The Curious Case of the Corkscrew Killer

Brynn Devine | October 31, 2025

In the 1970s, dead seals with strange, corkscrew-shaped wounds began washing up on the shores of Sable Island, Nova Scotia, with no obvious attacker. In this story, shark expert and Oceans North Arctic Fisheries Scientist Brynn Devine revisits this morbid mystery and explores what truly happened in the case of the Corkscrew Killer.

Off the coast of Nova Scotia, nearly 300 km southeast of Halifax, lies Sable Island—a miniscule, uninhabited sandspit known for its natural beauty, as well as its resident grey and harbour seal populations. Nicknamed The Graveyard of the Atlantic, the island is also home to over 350 shipwrecks, with some dating back as early as 1583.

Image – Sable Island, known as the “Graveyard of the Atlantic” for its many shipwrecks, has become a graveyard of a different kind.

Credit – Earth Science and Remote Sensing Unit, NASA Johnson Space Center

But in the past 50 years, Sable Island has become a graveyard of a different kind. It began in the 1970s, when scientists monitoring the island’s seal colonies reported seeing dead harbour seals scattered along the shore, each with wounds suggesting a brutal attack. Although these sporadic observations persisted for decades, in 1993 the occurrences steadily increased, leading scientists to initiate a targeted annual survey that counted nearly 5000 seal corpses between 1993 and 2001.

Most of the victims were young, with both harbour and grey seals among the dead. The majority of carcasses were marred by deep cuts that wrapped or “corkscrewed” around the body. There were no jagged edges to the wounds or additional punctures; instead, they appeared as a clean cut made with surgical precision, the blubber layer torn away, even underneath the unbroken fur.

Image – A harbour seal lies on the beach of Sable Island.

With thousands of recorded victims sharing these curious wounds and no clear culprit, the hunt for the mysterious predator—nicknamed the “Corkscrew Killer” by National Geographic in 2011—was on.

Based on the condition of most carcasses, the killings seemed to be occurring very nearshore in shallow water. But what—or who—was responsible?

The majority of the wounds appeared as continuous lacerations with no teeth marks, which differ from well-documented killer whale bites on seals, ruling out this large predator as a suspect.

While propellers can cause deep, clean lacerations on marine life, with little to no boat traffic around this remote island—especially nearshore and in cold winter months—propeller strikes did not seem likely either.

This left an unidentified shark as the likely suspect, drawing the interest of several prominent shark experts who flocked to the island in search of the culprit. The mystery sparked a series of documentaries between 2003 and 2011 on networks like the Discovery Channel and National Geographic, which featured researchers searching for the species behind the gruesome attacks.

At least a dozen shark species have been observed in the waters surrounding Sable Island. However, shark experts deduced that this particular suspect had to be a large, predatory shark capable of attacking seals of that size.

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The Suspects

Removing smaller sharks less than 2 metres from the line-up, the suspect list was narrowed to the following sharks: the shortfin mako, white, porbeagle, basking, common thresher, Greenland, and blue shark.

Now, not all of these sharks are known to prey on seals. Removing species whose diet does not include seals left experts with two viable options: the white shark and Greenland shark.

Although a small percentage of the seals displayed clear evidence of a white shark attack with distinctive “slash” wounds and teeth marks, this species clearly was not responsible for the countless victims with corkscrew wounds. On top of that, the seal deaths continued throughout the year and during the cold winter months—the time of year when white sharks migrate south.

With the white shark off the table, the blame for the Corkscrew Killings quickly turned to an unusual suspect, one that doesn’t mind chilly waters: the Greenland shark.

Although often considered a deep-dwelling species, these large sharks are known to venture into shallow water when food is present. And despite their leisurely swimming speed, the remains of swift-moving prey like seals have been found in the stomachs of Greenland sharks. This fact—combined with the differences between the bite, tooth structure and feeding behaviour of white sharks—led experts to quickly attribute the seal deaths to Greenland sharks.

Case closed! Well, for a few years at least…

Over 4000 km away from Sable Island on the other side of the Atlantic Ocean, an eerily similar mystery was unfolding. For decades in the UK, Belgium, and Germany, dead seals were washing up on shores with—you guessed it—deep, corkscrew lacerations. In 2013, determined to get to the bottom of it, a team of researchers from the University of Veterinary Medicine in Hanover, Germany, began to record the seals’ habitat on video.

The cameras captured a shocking scene: large, adult male grey seals were capturing young seals and dragging them up the beach, often drowning them in shallow tidal pools and proceeding to cannibalize their victims. Following several attacks, researchers retrieved partially consumed carcasses for pathological examination, confirming the distinct “corkscrew” wounds. In 2016, researchers in the UK, where harbour and grey seal corpses had haunted beaches for years, gathered similar video evidence of grey seal attacks. With the culprit filmed in the act, the evidence was irrefutable: this was a seal-on-seal crime.

Image – Higher densities of grey seals (pictured) may increase the likelihood of both predation of harbour seals and cannibalism of their own species.

Though surprising, these findings weren’t entirely new. In 1992, researchers spotted cannibalism by grey seals on Amet Island, Nova Scotia, located in the Northumberland Strait in the Gulf of St. Lawrence. Although these scientists acknowledged that the carcasses somewhat resembled shark kills at the time, they confirmed several accounts of cannibalism by adult male grey seals during January and February of that year—around the same time the number of carcasses began increasing on Sable Island. Despite this evidence, the Greenland shark became the primary suspect as the Corkscrew Killer of Sable Island.

Years later, many still believe this species to be responsible. Although more recent studies attribute the Corkscrew Killings to seals, these findings are known primarily to the marine science community—not the general public. Those who may have learned about the incident on TV in the early 2000s likely have not heard about the victims and perpetrators since then.

It does not help their case that, thanks to negative media coverage and their public perception, sharks are often the go-to suspect for underwater attacks—certainly over charismatic marine mammals like seals.

Image – While not the most charismatic species, Greenland sharks have been vindicated in the case of the Corkscrew Killer.

Credit – Eric Ste Marie

The story doesn’t end here. Grey seal populations across the North Atlantic are increasing and many are approaching carrying capacity, or the maximum amount an ecosystem can support. Higher seal densities may increase the likelihood of both predation of harbour seals and cannibalism of their own species. That means that while the case of the Corkscrew Killer may be solved, seal killings around Sable Island–which hosts the largest breeding colony of grey seals in the world–aren’t likely to stop.

So, next time you hear about an incident like this, spread the word that Greenland sharks are innocent, and a word to the wise: it’s always the ones you least expect.

Brynn Devine is Oceans North’s Arctic Fisheries Scientist.