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In the summer of 2015,as eroticism revels in the scientists lowered a deep-sea exploration robot down 5,800 feet to the ocean floor off the Galapagos Islands. The pitch black world here is mysterious, so scientists expected to discover things never before seen.

"Every time we go to these depths we find something really unique," Pelayo Salinas, a senior marine biologist at the Charles Darwin Research Center on the Galapagos Islands, said in an interview.

During this particular dive, their remote-operated underwater robot, or ROV, came across 157 yellowish eggs scattered around the ocean floor near two extremely active undersea vents. These vents were spewing heated black, particle-rich plumes that are especially rich in sulfide minerals out into the water column.

The scientists found that the yellow eggs belonged to skates -- flat fish that look similar to stingrays -- and it appears the skates may have been incubating their eggs in the warmer waters near the vents, known as "black smokers."

"The positions of the eggs was not random," explained Salinas, who was a co-author on the study published today in Scientific Reports. "So we hypothesize that they actively seek these areas."

To Salinas' knowledge, this is the first time marine creatures have ever been seen using volcanic activity -- as the vents are fueled by molten rock beneath the ocean floor -- to incubate eggs.

Finding that skates look to be warming their eggs near black smokers is a wild illustration of what lies in the little-explored ocean depths that we still know little about, and suggests the ocean floor is rich in species employing unique survival adaptations.

The team believes the skates left the eggs in the heated water to hasten the eggs' embryonic development. Nearly nine in 10 eggs were found in hotter than average water. As it is, deep-sea skates' eggs can incubate for years, including an observed 1,300 days in Alaskan waters.

Such a unique incubation method is profoundly rare on either land or at sea; there's a Polynesian bird that lays its eggs inside volcanically-heated ground and a species of dinosaur that is suspected to have done something similar, millions of years ago.

Salinas and his team counted 157 skate eggs near the black smokers, 91 of which were found within 65 feet (20 meters) of the vents. All the eggs were located within about 500 feet of the smokers.

Curiously, Salinas noted that during eight other 24-hour dives with the ROV, the team didn't spot a single other skate egg in the depths they explored. The black smokers lie within the Galapagos Marine Reserve, which was expanded by 15,000 acres, an area the size of Belgium, in 2016.

Samuel Gruber, a marine biologist who has spent decades studying shark behavior -- and notes he's more of shark expert than a skate expert -- told Mashable over email that he had "never heard of [skates] placing eggs near a black smoker, or white smoker for that matter." Gruber was not part of the new study.

Gruber said it's possible the skates just happened to have dropped their eggs near the smokers by chance. Or, he mused that the skates could have indeed left the eggs near the nutrient-spewing vents "because there would be a potent source of food for the young once they hatch."

There's only one way to find out more about this curious -- and possibly intentional -- skate behavior, which is to send more exploration robots a mile or more down to the ocean floor. Salinas acknowledges these endeavors are pricey, but wants to better understand the mostly inaccessible, almost alien features of our own planet.

"We have a huge and deep ocean that we've hardly explored," he said. "We know more about the surface of the Moon or Mars than the ocean."