A ray known for basking on the ocean surface has turned out to be one of the natural world's deepest divers, able to forage at submarine-crushing depths, scientists said this week.
Researchers attached data recorders to 15 Chilean devil rays (Latin name Mobula tarapacana) in the mid-Atlantic to see where the horned, kite-shaped fish went.
The recorders, which transmitted information via satellite, tracked the rays' movements for up to nine months.
Contrary to belief that the rays were languid surface-dwellers, the probe found they dived to extreme depths of up to 1,896 metres and in water temperatures of just 3.6 degrees Celsius.
"M. tarapacana is among the deepest diving ocean animals," declared the study, led by Simon Thorrold of the Woods Hole Oceanographic Institution in Massachusetts.
The deep-dive record for an air-breathing animal is held by a Cuvier's beaked whale, with a dive of 2,992m.
The deepest observed dive for a fish is 1,926m, by a whale shark - a massive animal compared to the devil ray, which grows to about three metres long and about 350 kilograms.
The investigators deduced the rays warm up on the surface and then use this reservoir of heat to sustain key bodily functions at chilly temperatures.
Part of the trick lies in their ability to descend at astounding speeds - a dizzying six metres per second, or 22 kilometres per hour.
The rays also turned out to be astonishing travellers, covering up to 49km per day.
Despite the discovery, many things remain unknown about the Chilean devil ray - what it feeds on, its reproductive cycle and its impact on deep-ocean ecology.
Large numbers are killed to supply growing demand for their gills in Asia for traditional medicine, or are taken accidentally as bycatch in tuna fishing.
The International Union for Conservation of Nature (IUCN) lists the Chilean devil ray - also called the box ray - as "data deficient" on its endangered species Red List.
The study was published in the journal Nature Communications.