Can you give some examples of animal mysteries that have been solved?

 The animal kingdom is full of perplexing unsolved mysteries - I wrote a book about one of them! - But it’s just as rife with cases that finally were cracked. In this answer, we’ll sift through the paper files shelved deep in the archives of zoology, and revisit a chilling, real-life animal murder mystery.

The story of this case begins in a rather unexpected location: Sable Island. A tiny crescent-shaped spit of sand, surrounded on all sides by choppy North Atlantic waves, hundreds of kilometres away from the nearest mainland: Nova Scotia, Canada. Sable is most famous for its peculiar wild horses, but its foggy shores are also a haven for thousands of grey seals and harbour seals.

Unfortunately, their island paradise is seemingly not without its perils. In the 1990s, scientists started noticing that dead harbour seals washing up on the beaches had been mutilated in the most bizarre way; in “corkscrew” fashion. A strip of skin and blubber had been removed clean off the bone, leaving a wound that spiraled diagonally from the head to the pelvis.

I won’t include any actual photos of the poor seals in this answer, because they are very upsetting, but this diagram gives you an idea of what was removed:

The first researcher to notice this bizarre pattern of deaths was Zoe Lucas. She combed the Sable shores meticulously, and within a few years documented a staggering 4,000 washed up corkscrew seals! The island had no Internet service (even phone service is hard to come by there to this day) so she hand-wrote letters to every shark expert she could think of, asking if they knew of a shark which could perform such a macabre assault. None of them had seen anything like it.

Years later, the plot thickened. More corkscrew seals started turning up, but this time on Scotland’s Isle of Tay, more than 4,000 kilometres away from Sable Island! This area, too, was known for its rich colonies of harbour seals and grey seals.

When British scientists came upon these mysterious carcasses, they had a different killer in mind: boats. Wounds inflicted by sharks, they reasoned, are typically jagged tears. The eerily neat cuts seen on the seals could only have been made by something of human design: a propeller, for example.

Scotland’s resident Sea Mammal Research Unit came up with an incredible experiment to test this hypothesis. They created miniature model seals, with varying sizes! Each model contained a core of silicone, meant to represent the inner organs and muscles and such. This core was dipped in molten wax until it was coated in a layer of the stuff, perfectly mimicking the layer of blubber around a seal’s body.

The scientists then put these models in glass tanks, filled with water, and passed them through moving mini propellers! They ran separate tests on each major type of propeller that could be found on boats in the local area, to investigate if any of them might inflict those awful corkscrew wounds.

The first propeller type - the VSP, or Voith-Schneider Propeller - seemed only to cause superficial injury and bruising. Clearly, they were not to blame.

When the open propeller was tested, the results were more severe. This time, the blubber layer was getting sliced up, sustaining lesions which would doubtless be fatal to an actual seal. However, they had no spiral pattern, so clearly open boat propellers weren’t the culprit either.

The final experiment saw the models sent into a ducted propeller. In this type, the rotating blades are enclosed within a metal tube. Sure enough, the elusive corkscrew was finally produced! In an open propeller, the seal is evidently deflected away before the rotor does much.

With a ducted propeller, on the other hand, the poor creature is held against the rotor by the walls of the tube, so a winding slice is cut right around its body. Me being the lifetime adorer of seals that I am, it’s far from a pleasant thing to think about.

In Scotland, the case seemed as good as closed. However, just as the researchers were adding finishing touches, getting ready to publish their impressive propeller study, a new scientific paper emerged from all the way across the Atlantic, back on Sable Island. Its author was Zoe Lucas, who we mentioned earlier, and much to their surprise, it threw the whole propeller idea into question.

Sable Island is a protected area; there are no ships allowed anywhere near its shores. No ships means no propellers, and yet the exact same kind of corkscrew wounds had cropped up on the island in their thousands. What’s more, it seemed dubious that so many seals - notoriously skittish creatures - would let themselves end up between propeller blades, given how deafeningly loud they are. Lucas proposed another murder suspect…

The Greenland shark. I could go on for pages and pages about this species - indeed I have, in the past - but for now suffice it to say that it is an extraordinarily unique kind of shark. Greenland sharks are enormous, deep-sea-dwelling, and almost universally blind, with a curious preference for cold Arctic waters. They swim so slowly you wouldn’t even notice one moving if it was right in front of you, and yet somehow they are apex predators.

As I said earlier, the corkscrew seals look nothing like regular shark victims, but the Greenland shark is no regular shark. Its teeth are not adapted for cutting; rather, they’re built to grasp and tear. If they got a grip on the seal’s blubber, the shark would need only a bit of violent head-shaking to start removing it. Why the corkscrew pattern? One first has to understand the structure of blubber.

Though mainly composed of fat, seal blubber is laced with countless collagen fibres, which run diagonally around the body. If a Greenland shark was to start tearing, it’s reasonable to imagine that the rip would follow the path of least resistance, unwinding the fibres in a spiral fashion. With this in mind, Zoe Lucas concluded that the only possible culprit was this Arctic leviathan.

Unfortunately, just as the Scottish theory couldn’t explain what was happening on Sable Island, her Sable Island theory couldn’t explain what was happening in Scotland. Heated by the Gulf Stream, Scottish waters are far too warm for Greenland sharks. The authors of the propeller experiments stuck to their guns, and even managed to get the UK government to officially advise the shipping industry to shun the use of ducted propellers.

Then, all of a sudden, new evidence emerged out of nowhere, and it appeared to be a fatal blow to both theories! In 2014, Scottish researcher Amanda Bishop watched a huge male grey seal kill a fellow grey seal - a pup, who had just been weaned. He then started to eat its nutritious blubber. Bull grey seals can be extremely aggressive, but this kind of behaviour had never been observed before.

Later that day, after the belligerent male had wandered off, Bishop returned to inspect his victim. After cleaning away the blood, she discovered something amazing. Lo and behold, a perfect corkscrew pattern. The pup’s blubber had been torn away with the grain of the collagen fibres inside, exactly as described earlier.

The next step, of course, was to keep an eye on that bull. Within the week that followed, Bishop watched him commit four more killings, and every time his efforts to get at the blubber produced the exact same corkscrew pattern! It wasn’t long before his recorded victim count rose to fourteen. The havoc on Sable Island was most likely caused by a male seal with similar cannibalistic tendencies!

The serial seal killer was neither ship nor shark, but seal. Who would have thought? After decades of heated debate and dead ends, the zoological whodunit finally came to a close. So too must this answer. I know it wasn’t exactly light-hearted - I hope you guys don’t mind! To me, though grisly, it’s as interesting as any true crime story in the human world.

Thank you so much for reading, hope you enjoyed, and have a great day!