Get the facts on Scotland's strange 'sofa shark'

From giant megamouths to jaw-dropping goblins, some truly bizarre sharks cruise the world's deep oceans. Ancient and highly specialised, these mysterious creatures posses a slew of unique adaptations for life in the depths, making them quite the spectacle when they turn up. While conducting a fish population survey off the Scottish coast recently, a team of scientists unexpectedly caught one such animal: a two-metre false catshark.

Researcher Christopher Bird photographs the shark before its release. Image: Christopher Bird/used with permission

Unofficially known as "sofa sharks" because of their flabby bodies, false catsharks (Pseudotriakis microdon) are a far cry from the Jaws trope. They spend their lives between 200 and 1,500 metres below the surface, sluggishly swimming or hovering along the sea floor. Studying deep-sea animals is no easy task, and there is a lot we don't know about these enigmatic sharks, but interestingly, they're spotted more frequently than you might think.

Several reports have claimed this shark to be "the second in a decade for Scotland", but UK marine fisheries advisor Tom Blasdale clarifies that isn't the case. "As one of the scientists who was on board, I feel I should correct this," he says. "We actually have seen this species before in Scottish waters, quite a few times. It's still an interesting fish to see, though! And I hope its new name, the 'sofa shark', sticks!"

Being an "oceanic couch potato" isn't the worst label that's been pinned on false catsharks over the years. The species was also dubbed "the sea goat" after a specimen in the Canary Islands was found to have a pear, potatoes, a plastic bag and a soda can inside its stomach (way to go, humans). This, combined with other intestinal finds like pufferfish spines, has led scientists to believe that the slow-going sharks indulge in scavenging from time to time.

Image: NOAA Okeanos/Wikimedia Commons

When they're not chowing on leftovers, sofa sharks mainly feed on bony fish, smaller sharks and squid. If you're wondering how a slow predator could land such quick prey, it's a good question. The most likely explanation is that, like Greenland sharks, false catsharks are capable of quick bursts of speed when they need a bit of a boost.

We don't actually know how big these animals can get, but since the largest specimen ever caught measured just under three metres, the Scottish shark was truly quite the find. "It took three of us to get it off the fish belt it was so big," recalls deep-sea ecologist Christopher Bird, who was also aboard the ship.

It's unclear whether or not the shark survived, but Brit Finucci, a PhD candidate at Victoria University of Wellington who studies deep-sea sharks and their relatives, explains that it really depends on what state the animal was in. "Chances are, even if the shark was still alive at the time, it was probably on its way out," she says. "Not only do the animals have to cope with the trauma of being hauled up by net, but there's also significant environmental changes to adjust to, including pressure, temperature and light, as well as being taken out of water. It'd be quite a shock to the system. Simply throwing the animal back overboard while in this state may not increase its chance of survival."

That said, Bird assures us that the team did everything in their power to give the shark a fighting chance. "We quickly measured it, weighed it and took a few blurred pictures, but as the shark was still alive we wanted to get it back in the water as soon as possible. Everybody on board had a great passion for these sharks."

The measurements collected will provide important information that will help us better understand this little-known species. "It was such an amazing experience being able to witness this rare shark and once again proves how much we still don't know about the deep-sea!" says Bird.

For more information on the expedition check out the research blog!

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Top header image: NOAA Okeanos/Wikimedia Commons