Chilean devil rays spotted off Cape Cod in aerial survey

Surveyors flying for the New England Aquarium counted more than 2,000 animals from 15 marine species in the Northeast Canyons and Seamounts Marine National Monument, which lies southeast of Cape Cod, as summer drew to a close, Popular Science reports. Among them were Chilean devil rays, a fish the aquarium calls "one of the ocean's best-kept secrets."

A rare sighting from the air

"We rarely see Chilean devil rays on our aerial surveys," Katherine McKenna, a researcher at the Anderson Cabot Center for Ocean Life, part of the New England Aquarium, told Popular Science. She was one of the observers who spotted the rays from the air.

McKenna linked the summer gathering to the monument's underwater landscape. "The Monument's deep sea canyons, complex oceanographic conditions, and productive waters support a remarkable diversity of marine life, especially in the summer months when warm water protruding from the Gulf Stream draws in seasonal visitors like Chilean devil rays," she told Popular Science.

The count is one survey, from the air, over one monument in one season. It is not a population estimate for a species spread across the tropics and warm temperate seas.

What the ray is

The rays also go by sicklefin devil rays. They are olive green or brown, with wingspans of 11 to 12.5 feet and weights of 715 to 1,100 pounds, which puts the heaviest at just over half a ton.

The common name comes from Chile, where scientists first documented the species. McKenna said the "devil" part comes from the horn-shaped fins, called cephalic fins, around the ray's mouth.

The IUCN Red List classifies the species as Critically Endangered. By-catch and overfishing are the main threats.

Hard to find, hard to study

Chilean devil rays are difficult to study. They roam long distances, are often solitary, and tend to stay far offshore. When they do gather, the group is called a "fever."

They are also the deepest-diving ray species, reaching depths of almost 6,000 feet, more than a mile down. "This is possible due to a specialized network of blood vessels surrounding their brain that allows them to keep their brain warm even at very cold water temperatures at deep depths," McKenna told Popular Science.

For a species that is usually solitary and often far offshore, a sighting from the air is a rare look at where it turns up in summer.

• Chilean devil rays
• IUCN Red List
• marine life
• New England Aquarium
• Northeast Canyons and Seamounts