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Mysterious Predators of the Frozen North

Text and photography by Doug Perrine

 

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Greenland sleeper shark, Somniosus microcephalus, St . Lawrence River estuary, Canada Image #: 035452

It’s a staple of Hollywood, and the dramatic peak of many a film – that gut-wrenching, testicle-shrinking moment when the hunter realizes that he has just become the hunted. It happened in real life to Canadian diver Jeffrey Gallant when the tables turned in his multi-year quest to find an elusive giant predator in Canada’s saline rivers. When a massive dark shape passed right in front of him shortly after he landed on the bottom of the St. Lawrence Estuary in pea-soup conditions with visibility only extending an arm’s-length, Gallant understood immediately that his quarry had found him instead. He also suspected that the reason the shark had chosen to inspect him might be related to its dietary habits, which are known to include large mammals.

Gallant and his expedition partner, veterinarian Dr. Chris Harvey-Clark, had both been intrigued for years by the occasional news reports of Canadian anglers landing an unexpectedly large catch while ice-fishing – a Greenland shark, Somniosus microcephalus. Greenland sharks belong to the family of sleeper sharks, named for their sluggish behavior, and are related to dogfish sharks. Preferring frigid waters from below freezing to about 12 C / 54 F, Greenland sharks inhabit the depths of the Atlantic to at least 2200 m / 7200 ft, and swim under the polar ice cap. Their slow swimming pace, the minimal resistance they put up when captured, and inability to raise their body temperature above that of the icy waters in which they swim leads to the supposition that they have an extremely low metabolic rate, and raises the question of how they capture enough food to grow to lengths of up to 7.3 m / 24 feet – larger than a great white shark. Part of the answer may be an extremely slow growth rate – about 1/4 inch (0.5 cm) per year in one study – leading to estimates that a 7 m specimen could be over 200 years old, making Greenland sharks possibly the longest-lived vertebrates on the planet.

The stomach contents of captured Greenland sharks have included a variety of fish and invertebrates, sharks (including their own kind) skates, birds, seals, a dog, a horse, a reindeer, polar bear parts, porpoise, beluga, and narwhal. It’s possible that much of their food is scavenged as carrion, but there is also evidence that they can be active predators, leaping out of the water to ambush caribou drinking at river mouths according to one account. They are suspected of being the agent responsible for stripping the blubber off of seals in a corkscrew pattern. It is even claimed that they have stalked humans walking on pack ice. The dentition of the Greenland shark is clearly well-suited for disassembling large prey. The upper teeth are pointed and function as the “fork” to hold the food item, while the angled lower teeth function as the “knife” to saw off pieces for consumption. “What’s astounding about these animals,” says Harvey-Clark, “is that they are active predators in water that’s only about one degree Celsius. They’re kind of like ‘Dawn of the Dead’ sharks. How do they catch large, fast-moving prey?”

Added to the mystery of how such a slow-moving zombie-like animal captures such agile prey is the question of how it is affected by its curious relationship with the copepod, Ommatokoita elongata. This crustacean parasite is found on both eyes of most Greenland sharks, and feeds on the corneal tissue, scarring the eyes. It is presumed that the sharks become nearly blind as a result. There is some speculation that the parasites might benefit the shark by attracting small prey, but this has never been demonstrated. It’s hard to imagine how blindness could be an advantage in hunting seals. At the same time it’s not at all comforting, when diving in near-zero visibility, to know that you are in the presence of a gigantic predator that has no need of vision to satisfy its appetite. Vision is likely of little use in the dark ocean depths frequently inhabited by Greenland sharks.

Although Greenland sharks have been reported as far south as Georgia, and even into the South Atlantic, they are generally associated with the high arctic. The Inuit feed the flesh of the sharks to their sled dogs, but only after it has been boiled in several changes of water, or buried and fermented for several months. Greenland shark meat contains high levels of an ammonia-like compound which is toxic if eaten fresh. Dogs that have eaten fresh shark meat may fall into a “drunken” stupor and be unable to stand. A large enough dose can cause convulsions and death. The fermented flesh is considered a delicacy in Iceland. The chemical which renders the flesh toxic apparently functions as an antifreeze/ preservative to protect the sharks’ bodies from the freezing temperatures and crushing pressures (up to 3300 psi or 9700 kg per sq cm) at the great depths they inhabit.

Since these sharks were believed to live primarily in the frigid waters of the deep sea and high Arctic, Harvey-Clark’s imagination was fired by a news story of a fisherman landing one in the Saguinay River in Quebec, almost 3,000 km (1864 miles) from their supposed home territory of Greenland. When he met Gallant, a bilingual native of Quebec, he asked him to investigate. Gallant soon found that stories of giant sharks were common among the French-speaking fishermen of Quebec – dating back to a 16th century account of a sailor bleeding to death after having his leg bitten off while swimming in the Saint Lawrence River. These tales had just never crossed the language barrier into English-speaking Canada, where Harvey-Clark was employed at Dalhousie University in Nova Scotia. In the world of academia, the Greenland shark was, and remains, a “black box species” – with almost nothing known of its natural history.

Following the conventional wisdom that the cold-loving sharks would most commonly rise to near-surface waters during the colder months, Harvey-Clark and Gallant mounted their first expeditions to search for sharks in the Saguenay Fjord in the dead of winter. Normally this tributary of the St. Lawrence has warmer fresh water flowing on top of the colder, denser saltwater below. When the surface freezes, however, the thermocline is inverted with the fresh water on top becoming colder than the deep water. This is when the cold-loving Greenland sharks should rise to shallow depths where they could be observed, they reasoned. Their research determined that sharks were caught every year at a giant ice-fishing camp that convenes each winter at the head of the Fjord, so this is where they concentrated their efforts, dragging generators, air compressors, shark cages, tents, lights, and all the other equipment needed out onto the two-foot thick ice.

During two winters, in 2001 and 2002, they battled fierce storms that buried their camps in snow, blew their tents away and dropped temperatures to -32 C / -26 F (-50 C / -58 F wind chill factor). The bitter cold resulted in frost-bitten fingers and caused plastic items to shatter and their regulators to freeze up and free-flow. Diving through holes in the ice in near-darkness, with visibility limited by the penetration of their underwater lights, they had no idea what to expect. “In most cases, when you are preparing to dive with a large and potentially dangerous animal,” says Harvey-Clark, “somebody else has already been in the water with the animal you are going to dive with. In this case, nobody had.” In the end, they were unable to see any sharks, or even to attract any by hanging baits in the water.

Discouraged, and having exhausted their funding, the two explorers had to shelve their ambitions of being the first to study and film Greenland sharks swimming freely in their natural habitat. “Looking for Greenland sharks in Canada has been a bit like looking for Bigfoot,” said Harvey-Clark. Then, in late May of 2003, Gallant received an e-mail from Silvain Sirois, a Quebecois diver who claimed to have just seen a fish bigger than himself while diving in the St. Lawrence at the Baie du Garde Feu. Gallant was dubious. On June 1, he received another e-mail from a friend of Sirois, Alain Simard, who said that he had seen a shark on each of three consecutive dives in the nearby Baie St. Pancrace. When Gallant called Harvey-Clark with the news, he asked “Why aren’t you there?”

They both loaded their gear and headed to the site, but Gallant, being closer, arrived a day earlier. Entering the water, he was approached by a Greenland shark within minutes. This happened on every dive, and was repeated the next day with Harvey-Clark, as well. One of the first things that the researchers noticed was that these sharks did not, for the most part, carry the eye parasites that afflict nearly all Greenland sharks in the arctic. Furthermore, they seemed to follow the divers with their eyes. They normally moved slowly, but could turn and accelerate suddenly when spooked and could easily out-maneuver and out-swim the divers. They realized that this was not the sluggish, blind, scent-oriented scavenger which had been conjectured, but rather an active, curious, visually acute, and highly-capable predator. The sharks were clearly on active patrol and investigating any new entry into their environment. This was not a comforting thought the following year when the visibility dropped from poor to non-existent, and the team was not aware of the approaching sharks until they arrived within touching distance. It also made the divers more than a little nervous when they ran low on air and had to ascend, and found sharks following them all the way to the surface. Were they merely being watched, or stalked?

The records of stomach contents of captured Greenland sharks only offered more confusion in regards to what sort of behavior to expect from them. In essence they consume nearly every sort of living matter in their environment, including bottom-dwelling organisms such as seaweed, sea urchins, marine snails, crabs, amphipods, brittle stars, sculpins, spiny eels, halibut, wolf-fish, lumpfish, cod, and skates and their egg cases. The white scars on the snouts of many Greenland sharks observed in the St. Lawrence might be indicative of active feeding on prey sheltering among bottom structures and perhaps of rooting for prey in the bottom sediments. However, stomach contents also contain a good representation of organisms that inhabit the water column and surface waters, including salmon, pollock, haddock, redfish, herring, char, smelt, squid, jellyfish, sea birds, seals, horses, reindeer, and cetaceans of all sizes. The whales and land mammals are probably mostly scavenged as carrion, but there is some evidence that seals are taken alive, especially around Sable Island, a major breeding ground for gray seals and harbor seals. One shark had three sets of hind limbs of gray seals in its stomach. The best assessment the researchers could make was that these are extremely broad-spectrum predator / scavengers – able and willing to consume nearly anything they could get their mouths around. “They…can take a five kilogram chunk out of a whale like an ice cream scoop,” says Harvey-Clark, “but they can also suck up a large flounder like a vacuum cleaner. It gives you pause when you are diving with them.”

As one of the largest sharks in the ocean, rivaling the great white in size, and by far the largest fish in polar waters, these indiscriminate feeding habits should make the Greenland shark potentially as dangerous to humans as the tiger shark – another indiscriminate feeder, responsible for a large number of attacks on humans. Could it be that the lack of records of attacks (only one unconfirmed report of a human leg in a shark stomach from 1859, and one supposed 16th century attack) is merely a result of the shortage of humans to be found at great depths in the ocean and under the ice during the Arctic winter? The discovery by Sirois and his companions of Greenland sharks in shallow water in the St. Lawrence during the summer raised disturbing questions as to whether this balance sheet might suddenly change. Scuba divers had been exploring these sites for years without seeing sharks before yet now they were seeing them regularly for weeks at a time. Furthermore, in the following years, the peak of shark sightings switched from June to July and into August – the warmest months, when Quebecois and visitors to the province enjoy swimming, skiing, and other water sports.

As always with scientific investigation, each new discovery raised more questions. Do the St. Lawrence sharks form a separate population from the ones found in the arctic? The low incidence of eye parasites strongly indicate that they might. Where do the sharks go during most of the year when divers are not seeing them? Why are they coming into shallow water during the warmer months – exactly the opposite of what was expected? The first year divers noted an unusual abundance of capelin fish in the bay where the sharks were sighted, but this correlation did not always hold in subsequent years. Intriguingly, three times as many female as male sharks were recorded by the divers.

To further their research efforts and disseminate their findings, Gallant and Harvey-Clark founded the Greenland Shark and Elasmobranch Education and Research Group or GEERG (www.geerg.ca). The first three sharks tagged stayed within the St. Lawrence system for the three months that the tags were operational, although one moved 115 km (71 miles) up the river. Two of the sharks spent the nocturnal hours searching the water column, while staying closer to the bottom during the day. One shark regularly went up to within 10m (33 ft) of the surface between the hours of 4pm and 5am. Could this be a strategy for ambushing juvenile seals? If so, there are strong implications for the advisability of taking a late afternoon swim in the river.

Of two sharks subsequently tagged with pop-up satellite tags, one only moved 5 km away over a period of three months, while the the other swam 100 km upriver to the Tadoussac area, where the tag popped up from a depth of over 1,000 feet. Tadoussac is at the center of Quebec’s whale-watching industry and is a 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 implications for the sharks of living and feeding in this heavily used and polluted waterway. A Greenland shark captured in the Saguenay in 2006 was found to have its flesh and organs contaminated with PCBs, flame retardants, stain repellents, and heavy metals. Extensive body scarring is consistent with interactions with crab pots and other fishing gear. Whether populations are threatened by pollution or human activities is unknown, but Harvey-Clark suspects that fishing gear interaction is one of the biggest causes of mortality in the species. Officially Greenland sharks are listed as Near Threatened on the IUCN redlist. They are categorized by the FAO as a species with life history characteristics that make it especially vulnerable to overfishing. As many as 50,000 a year were reportedly harvested for their oil in the 1940s, before Vitamin A was synthesized, and they are still taken in Greenland and Norway, with the oil being processed as a fine machine oil. Inuit take at least few hundred a year. The status of worldwide populations, like most of the basic biological characteristics of this elusive giant predator remain mysterious. In spite of his determination to crack the shark’s secrets Harvey-Clark relishes the difficulty of the task, quoting Steinbeck: “An ocean without its unnamed monsters would be like a completely dreamless sleep.”