Extraordinary footage of a rarely seen giant deep sea fish has been captured by scientists.
Using a remotely operated vehicle, they caught a rare glimpse of the huge oarfish, perhaps the first sighting of the fish in its natural setting.
The oarfish, which can reach 17m long, has previously only been seen on a few occasions dying at the sea surface, or dead washed ashore.
The scientists also filmed for the first time the behaviour of a manefish.
Mark Benfield from Louisiana State University, Baton Rouge, US was undertaking a survey as part of the Serpent project, a collaboration between marine scientists and energy companies such as BP, Shell, Chevron and Petrobras working in the Gulf of Mexico.
Using remotely operated vehicles (ROV) provided by the oil and gas companies, the scientists are able to explore the deep like never before.
During one of these surveys, the scientists glimpsed a giant oarfish.
Oarfish (Regalecus glesne) are one of the world’s longest fish reaching 17m.
Their strange appearance may have provided the basis for the sea serpent myths told by early ocean travellers.
Not only are they elongated, they also have a prominent dorsal fin which gives it an unusual “serpent” appearance.
Recalling the event Professor Benfield explained how at first, they thought the fish was simply a drilling pipe called a riser being lowered into the water.
“We saw this bright vertical shiny thing, I said ‘are they lowering more riser?’ as it looked like they were lowering a huge pipe.”
“We zoomed in a little bit and we said ‘that’s not a riser that’s a fish!'”
“As we approached it retreated downwards swimming tail first in a vertical orientation as the ROV followed,” Professor Benfield explained.
The team followed the fish for about five minutes before breaking off contact to resume their surveys.
“What was interesting about the fish was its swimming behaviour,” said Professor Benfield.
“It moved by undulating its dorsal fin in waves that propelled it backwards at quite a good speed.”
Early estimates measure the fish at between 5m and 10m in length.
Professor Benfield said this may be the first time the oarfish has been filmed alive swimming in the so-called mesoplagic layer of the ocean.
Usually, they are seen dying at the sea surface or washed up dead.
The fish may have been caught on camera at a depth of 765m at another Serpent survey site, off western Africa in 2007, but a positive identification has not yet been made from that video.
On this occasion the fish was observed underneath Thunderhorse in the Gulf of Mexico, one of the largest semi-submersible oil rigs in the world.
The Serpent project run by the National Oceanography Centre, Southampton (NOCS) is a unique collaborative project between scientists and industry. …
Below is the only known video of a live oarfish that came to the surface. See the BBC link for the video of the live oarfish filmed in the deep.