How researchers are tracking great white sharks

20 Dec 2013

Mary Lee aboard the M/V Ocearch


Greg Skomal clambered onto the hydraulic lift of a modified 126-foot Bering Sea crab fishing boat off of Cape Cod, staring at the object of his life's devotion: 3,500 pounds of writhing, gunmetal gray muscle, shimmering under the ship's spotlights.

Skomal and the crew of the M/V Ocearch covered the shark's face with a towel, stuck a hose in its mouth to irrigate its gills and began attending the great white with the speed of a Formula 1 pit crew.

The starstruck researchers took blood samples, checked the shark for parasites, implanted an acoustic pinger in its gut, and even performed an ultrasound -- all within 15 minutes and without tranquilisers or anesthetics. The crown jewel of the operation, though, was a state-of-the-art satellite transmitter, drilled and bolted onto the shark's dorsal fin.

Exhausted and newly rigged with an arsenal of technology, the shark -- christened Mary Lee -- slid into the water and swam languidly out of sight.

Skomal has spent decades on Martha's Vineyard and Cape Cod as the state's top shark scientist for the Division of Marine Fisheries. He's researched these animals for decades, but this was unlike anything he'd done before. "What really surprises you the most is the sheer size and mass of this animal out of the water," he said. "It's an absolutely amazing and humbling experience."

Earlier this month, a little over a year after capturing Mary Lee, Skomal stood in the office of his colleague, Simon Thorrold, a senior scientist at the Woods Hole Oceanographic Institution.

Thorrold pulled up the data that Mary Lee has been pinging back for the past year.

The display revealed a true ocean wanderer. Her track resembled a drunkard's walk around the entire North Atlantic. After her capture off of Cape Cod, Mary Lee's pings led the researchers to Jacksonville in March where Ocearch, a research nonprofit, caught and tagged another mature female, Lydia, plying the murky, dolphin-stocked waters at the mouth of the St. John's River.

The data transmitted from these two sharks in the past year has been a revelation. Skomal and Thorrold are looking for patterns that might reveal something about the animals' lifestyle.

It has been nearly four decades since a creaky animatronic shark terrorised movie audiences and Amity Island in Jaws, but the lives of the Atlantic great whites still remain, for the most part, a mystery.

The researchers are searching for recurring tracks and well-trod patches of ocean that might illuminate important nurseries, breeding or feeding grounds, information that could lead to eventual conservation measures. But so far the data has been frustratingly -- even thrillingly -- erratic. "There's no frickin' pattern at all," Skomal said.

Strange behaviour

Conventional wisdom held that the sharks would hunt seals off of Cape Cod in the summer and then head to Florida in the winter. "We expected them to do the snowbird thing," said Thorrold. Well, it's December and Mary Lee has, in fact, returned to Florida, but Lydia isn't following that script. Her most recent flurry of pings has come from just off of Newfoundland, 1,000 miles away, in water just a few degrees above freezing. "What on earth is she doing there?" Thorrold said, laughing at the strangeness of it.

The wandering paths of Mary Lee (red) and Lydia (yellow) since their release

Ocearch Global Shark Tracker

Rather than orderly seasonal migrations, the two sharks have rocketed up and down the coast several times, traveling thousands of miles in only a few months, canyoneering and scaling underwater mountains and spending months well off the continental shelf in the middle of the North Atlantic, only to return to the coast by swimming under the Gulf stream.

Meanwhile in South Carolina, residents were alarmed to find half-eaten dolphins wash ashore suspiciously close to Mary Lee's arrival in the area (Skomal says it probably was a shark that tore the dolphins apart, though a number of species could be responsible, and it's unclear whether it was a case of active predation or carcass scavenging).

While the Smart Position and Temperature, or SPOT tags anchored in the sharks' dorsal fins, have revealed their horizontal movements, Ocearch attached an additional tag, known as a Pop-up Satellite Archival Tag, or PSAT, to Lydia to record diving depths and water temperature. Skomal has tagged other sharks in the Atlantic with PSATs but Lydia, it appears, is something of a performer. "Did you say you have her diving down to 1,000 meters?" he asked rubbing his forehead as Thorrold pulled up data profiling the shark's diving behaviour. Indeed, Lydia has been fond of plunging into the darkness off the continental shelf several times a day, maxing out at 3,543 feet.

What she's doing at these incredible depths is unknown, though she may be feeding in the so-called "deep scattering layer," a dense seam of fish and squid discovered by military sonar during World War II. The layer rises hundreds of meters during the night and falls back down during the day, staying in perpetual darkness.

While the open oceans have been traditionally considered a desert for life, Thorrold thinks that this sentiment is more a reflection of human ignorance. "There's got to be a lot more than we think down there," he said, hammering the point home with the dietary requirements of another marine species that exploits the deep scattering layer. As a species, sperm whales take nearly as much food from the ocean each year as humans do, he says.

While Lydia and Mary Lee have been great subjects, three other Atlantic whites tagged by Ocearch have been less cooperative. Their satellite tags hardly ever ping back their coordinates. The transmitters can only communicate with satellites when the sharks are at the surface, and it's possible these three are sticking close to the coast, where relatively warm waters could enable them to stay under for long periods of time. (Ocearch has tagged a total of nearly 50 sharks, including some mako and bull sharks, but these five whites are the only ones tagged so far in the Atlantic).

East vs. west

Ocearch is not the first group to tag and track great whites. On the West Coast, researchers led by Barbara Block of Stanford have tagged more than 200 great white sharks over more than a decade with PSATs, as well as acoustic tags whose pings are picked up by hundreds of receivers along the coast.

These studies have revealed regular migration patterns, as well as a number of hotspots where the sharks regularly congregate, such as the waters off the Farallon Islands, Año Nuevo and Point Reyes, where Monterey Bay Aquarium research scientist Sal Jorgensen tagged four sharks earlier this month. Jorgensen has been working with Block for the past eight years tagging and photo IDing sharks and analysing the data.


It turns out mature females enjoy an occasional jaunt to Hawaii while baby sharks, wary of being cannibalised by the adults, are content to hide out off Manhattan Beach in Los Angeles.

But even the more predictable Pacific great whites still mystify the scientists who know them best. Most peculiar is the midwinter migration between central California to the so-called White Shark Café, a giant patch of ocean between Hawaii and Baja California where the animals gather every year. "Why are all these sharks going out to this area that has been historically considered the desert of the Pacific Ocean?" he asked. "It's almost like Burning Man."

One clue could be found in the same kind of PSAT data that is revealing the diving habits of Lydia an ocean away. Block's team has found that when the males are in the Café they practice two types of dives: deep diving (likely for food) and a mysterious and energy-intensive type of dive characterised by rapid bursts up and down the water column. "The sharks are moving between 50 meters and 250 meters very fast up and down, up and down, all day and all night -- sometimes over 100 times a day, swimming faster than their terminal velocity in water," Jorgensen says.

He thinks they're looking for mates. Many species of sharks emit pheromones to signal their readiness to mate. The water the sharks are swimming in is characterised by layers separated by temperature, and any pheromones would spread out horizontally along these layers. Jorgensen posits that the hot-and-bothered males at the White Shark Café are frantically inventorying these layers for wafts of lady chemicals that would lead them to the source.


Ocearch founder Chris Fischer, former host of the TV series Offshore Adventures and a marine conservation advocate, has tagged sharks in Guadalupe Island off of Mexico. He isn't so sure that the sharks are mating in the White Shark Café. "They think that the sharks gather at the Farallons but they're not breeding, then they wander out into the middle of the ocean and spread out into an area the size of Alaska and breed out there?" he says. "That makes no sense."

To Fischer, the situation underscores how much remains to be learned even about this well-monitored Pacific population.

He says he has approached West Coast scientists about tagging the sharks and been rebuffed, a topic that still provokes some soreness ("Those guys hate me," he says).

When asked about Ocearch, Jorgensen is more diplomatic, saying simply that with dozens of tagged sharks already in the water, and with the acoustic tags returning up to four years of data on individual sharks, the group has all the data it needs.

Fischer sees the West Coast researchers as uncooperative and rooted in traditional academia, where scientists typically keep their data close until they're ready to publish it. He's committed Ocearch to making all of its data available to the public in real time. (The West Coast researchers have made efforts to do this too -- last summer releasing a smartphone app called Shark Net that allows the public to keep tabs on the acoustic pings of their sharks in real time).

The biggest difference, though, lies in the tagging strategies of the two teams. The SPOT tags used by Ocearch had previously been used only on smaller animals like seals and turtles, and the tags do have some clear advantages over the use of PSATs alone.

The biggest advantage is real-time data -- PSATs pop off the sharks after months of data collection and float to the surface (most of the time) before transmitting all at once to a satellite -- and location accuracy. PSATs rely on techniques honed by ancient mariners to determine their location, measuring daylight and water temperatures to estimate latitude and longitude. As a result they can be off by hundreds of miles. SPOT tags, in contrast, rely on GPS. "Our dots are much more accurate than theirs," Skomal said.

The most striking difference though may be the method by which the two tags are attached to the shark. PSAT tags are generally attached by dart-tipped harpoons rather than the dramatic on-board surgery of Ocearch, which has drawn criticism from some animal welfare advocates who claim the procedure traumatises the animals, which are listed as a vulnerable species by the International Union for Conservation of Nature. A small but vocal group of critics started a Facebook page to chronicle what they see as the group's abuses, and in one case detractors circulated a petition in an unsuccessful attempt to prevent Ocearch from getting a permit for an expedition in Massachusetts.

Fischer, who's not a scientist but has been tagging sharks since 2007, dismisses the criticism, noting that sharks regularly engage in far more harmful activity amongst themselves. "These animals lead very violent lives," he says. "They bite each other in the head when they have sex. They bite each other's fins off. They have an amazing capacity to heal."

Sea change

If the Pacific sharks are better understood, it's partly because tagging sharks in the Atlantic has only become possible in the past few years. That is thanks to the emergence of a single hotspot, the first of its kind on the East Coast: Chatham, Massachusetts on Cape Cod. "When you're spending the kind of money we are to move a ship around the world, you're looking for what we call 'predictable access' to the animals," says Fischer. "That has become the first place where we have predictable access. It's the best spot in the Atlantic."

The reason the sharks have just begun to reliably appear on the Cape every summer is visible from Google Earth. Type Monomoy Island into the search bar, peruse the shores for a few moments and odd blotches composed of thousands of black flecks appear. These are the colonies of grey seals, which had been hunted to virtual extinction in the region until the passage of the Marine Mammal Protection Act in 1972.

For decades theirs was a slow and steady recovery as a remnant population in Canada recolonized New England. In the past few years though, the population has hit a threshold and exploded. For the whites, who may live upwards of a century, the boom has meant a return to ancestral hunting grounds. In 2013 Massachusetts witnessed its first shark attack since 1936.

But the return of the great whites might actually reflect a real increase in their own population as well.

Sharks were decimated by the Atlantic swordfish longline fleet in the 1980s and 1990s (longlines are fishing lines 20 to 40 miles long that are baited with thousands of hooks and catch everything from seabirds to sea turtles). As swordfish were severely overfished in the North Atlantic, regulators have drastically cut the fleet over the past two decades, from 300 in 1995 to fewer than 100 active boats today.

The unintended consequence has been catching fewer great whites as well. The sharks still face threats from the gillnet fisheries, particularly the monkfish fishery, but a 2011 endangered species listing for Atlantic sturgeon may soon rein in that industry as well (gillnets are gigantic walls of mesh that are left stationary in the ocean that target fish but also entangle larger animals like dolphins and turtles).

Great whites also gained a measure of federal protection in 1997 when fisheries regulators outlawed their intentional capture, putting an end to the Jaws-inspired great white hunts that would regularly launch from Montauk in the late 1970s and 1980s.

All this is good news for Atlantic sharks -- and those who would track them.

Vicious but vulnerable

More than any other animal, sharks are responsible for the foreboding sense that, as David Foster Wallace put it, the ocean is a "primordial nada . . . inhabited by tooth-studded things rising angelically toward you."

To landlubbers, sharks can seem mindless, indifferent to suffering and fundamentally unlovable, with a gaze as blank and pitiless as the sun. Highlight reels of vicious attacks proliferating across cable TV do little to underscore their vulnerability and need for protection.

Sharks have been swimming the oceans for almost a half-billion years -- they have been around longer than trees -- yet their biggest threat comes from a single dish: shark fin soup. Every year millions of sharks are captured at sea, often finned and then discarded alive to fuel the market for the soup, a status symbol among China's growing middle class.

Unlike many fish, sharks mature late and have few offspring, making them particularly vulnerable to overfishing.

Thorrold is worried that the oceans are being emptied of their apex predators just as scientists are beginning to understand the role they play in the ecosystem. On pristine reefs, untouched by human interference, sharks can account for almost three-quarters of the biomass. "When you think about that, it's absolutely crazy," he says. "How is that even possible? It's like going to the Serengeti and seeing thousands of lions and a few wildebeests. It just doesn't make any sense. I think what it means is that we don't understand how ocean ecosystems and food webs actually work."

With each passing day though, they are learning more.

Hundreds of miles away, Lydia and Mary Lee were still pinging day and night, near the shore, off the shelf, basking in the sun, plunging into the cold, dark deep and all the while baffling the scientists. "Nothing surprises us anymore," says Skomal. "The more of these tags we put out, the more we realise these fish do things that we could never anticipate."

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