Codenamed Seal Ripper: The scientists are perplexed

Dead seals are turning up on beaches around Sable Island

Marine biologists and fishermen alike are confounded

The attacks appear to be the work of a shark

But, the forensic evidence cannot pinpoint the perpetrator

Muscle-bound Shark

Seal Ripper

It has long been thought that Greenland sharks were mild-mannered scavengers, but recent research has revealed that these mysterious creatures are actually apex predators.

Kit Kovacs and her team set out to learn more about the diet of Greenland sharks in Svalbard, Norway’s northernmost settlement. Through their research, they discovered that not only do Greenland sharks feed on large fish like cod and billfish, but also harbour seals – a startling revelation that proves once and for all that this species is an active predator.

But how could such a slow-moving creature successfully hunt down something as fast and alert as a seal? Join us as we explore the strange behaviour of the Greenland shark to uncover its secrets!

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The Naturalist

Naturalist Zoe Lucas lives and works on the remote Sable Island. She’s monitored the seal population here for almost 20 years but she has never seen anything like this. The attacks of the alleged Seal Ripper are a mystery.

Zoe Lucas “At first, when I looked at these animals I was still thinking of it as the skin being peeled off the body”

As Lucas examined the corpse it was clear that the wounds were bizarre.

Zoe Lucas “The wounds were absolutely clean-edged as if made with a knife, no jagged edges, no serrated marks along the wound edge. And, in most cases, no puncture marks at all.”

The seal’s flesh is cut around its body unravelling its carcass as a corkscrew. Over the winter Lucas discovers more dead, lacerated seals. Bizarrely, the wounds are in the same corkscrew pattern. After a year, the body count has risen to 95 mutilated bodies.

Killings most Bizarre

Lucas “More than 65% of these injuries occur during January and February.”

Each winter, she finds the same pattern occurring. Only some sections of body tissue have been removed from the seals.

Zoe Lucas “The whole blubber layer was torn away from the carcass”

The next year she counts 275 victims.

Lucas “There was a dramatic increase in those first years when when I was doing beach surveys”

Sable Island lies 160 km off the coast of Nova Scotia. Here, the grey seal breeding population is the largest in the world. Seals hold a vital link in the ocean ecosystem. Many of the victims are young seals. This series of attacks is tearing through Sable Island’s grey seal population.

Harbour seals too are under threat. Each year fewer and fewer seal pups are born. This mysterious killer seems intent on wiping them out.

Zoe Lucas Naturalist

Lucas must find out who, or what is causing this carnage. One of her first suspects is the killer whale, a well-known seal predator. Could they be hunting around Sable Island?

Zoe Lucas “It’s conceivable that a killer whale might be able to kill seals in this area.”

With an endless supply of fat seals on offer. The island would make a fertile killing ground, but killer whale experts don’t believe that they would make such clinical wounds.

Lucas “Fishermen have, of course, a negative relationship with seals”

Zoe Lucas Naturalist
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Fishing Boat Damage

The wounds, may not be deliberate, perhaps the propellers on fishermen’s boats could cause such injuries.

Lucas “We don’t have vessels this close to Sable, some of these animals were killed very close to shore, within this zone I would find animals that were freshly killed, that blood was still flowing and if I thrust my hand into the body they were still warm.”

Lucas’s enquiry turns towards another threat altogether.

Lucas “The only cause for these injuries had to be some kind of a predator and that was probably sharks. But the question is, what were the sharks doing, how was it attacking the seals to cause these kinds of injuries and what species of shark was involved?”

Zoe Lucas is no shark expert. With the seals’ death toll rising relentlessly, she calls out for help. She sends images of the wounds out to the world’s leading shark experts.

Shark Experts

The mystery of the Sable Island Seal Ripper goes global.

Shark experts across the world analyse the pictures, but the wounds are unlike anything that any of them have seen before.

Dr Chris Harvey-Clark from the University of British Columbia “What is doing the slashing? I certainly wouldn’t want to be swimming around in the surf when these are washing in.”

Dr Lisa Natanson of the National Marine Fisheries Services “The wounds she was showing us, basically, were seals that were skinned on the beach and that didn’t look like any kind of shark that we had seen”

But, if the killer isn’t a shark, what could be large enough, aggressive enough, and have the physical ability to mutilate so many victims?

By 1998, there have been 2360 recorded victims, no-one can find the cause of their brutal deaths.

Dr Chris Harvey-Clark

At the Apex Predators lab in Rhode Island, Natanson focuses on how the seal’s skin has been peeled off.

Natanson “When I first saw the wounds, they are striking, completely different from your normal shark attack where you have the half-moon bite”

Natanson begins to draw up a list of shark suspects. For a shark to cause this kind of damage to seal it has to be huge. There are three predatory sharks in the area big enough to take on a seal that can weigh 300 kilos. The Tiger, the Mako and the Great White.

Natanson “Those animals take a big chunk out. It’s gonna leave a ragged edge”

Dr Chris Harvey Clark
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Great White Shark

Canadian marine biologist Chris Harvey-Clark has studied sharks for over 15 years. He believes the Great White can’t be ruled out as a suspect.

Harvey Clark “Great Whites are quite happy right down to temperatures in the 50s. They do just fine, they are big, eat a lot, have a high metabolic rate, and have all kinds of physiological adaptations to retain heat so, they’ve got the hardware to be a wintertime Hunter around Sable.

If you look south of Sable off the New York Bight, it’s a Great White Pupping area and, as they approach eight or nine feet in length they make a transition from being, primarily, fish-eaters to being, primarily, mammal-hunters. An island with 100,000 seals on it and a lot of them junior and predator-naive, that might be my pick”

The wounds Lucas is finding have never been seen before. With the investigations stalled, Natanson’s team offers up another suspect, a shark that is the polar opposite of the Great White, this shark is known as the deep-water slow-moving scavenger. The Greenland shark.

Greenland Shark

Naturalist, Lucas hunts for all the information about this shark that she can find.

Lucas “That set me off on a better direction, a more focused direction, and then I was able to track down old papers on the species and start asking people more specific questions”

But, there is little information to be found. Researchers have overlooked the Greenland shark because it is so difficult to observe. It inhabits the cold, dark depths of the North Atlantic.

Natanson “At the time this whole thing started, the Greenland shark was a very unknown shark, there wasn’t a lot of work done on it. We thought they were very sluggish, we didn’t think they really came up to the surface and one wouldn’t expect them that close to Sable Island, which is a very shallow sandbar.”

These sharks are known as deepwater scavengers, whatever is killing the seals is a shallow-water predator. Everything Lucas finds in the scientific literature enhances the Sable Island Seal Ripper.

Dr Lisa Natanson

Baffin Island in the Canadian Arctic.

Marine biologist Greg Skomal of the Massachusetts Shark Research Program is risking his life going under the ice to be one of the first scientists to dive with the Greenland shark.

Greg “Going under the ice, and diving with them, was a pivotal moment in my life, it was not only the most frightening thing I’ve done, but it was the most awe-inspiring. The first thing that jumped out at me was that this is a very attractive shark, with it’s a cigar with fins.”

Skomal is determined to discover as much as he can about this creature’s behaviour.

Dr Lisa Natanson
Dr Lisa Natanson

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Greg Skomal

Skomal is determined to discover as much as he can about this creature’s behaviour.

Greg Skomal “I think that it’s the fact that it is shrouded in so much mystery that I find awe-inspiring”

During the dive, Skomal observes something wrong with the shark’s eyes.

Greg Skomal “I knew when I jumped in the water and saw those eyes, that those fish couldn’t see me all that well.”

A small crustacean called a Copepod is attached to the shark’s eye by tiny hooks.

Skomal’s colleague George Benz is intrigued.

George Benz “We would catch these sharks, we would haul them to the surface and these copepods were quite evident on all the fish that we captured”

Benz removes some of the shark’s eyes for analysis. He’s shocked by what he discovers.

Shock Discovery

George Benz “Basically, these copepods have got the ability to cause lesions in the eye to the point where it impairs the shark’s vision. Some of the sharks, probably, are approaching blindness in the way that the eye no longer functions as an image-forming camera.”

Their evidence seems to cast still more doubt on the suspicion that the Greenland shark is the Sable Island Seal Ripper.

Even if this shark came into shallow water, it appears that it wouldn’t be able to locate the seals, let alone kill them. Being a very nearly blind scavenger, it could only feed on the seals if they were already wounded or weakened.

Laboratory experiments offer an exciting development.

Chris Harvey-Clark “It’s got nostrils like shotgun barrels and when you dissect them, the nerves from the olfactory are thicker than the nerves from the eyes. There is more information coming in from the nose than there is from the eyes.”

Breaking the Ice

But, to discover the true nature of the shark, Harvey-Clark knows he has to dive with it, in its natural environment. First, he needs to find this elusive species. He and his research partner Jeff Gallant searched the frozen waters of the St Lawrence estuary in Québec.

Setting up camp on the ice, they drill holes and bait lines. Then, round-the-clock they make repeated dives into the dark, freezing-cold water. But, they can’t find any sharks.

Hope comes, however, from an unexpected tip-off. Gallant’s contacts sight a strange shark in the nearby bay: St Pancras

Greg Skomal
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Jeff Gallant “Out of the blue in 2003, I got an e-mail from a friend who said that while he was anchoring at this dock that they’re in right now a shark had buzzed by him”

For Harvey-Clark and Gallant this is a far-cry from the dangers and disappointments of the St Lawrence expeditions. It is summer and the creature swimming in the shallow water of the estuary is a Greenland shark.

During the winter of 2009, the death tally on Sable Island hits 5000 but the killer’s trail runs cold.

Naturalist Zoe Lucas continues to collect evidence but she’s no closer to finding the truth.

Nearly 5000 km away in fjords around Svalbard in Norway, seals begin to, mysteriously, disappear.

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Svalbard, Norway

Kit Kovacs has been studying harbour seals here for the past decade. Recently, both young and old have been disappearing. Are these copycat killings?

Dr Kit Kovacs “This population had a very truncated age population. The oldest individual we caught was 17 years of age. But in harbour seals, normally, we’re over 30 years.”

For Kovacs the list of potential predators is very short.

Kit Kovacs “Looking broadly at what could possibly be a predator of harbour seals in Svalbard there are only three real candidates. Polar bears, killer whales and sharks. And the sharks in these waters are Greenland sharks”

Kovacs and her team set a series of baited lines in the fjord to capture the Greenland sharks. The fjord is full of Greenland sharks.

Kovacs is helped by marine biologist Lisa Leclerc. Together they dissected the sharks they had caught to check the stomach contents.

Lisa Leclerc

Kit Kovacs “The first thing that was really surprising about the stomach contents was the amount of large fish. These sharks are eating metre-long bull fish, metre-long cod. When we fish in the fjord, for scientific purposes, we never see fish that large.”

Greenland sharks are predators and their diet is not limited to fish. The evidence is conclusive and startling. In the fjords of Norway Greenland sharks are feeding on seals. But are the sharks feeding on live seals? The presence of tiny animals called amphipods in the seals’ flesh would indicate the seals were dead when they were eaten.

Kovacs “In Svalbard waters carnivorous amphipods attach onto dead items very rapidly. They’re onto the eyes within minutes.”

If there are no amphipods, the seals were alive when the shark consumed them. And if alive, this will prove, once and for all, that the Greenland shark is a predator.

After decades, the myth that Greenland sharks are mild-mannered scavengers is shattered. The discovery supports Lisa Natanson’s hypothesis.

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Unique Dental Pattern

Lisa Natanson “It’s definitely an active predator, it is well up on the active predation level.”

Natanson wants to work out if the Greenland Shark’s teeth could cause a corkscrew-shaped wound. Unlike the jaws of a Mako or a Great White which consist of two rows of teeth which rip and tear, the Greenland shark teeth are truly strange.

On the upper jaw is a row of tiny pin-like teeth that are too small to cause real damage. The teeth on the bottom jaw are small flat blades that are so closely overlapped, they form a saw.

Natanson “If we can recreate that cut then we know that mechanically those teeth can make that cut. Demonstrates that this jaw type can make this smooth wound which is the same as any part of the cut on this carcass”

Lisa Leclerc
Lisa Leclerc

Shark's Teeth

With a sawing action, Natanson can make the teeth slice through the seal’s flesh. But, to rip the seal around its body, corkscrew shape, she would have to repeatedly rotate and contort the jaw. This is not the way a shark normally attacks and mutilates its prey. How could this shark so clinically unravel the flesh of so many seals? In a pattern repeated thousands of times along the coast of Sable Island.

In Massachusetts Marine biologists George Benz and Greg Skomal revisit footage taken during their dive on Baffin Island. They are trying to cast light on the strangest shark bite in the sea.

Could this reveal how the Greenland shark attack might lead to the weird corkscrew injuries found on Sable Island?

George Benz and Greg Skomal are analysing rere footage they’ve shot in the deep water around Baffin Island.

Greg Skomal “You get a rare opportunity to get a glimpse of an animal that lives in 500 feet of water in pitch blackness using new technology”

The shark approaches out of the gloom onto the corpse by its smell. Suddenly, it lunges biting hard into the Seal.

George Benz “You can see it gets a pretty good purchase here then goes into a series of rocking motions back and forth”

It scythes through sealskin repeatedly until it reaches tissue, then, clinically it extracts a section of flesh.

Shark Summary

 

The Greenland shark’s jaw is a specialised tool. It creates deep, scalpel-like, cuts. But would this technique peel off the seal’s flesh in the corkscrew shape?

On Sable Island, another seal with corkscrew-shaped injuries washes up on the beach. On its back is a tracking device. The corkscrew wound starts at the neck but continues below the acrylic mesh that attaches the device. The wound cannot be a single cut, it has to be a tear.

It’s impossible that such a specifically shaped wound could be repeated again and again by chance. Lucas finds the answer to the puzzle lies in the anatomy of the seal itself. Collagen fibre in the skin and blubber of marine animals winds around the body at a 45° angle. After the initial cut the fibres direct the tear along the path of least resistance.

One final part of the puzzle remains. How could this slow-moving creature chase down a fast, alert seal unless it was already vulnerable?

Kit Kovacs “Seals sleep at a variety of different depths depending on the species and they are completely capable of just remaining still at any given depth”

Dr Chris Harvey-Clark “I’ve been able to swim up to a sleeping harbour seal and tap it and wake it up”

In low visibility, these sharks are using their smell sense to track down sleeping seals and then use other senses to pinpoint the exact target for an attack.

References

Seal Ripper: The Unknown Killer

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