Stranger Than Fiction
- Doug Perrine
- Aug 01, 2009
From the cold, dark waters of the St. Lawrence River comes a creature with antifreeze in its flesh, meat toxic to humans and a body mass rivaling that of the great white shark
IT’S THE DRAMATIC PEAK of many films—that gut-wrenching moment when the hunter fears he has become the hunted. It happened to Canadian divers Jeffrey Gallant and Chris Harvey-Clark when a massive dark shape passed right in front of them shortly after they landed in pea-soup conditions on the bottom of the St. Lawrence Estuary.
Gallant is a shark researcher and author who began diving at the age of 14 and has even lived underwater as an aquanaut, but none of his previous experience had prepared him for this incident. Although the divers technically were swimming in a part of the St. Lawrence River, they had just had a fleeting encounter with a Greenland shark, a creature of the seas that rivals the great white in size and feeds on prey as large as whales.
Gallant and Harvey-Clark, a marine biologist and veterinarian currently at the University of British Columbia, had met in 1996, when both were speakers at a scuba-diving conference in Nova Scotia. Harvey-Clark had been intrigued for years by reports of anglers who, while ice fishing on tributaries of the St. Lawrence, landed Greenland sharks. He had been carrying with him since age 11 a news clipping about Greenland sharks caught in Quebec’s Saguenay River. He and Gallant wanted to be the first divers to study these sharks in their native habitat.
Preferring waters from below freezing to 54 degrees F, Greenland sharks inhabit the depths of the Atlantic to at least 7,200 feet and swim under the polar ice cap. Although reported off Georgia and in the South Atlantic, they are generally associated with the High Arctic. An ammonia-like compound in the shark’s flesh, which renders the meat toxic to humans when fresh, apparently functions as an antifreeze.
Slow swimming speed and an inability to raise their body temperature above that of the icy waters in which they swim implies an extremely low metabolic rate and raises the question of how the sharks capture enough food to reach up to 24 feet long. Part of the answer may be the species’ exceptionally slow growth rate—about a half inch per year in one study—suggesting that a large specimen could be more than 200 years old and that Greenland sharks may rank among the longest-lived vertebrates.
Assuming that the sharks would rise to near-surface waters during colder months, Harvey-Clark and Gallant mounted their first expeditions to the Saguenay in the dead of winter. These efforts were funded by themselves and in part by the Discovery Canada science magazine program, Parks Canada and SEPAQ, a government agency established to operate and develop natural sites and tourist facilities in Quebec. The divers in 2001 and 2002 dragged generators, compressors, shark cages, tents, lights and other equipment out onto 2-foot-thick ice. Fierce snow storms buried their camps, blew away tents and dropped temperatures to minus 58 degrees F. The divers plunged through ice holes into total darkness, with visibility limited to the penetration of underwater lights. Even using bait, they failed to find a single shark. “It was profoundly disappointing,” Harvey-Clark says. “We were beat, physically and mentally.”
Discouraged, their funds exhausted, the two explorers suspended their ambition of meeting Greenland sharks on their own turf, as it were. Then, in May 2003, Gallant received emails from Silvain Sirois and Alain Simard, Quebecois divers who claimed to have seen large fish in the St. Lawrence Estuary. Arriving at the site a few days later, Gallant and Harvey-Clark found fortune embracing them: They were approached by Greenland sharks on every dive within minutes of entering the water. “It was phenomenal,” Harvey-Clark says. “It was like finding the elephants’ graveyard.”
The divers found that although the sharks swim languidly, they can turn and accelerate suddenly. These are not just sluggish, scent-oriented scavengers; they are active, curious and visually acute predators that consume nearly every sort of living matter in their environment, from relatively immobile bottom-dwelling organisms, such as seaweed and crabs, to more active creatures of the depths, such as eels, halibut and skates. “They can take a five kilogram [10 pound] chunk out of a whale like an ice cream scoop,” Harvey-Clark says. The sharks reportedly have even stalked humans walking on pack ice in the St. Lawrence. “What’s astounding is that they are active predators in water that’s only about 1 degree Celsius [barely above freezing],” says Harvey-Clark.
In summer 2004, intent on marking sharks with electronic tags, the researchers returned to the same site to find it enveloped in muddy water with visibility extending only an arm’s length. Yet just 90 seconds after hitting the bottom, Harvey-Clark says, “I looked up right in the face of a 10-foot Greenland shark. It made a pretty concerted rush at me, then veered off. It was a ‘eureka!’ moment. We almost always find seal parts in the sharks’ stomachs and wondered how they catch such fast-moving prey. I’d basically just had a seal’s-eye experience of how that happens.”
They first marked eight sharks with hydroacoustic tags, which broadcast location, depth and water temperature. Two of the sharks spent nights searching the water column, while staying closer to the bottom by day. One shark repeatedly went up to within 33 feet of the surface every 30 to 40 minutes between 4 p.m. and 5 a.m., possibly a strategy for ambushing seals.
Later, the divers tagged two sharks with pop-up satellite tags, which collect data and eventually come free and float, or pop, to the surface, where they transmit the data to a satellite for subsequent downloading to a computer. One of these sharks was only 3 miles from the tagging site after three months, while the other swam 65 miles upriver nearly to Tadoussac, where the tag popped up from a depth of more than 1,000 feet. Tadoussac is a whale-watching center and feeding ground for blue, finback, minke and other whales. Harvey-Clark speculates that the shark “probably went up to feed on marine mammals, which are very abundant in that area.”
There are risks to living in a heavily used and polluted waterway. A shark captured in the St. Lawrence in 2006 was contaminated with PCBs, flame retardants, stain repellents and heavy metals. Extensive body scarring is consistent with fishing-gear entanglement. Whether populations are threatened by human activities is unknown, but Harvey-Clark suspects that fishing gear is a prime cause of mortality. Greenland sharks are listed as “near threatened” on the IUCN red list and by the U.N.’s Food and Agriculture Organization as “especially vulnerable to overfishing.”
To continue their research, Gallant founded the Greenland Shark and Elasmobranch Education and Research Group in 2005, with Harvey-Clark as codirector. Each discovery raises more questions. Harvey-Clark relishes the difficulty of uncovering the shark’s secrets, quoting Steinbeck: “An ocean without its unnamed monsters would be like a completely dreamless sleep.”
Doug Perrine wrote about whale sharks in the December/January 2008 National Wildlife. For more information on Greenland sharks, visit www.geerg.ca.
Up a Creek with Sharks
Although sharks typically are associated with saltwater, several species in addition to the Greenland shark frequent freshwater. Best known of these is the bull shark, a widespread oceanic species that has been found more than 2,200 miles up the Amazon River and, in the wake of Hurricane Katrina, turned up in Lake Pontchartrain, north of New Orleans. It is one of three sharks most likely to attack humans. Females grow up to 13 feet long and 700 pounds; males are less than half that size.
Six species of river shark, all members of the genus Glyphis, live exclusively or primarily in freshwater in Asia and Australia. Though most of them grow up to 6 or 7 feet long, they are virtually unknown to science. The Irrawaddy River shark, for example, is limited to only one specimen, collected in Rangoon.