While shark researchers are using some of the most sophisticated scientific techniques that now exist for tracking their subjects’ movements, they are starting from a base of knowledge that lags decades behind their terrestrial counterparts. All that, and in order to get any work done, they have to aim a fancy slingshot at a beast that could easily crush them.
At first glance, Rafael de la Parra doesn’t look like much of a spear carrier. De la Parra—who generally goes by Rafi—is a somewhat portly, middle-aged Mexican in a black Speedo and snorkeling mask, holding a tagging spear. He boasts a beatific smile nearly all the time, except when a given tour operator pisses him off. Then he glowers.
But right now he is smiling, because we have spotted a congregation of whale sharks, and he’s ready to dive in. He has a clear goal in mind: jump in the water and deploy the elastic band on his metal pole as soon as he gets within striking distance of the shark, which is about three feet away. At that moment, once he’s angled it properly, he releases the elastic with his thumb so that the tag will shoot forward and attach itself to the side just below the fish’s front dorsal fin. De la Parra can accomplish this feat in a matter of seconds, with the ease of an expert javelin thrower.
With little warning, de la Parra slips off the boat and heads toward the massive polka-dotted animal that’s swimming alongside our vessel. I scramble in after him and manage to get close enough to see him fire the tag into the shark’s body. De la Parra is within reach to determine the fish’s sex: as he pops up on the surface, he shouts, “Macho!” before submerging once again.
De la Parra has done this dozens of times: at this point researchers have tagged more than seven hundred whale sharks in the region since they started studying them in earnest in 2003. In fact, tagging whale sharks is the least difficult part of their job: Hueter, who has personally tagged at least three thousand sharks over the past thirty years, says whale sharks are easy targets. “In a thirty-foot long shark, they don’t even flinch.” But once they’ve gotten an animal tagged—especially if they’re using a satellite or acoustic tag—the challenge begins.
On this particular afternoon, for example, I’ve joined de la Parra, Hueter, and another Mote senior biologist, John Tyminski, as they track the path of the shark to which de la Parra has affixed an acoustic tag. Standing by the tracking equipment, Tyminski recaps what we’ve done today when it comes to placing the tag on the shark. “At 13:20, we put it in a mature male seven miles north of Cabo Catoche, ten nautical miles north of Cabo Catoche point.” The biologist can also record water the shark started cruising in once it was tagged—it’s 78.96 degrees Fahrenheit, composed of 14.4 percent dissolved oxygen. But where’s the shark now?
Nowhere to be found. Apparently, something has gone wrong. We circle the water in broad loops for hours, hoping to pick up a signal from the tag, which conveys a high-frequency beep every second to a hydrophone the scientists are monitoring on the boat. If the animal is within thirty-seven miles of the tracking equipment, the researchers should be able to use the hydrophone to determine which direction the sound is coming from, and thereby keep track of the shark. But in this case, either the shark is an extremely fast swimmer or the equipment—a $650 acoustic tag with a depth sensor—has failed. We are practically, as Hueter explains, “looking for a needle in a haystack.”
“Active tracking has never been one of my favorite things to do,” he says, as the afternoon wears on and the sun continues to beat down on us. “Even when it works, it’s very tedious.” And, in this case, it’s not working.
This is the fundamental problem with shark tracking: it’s costly, complicated, and unreliable, even though it’s essential to understanding these ocean predators. Rachel Graham of the Wildlife Conservation Society uses three different methods to monitor the whale sharks she tracks: photo identification (each whale shark has a unique spotted pattern), satellite tags, and acoustic tags. Back in 2000, Graham placed the first pop-up satellite archival tag on a whale shark. These instruments contain a miniature computer that measures pressure, light, and temperature. This combination of measurements gives scientists a precise sense of where the sharks are traveling, in terms of not
just latitude and longitude but also depth. Researchers like Graham program the tags for a set period of time, and when they pop off the animal, they transmit streaming bytes of data to an earth-orbiting satellite, providing a snapshot of what the shark was doing at a given point in time.
These tags can provide a treasure trove of information. Once Graham, diving with her husband, Dan, spotted an archival tag she needed to recover. “Get that tag!” she screamed. (They were underwater, but he got the point.) The tag offered up 206 days of information on what a whale shark had been doing—including diving to unprecedented depths of nearly five thousand feet.
And while Hueter and his colleagues have lost tags on many occasions, the ones that have stayed on have provided promising clues to where whale sharks travel when no one can see them. For years, scientists have suspected the animals give birth in remote areas of the ocean, because no one has spotted their young off the Atlantic coast. In 2007 his team attached a satellite tag to a twenty-five-foot-long female with a rotund belly they nicknamed Rio Lady. Over the following 150-day period, the whale shark traveled nearly five thousand miles from the Yucatán Peninsula through the Caribbean Sea to south of the equator between Brazil and Africa. The area where she ended up, north of Ascension Island and south of St. Peter and St. Paul Rocks, is remote but full of marine life, including sea turtles, billfish, and other sharks. Hueter believes he’s found one of the whale sharks’ elusive pupping grounds, though it will take more research to verify whether that’s true.
Whether it’s satellite and radio tagging or genetic sampling, shark tracking has produced several of the most significant advances in how we understand sharks’ movements and their evolution. It is how we have come to know that great white sharks off the coast of California hover much closer to us than we previously thought.
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