Researchers tagged 15 Chilean devil rays off the coast of northern Africa and tracked them for nine months. The satellite data revealed that the rays can reach depths of around 6,560 feet (2,000 m), where temperatures can drop as low as 37 degrees Fahrenheit.
The rays typically hover just a few feet below the surface for about an hour, before descending deep into the cold water. Most of the dives followed the same pattern. The rays would first dive to the maximum depth, and then ascend slowly in a stair-step pattern. The researchers think this stair-step pattern allows the rays to hunt for prey that usually travel in layered clumps in the bathypelagic zone. The dives lasted between 60 and 90 minutes, and the rays usually only made one dive in a 24-hour period.
Thorrold and the researchers think the devil rays likely dive for food, because the rays exhibit the same quick-descent and slower-ascent diving behavior that other ocean predators (such as sharks) use when hunting. However, more research is needed to confirm this idea, the researchers said.
Most of the dives happened during the day. This is likely because the rays can warm up more during the day and because prey are easier to catch during the day, when they travel in clumps, rather than at night, when they are more spread out, Thorrold said.
This is the only species of Mobula rays that researchers have observed diving. The scientists hope that more research into these marine creatures' behavior will reveal insights about the relationship between marine animals and different ocean zones.
The details of the discovery are published today (July 1) in the journal Nature Communications.
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