On a sunny winter day in 2016, marine biologist Yoshihiro Fujiwara was anchored off the coast of central Japan, measuring plump cusk eels, when suddenly a commotion erupted aboard the ship. The crew of the Shonan Maru had just landed a large, bizarre-looking fish.
“Wow! We have a coelacanth!” they joked as they retrieved a specimen so large it evoked the legendary “living fossil” species found only in Africa and Indonesia.
JAMSTEC
Fujiwara, whose specialty is “whale trap” communities – the rich ecosystems that arise around and feed on whale carcasses – was as excited as it was skeptical.
“It was exciting,” he told CBS News. “But this is a very well-studied bay.”
Indeed. Researchers have been building a taxonomy of specimens from Suruga, Japan’s deepest bay, since the 19th century.
The area is also one of the most heavily exploited in the world. Certainly, Fujiwara thought, someone had seen this colossal creature before.
Amazingly, no one had. Fujiwara and his team from the Japan Agency for Marine-Earth Science and Technology (JAMSTEC) checked reference books and consulted with colleagues around the world before concluding that the spear-shaped, purple-hued creature of the deep was indeed a bona fide discovery.
Three more specimens of the monster fish would be hooked that year, quickly stored in formaldehyde, or frozen for later use in the lab.
JAMSTEC
On dissection, CT scans, and other analyzes, the sample was placed in the alepocephalid family, a deep-sea species that is distributed worldwide and popularly known as “slickheads” because of their shell-free heads and gill covers. But unlike its much smaller relatives, who averaged just 14 inches tall, this was an animal: At 55 inches tall and 55 pounds, it was the size and weight of a small child.
Fujiwara and his team decided to name the new strain “yokozuna slickhead”, after the highest rank in sumo wrestling.
“I couldn’t believe it,” biologist Jan Yde Poulsen, a research associate at the Australian Museum and an authority on slickheads, told CBS News from his base in Denmark.
Poulsen, who wrote a paper on the Yokozuna Slickhead with the JAMSTEC team in January, was also doubtful when he received the team’s first photo from Fujiwara.
“It’s a very grainy picture, almost like when you see a picture of the Loch Ness Monster,” he said. “The fact that you find a new strain that weighs 25 kilos is just unbelievable.”
Despite its hostile deep-sea, pitch-black habitat, the slickhead was not only large, it was also muscular. While other slickhead species gobble up plankton and weak swimmers like jellyfish, DNA testing of the giant fish’s stomach contents showed it was hunting other fish, perhaps supplementing its diet by scavenging.
Unlike the other 100 slickhead species known to the world, the yokozuna is a powerful swimmer, possibly able to travel long distances, as evidenced by a few seconds of rare video captured with a camera with bait at a depth of nearly 8,500 feet.
JAMSTEC
The slickhead’s “wide gaping” mouth houses multiple rows of teeth, evoking an alien monster. Fujiwara’s team tried to count the densely packed teeth and their strictly unofficial conclusion: “80 to 100” teeth in those jaws.
Its physical characteristics, in addition to biochemical analysis, identified the yokozuna slickhead as an apex predator – the deep-sea version of a lion or killer whale.
“We have so many dives around the world,” said Fujiwara. “But it’s rare to see an apex predator.”
The well-endowed maritime agency owns a slew of advanced underwater vehicles and other deep-sea reconnaissance vehicles, “but these are very noisy and use bright light,” Fujiwara said. “Most of the apex predators are very active, so (they) can easily escape our submarine.”
His team decided that deploying purpose-built long lines – long enough to reach the ocean floor, equipped with hundreds of mackerel hooks – would be more effective, albeit time consuming. It takes up to four hours to deploy these ultra-long lines, which remain in the water overnight.
Although hundreds of new fish species are identified every year, the inaccessible deep sea still holds many mysteries.
“We have no idea what’s down there,” said Fujiwara.