Fisheries officials off the coast of Taiwan have hauled up a gaggle of rare viper dogfish. The inky shark is known for its set of extendable glassy jaws, lined with crooked "nail-like" teeth. Sparse historical records make the recent find a real head-turner!

The details around the sighting still remain unclear, however, according to local reports, five specimens were caught during an offshore trawl near Donghe Township on the country's East coast. Most (if not all of them) were likely dead at the time they were found, but with any luck, they will be kept for scientific study. 

Viper dogfish (Trigonognathus kabeyai) are deep-sea dwellers: they have been found 360 metres (about 1000ft) below the surface, but it's possible that they may venture even deeper than this. Most previous catches have occurred at night, which likely indicates that the animals are vertical migrators who ascend to feed when the sun dips below the horizon, much like their cookiecutter-shark cousins. 

Contrary to some reports, this isn't the first time one of these poorly-studied sharks has been found in Taiwan. A 2012 biodiversity survey led by Pacific Shark Research Center program director Dr Dave Ebert turned up six specimens from the region's oceans and fish markets.  

Still, Ebert notes that the sharks are not commonly seen, and many aspects of their lives are yet to be illuminated. "They're only really known from a few specimens off Japan, Taiwan, and one from Hawaii," he says. "I suspect they may be caught a bit more, but unless someone knows what they are or is keenly interested in these 'lost sharks' they usually go unreported." 

In fact, the elusive creatures were only first discovered in 1986, and their official description came four years later.

The recent sighting has already stirred up several scaremongering headlines, but don't let the dogfish's menacing grin fool you: these sharks rarely exceed 47 centimetres (18 inches) nose-to-tail. 

Fisheries biologist Dr Brit Finucci - who studies deep-sea sharks, rays, and chimeras - suspects that this slight stature may contribute to infrequent encounters. 

"Smaller individuals may escape through mesh nets," she says. "Or they may inhabit parts of the ocean where there is little human interaction. They're on my wishlist of species to see!"

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Viper dogfish specimen discovered in Hawaii. To date, this record remains the only one of its kind for the area. Image: Wetherbee et al./Pacific Science

What's more, the untrained eye would have a tough time differentiating between a viper dogfish and other members of its lanternshark family. (Test your skills here!)

"It sort of reminds me of a lanternshark that has undergone some kind of diabolical experiment!" adds Ebert. "It is definitely a bizarre-looking shark!"

On paper, the viper dogfish is something of a biological mash-up, sporting features also seen in distantly related shark groups. The animal's snake-like head is reminiscent of the commonly encountered frilled shark, while those triangular "go-go-gadget-jaws," are similar to slingshot-feeders like the goblin shark. 

Scientists have yet to witness viper dogfish hunting behaviour, but it seems likely that they tuck in using a similar strategy to the goblin shark:

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Image: NHK

The spiky teeth of the dogfish are better suited to grasping rather than cutting and sheering, and some prey items (small fishes and crustaceans) recovered from dogfish bellies were swallowed whole.

With so few specimens available for study, it's tough to pin down these details with certainty, and more work is needed to determine viper-dogfish abundance, conservation status, and any potential threats. Each new individual that's found holds the potential for scientists to unravel another dogfish secret.

We've reached out to the trawling team for more information on the recent additions, so watch this space!

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Top header image: Dr David Ebert