Scientists discover new giant fish species off Japan's coast

There is a great variety of sea life swimming in Earth's oceans, but according to the National Ocean Service, more than 90% of the species living in them are not yet classified. So when scientists stumbled onto a toothy deep-sea "top predator" off Japan's coast, they could not believe a fish of that size was swimming around the deep blue. Lucy Craft has more.

Video Transcript

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DANA JACOBSON: Welcome back to CBS This Morning, Saturday. We've all heard about the great variety of sea life swimming in our oceans. So the following stat may surprise you. According to the National Ocean Service, more than 90% of ocean species have yet to be classified. So it's quite an event when something brand new is brought to the surface, as recently happened in the waters off Japan. From Tokyo, Lucy Craft shows us what they found.

LUCY CRAFT: Back in 2016, an expedition off central Japan yielded an astonishing discovery. Specially made fishing lines long enough to reach the ocean floor ended up hooking a purplish monster.

JAN YDE POULSEN: This new species--

LUCY CRAFT: When Denmark-based biologist Jan Yde Poulsen saw the first image, he was skeptical.

JAN YDE POULSEN: It's a very grainy photo, almost like when you see a photo of the Loch Ness Monster or something, you kind of, what is this? There was no scale. And when they told me it was 25 kilos, I couldn't believe it.

LUCY CRAFT: The monster was identified by Japanese researchers as a slickhead, a fish named for its scale-free head. But most slickheads are only about a foot long. This creature was the size and weight of a small child.

Japanese scientists captured a rare glimpse of the fish in motion. A switch of its tail suggesting a fast, powerful swimmer.

It's kind of a mystery, that-- finding this fish was surprising, but it's also a mystery. How could something this large survive in an environment that's so hostile?

JAN YDE POULSEN: It's not surprising to find big, bony fishes in surface layers of the ocean. But down that death depth is a completely different story.

LUCY CRAFT: Isotope analysis proved the fish, dubbed yokozuna, or sumo champ, was an apex predator, the deep sea equivalent of a lion or killer whale.

For marine biologists, Japan's chance discovery in the forbidding underwater canyon of Suruga Bay, 8,000 feet below the surface of the ocean, underscores how our final frontier is right here on Earth.

JAN YDE POULSEN: There's a saying that we know much more about the moon than the deep sea, and it's very true. We know very little about the deep sea. It's very obvious. And this fish is a perfect example of that statement.

LUCY CRAFT: For CBS This Morning Saturday, Lucy Craft, Tokyo.

- I always thought that was so interesting, and such a great point, that we know so little about the bottom of the ocean. But no--

- Now we know about a lion.

- But who knew, 90%? We were that in the dark about it.

- Yeah.

- Unbelievable.