It's a mammalian mystery that would baffle even Sherlock Holmes: the unexplained deaths of dozens of seals, found washed-up off the coasts of Norfolk, St Andrews and the Firths of Forth and Tay, their bodies horribly lacerated.
Seven common and grey seals – their corpses torn by a single, deep, corkscrewing cut – have been found in Scotland over the last two months, prompting an urgent investigation by the Sea Mammal Research Unit (SMRU) at St Andrews University. And in Norfolk, police are working with the RSPCA to rule out foul play in the deaths of at least 20 other seals, discovered with similar injuries since last November.
So what monster of the deep is to blame? Suggestions posted by amateur sleuths on online message boards range from a stray "cookiecutter" shark (this grim predator takes hold of its prey and spins it round – but as the shark usually inhabits tropical waters, it's unlikely to have strayed into the North Sea), to the ventilator on a naval submarine, a ship's propeller, or an underwater wave-power turbine.
According to Gill Bell of the Marine Conservation Society, an underwater blade is the most likely culprit. "Most seals are very wary of propellers," she says. "But the seals may have been caught in the draft of a powerful current, and been dragged through a rotating blade." The scientists at the SMRU stress that their investigations are still under way – but agree that the blame is unlikely to fall on a marine predator. "If it was a shark killing these seals," says researcher Callan Duck, "it would need to have just one tooth, and one jaw, to cause this kind of single, spiralling cut – which just isn't possible."
Duck is reluctant, as yet, to "play the blame game"; but he says that the more likely culprit is a "cowled thruster" – a caged propeller used by ships, such as oil-rig support vessels and tugs, that need to remain stationary in the water for long periods. The seals could have swum close to such a propeller, and met a gruesome end when it was suddenly switched on.
"Most seals know what's bad for them," says Duck. "But these ones may have gone looking for fish, and then been sucked to their deaths."
Members of the public, who may have documented similar events, are being asked to send information or photographs to smruseal@st-andrews.ac.uk, or by calling 01334 462 630
