The researchers made the discovery while exploring the Davidson Seamount with an underwater submersible vehicle.
"We went down the eastern flank of this small hill, and that's when – boom – we just started seeing pockets of dozens here, dozens there, dozens everywhere," the Nautilus' chief scientist, Chad King, told National Geographic.
The Davidson Seamount is a gigantic undersea volcanic mountain off California's coast that measures 26 miles long and eight miles wide and is one of the largest known seamounts in U.S. waters. The underwater mountain is 7,480 feet tall, but its summit is still 4,101 feet below the ocean surface, according to the sanctuary. It's a pristine habitat for many sea creatures and therefore of interest to scientists studying the region.
The crew, which livestreams many of its adventures, also recorded a rare, dumbo octopus, also known as an umbrella octopus, cruising through the deep, with its ear-like fins flapping in true Dumbo fashion.