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What Is a Sofa Shark?

One was caught off the coast of Scotland. What the heck.
September 30, 2015, 4:50pm

Rare "sofa shark" found off Hebrides
— Scotsman (@TheScotsman) September 30, 2015

Of all the animal families (okay, technically "classes"), it is perhaps the sharks that are given the very best names. Where else will you find names as spectacularly weird as the Birdbeak Dogfish, the Tasselled Wobbegong, or the Bowmouth Guitarfish?

One of these excellently-named creatures, the False Catshark, was recently caught off the waters of Scotland, which gives us license to talk about how bizarre this fish is: we're talking a 50-pound oily liver, hundreds of teeth, eggs that suck yolk from other eggs, and a body soft enough that the animal is sometimes casually referred to as a "sofa shark."

So! The False Catshark is a ground shark, placing it in the same general category as much better-known sharks like the Hammerhead. Also in that category are the Catsharks, so named for the surprisingly pretty, cat-like shape of their eyes. Catsharks are very common and not very weird-looking; the False Catshark was so named because a Portuguese shark scientist, Félix de Brito Capelo, found one and thought it looked kind of like a catshark. But, he reasoned, this weird blobby shark couldn't be a true catshark, because it lacks a nictitating membrane, a protective, clear eyelid that lays on top of the eye. So he named it a False Catshark.

"…a sort of egg cannibalism in which the stronger eggs feed on the weaker eggs"

Capelo was wrong; the False Catshark does in fact have a nictitating membrane. But he was also right in that it is related to, but not a member of, the catshark family. Sometimes when you're wrong you're actually right!

Anyway. The False Catshark, typically dark brown (though sometimes light grey), is a pretty big shark, at its largest nearly 10 feet long and 275 pounds in weight. But a significant portion of that weight, up to 25 percent, is in its liver, an enormous organ filled with super gross shark liver oil. That liver helps the shark stay buoyant and float where it wants to be, just off the sandy sea floor, where it chomps down with its enormous, 200-toothed mouth on bony fishes and shrimp. Oh and also, like, whatever else it finds; a 1992 study of False Catshark stomach contents found that it'll also eat human garbage, "including potatoes, a pear, a plastic bag, and a soft drink can in one Atlantic specimen." Haha, soft drink cans! It's like a sea-goat.

Another very weird thing about the False Catshark: it reproduces with a method called intrauterine oophagy, a sort of egg cannibalism in which the stronger eggs feed on the weaker eggs, replenishing their yolk sacs by murdering other baby sharks. No other ground sharks do this, and in fact very few animals in general do it.

The False Catshark typically is found in fairly deep waters, between 1,600 and 4,600 feet, which explains its soft, flabby, blogger-like body. Deep-water fish often have very sort of gelatinous, blob-like bodies, which allow them to cope with the extreme pressures of the deep ocean. What makes the False Catshark weird is that it isn't always found in the deep ocean; it's been known to crawl up to pretty shallow waters, like off the coast of Scotland, where this latest specimen was caught.

Speaking of distribution! Not all that much is known about the False Catshark; the IUCN Red List, which decides whether species are endangered or not, lists the False Catshark as "data deficient," which means, you know, shrug? It's been found in as varied places as off the coasts of Canada, Cuba, Madagascar, Japan, and France, places with wildly variable water temperatures, depths, and possible prey.

It would be very difficult to go out and attempt to catch a False Catshark, given how little we know about its habitats and population. It is occasionally caught by accident in deep-sea trawls, but it's generally thrown back; nobody seems to much want to eat a squooshy, incredibly ugly giant shark, though one source suggests its abundant liver oil has been used to seal ship hulls in Okinawa.

So there's your intro to the False Catshark, truly one of the weirdest and ugliest fish on the planet, at least that we know about. You're welcome!