Devil Rays Dive 6,000 Feet to Feast
A group of Chilean devil rays swim together at the top of a seamount off the coast of the island of Santa Maria. Researchers have observed deep diving behavior in the species for the first time.
The National Oceanic and Atmospheric Administration (NOAA) is celebrating "30 Days of the Ocean" in the month of June, and in honor of the organization's hat-tip to life undersea, we take a look, this final June weekend, at some of the organization's captivating marine life snapshots. Here, the eyes of a queen conch (
) peek out from under its shell in La Parguera, Puerto Rico.PHOTOS: 30 Days of the Ocean
Robert Schwemmer, NOAA National Marine Sanctuaries
Kelp and sardines, just doing what they do, off Anacapa Island, Channel Islands National Marine Sanctuary.Whales Get Fishing Tips From Peers
This school of permits contains 60-80 individuals, each more than a foot long. The school was observed in the Dry Tortugas, Florida.PHOTOS: Shipwreck Hunt Turns Up 'Tar Lilies'
A Caribbean spiny lobster strolls on the sea floor. This photo was shot during a 2010 NOAA expedition in the U.S. Virgin Islands to map underwater habitats and the marine life they support.Deep-Sea Methane Ecosystem Found in Atlantic
DNA testing confirmed that the eggs pictured here were those of a loggerhead turtle, a marine reptile species listed as threatened under the Endangered Species Act. The testing was done by NOAA's Center for Coastal Environmental Health and Biomolecular Research, in Charleston, S.C., the only lab in the country dedicated to forensic analysis of marine species.PHOTOS: Sea Turtles From Shell to Surf
This manta ray coasts over a reef, in the process inviting much smaller fish to clean parasites and other debris off of it. Manta Rays are the largest type of ray in the ocean.The World's Biggest Manta Ray Sanctuary Created
Make way for the balloonfish, also known as a porcupine or spiny puffer fish. As its name suggests, it will swell up like a balloon when attacked.VIDEO: Flushed Fish Invading Oceans
Robert Schwemmer, NOAA National Marine Sanctuaries
Off the California coast, a group of elephant seals sleeps in the sun on a sand dune on Active Point, San Miguel Island, part of the Channel Islands National Marine Sanctuary.
With its distinctive reddish and white stripes, its gracefully flowing fins, and its menacing spine, not many fish can embody the beauty, mystery, and danger of the ocean quite like the lionfish. Although it's native to the Indo-Pacific region, lionfish were introduced to the Atlantic and are now found along the U.S. coast, from North Carolina to Florida, and in the Bahamas and Caribbean. The lionfish spells trouble for the balance of ecosystems and fisheries it invades, as it can out-compete native species for food and space. It lacks predators, has a voracious appetite, reproduces quicly, and is spreading fast.
The Chilean devil ray has always been considered a shallow-water swimmer, but new research shows that the species frequently dives to depths of more than 6,000 feet (1,800 meters), likely in search of food.
Prior to this research, marine biologists thought Chilean devil rays (Mobula tarapacana) did not descend below 3,280 feet (1,000 m). However, new satellite tracking data now shows that these rays are among the deepest-diving marine animals. Researchers think the rays spend most of their time in shallow water to warm themselves, and then dive down to extreme depths in search of small crustaceans and fish to eat.
"The fact that they were traveling so far horizontally was not necessarily surprising, but the diving behavior was very surprising," Simon Thorrold, a senior scientist at Woods Hole Oceanographic Institution in Woods Hole, Massachusetts, told Live Science. "What they're doing down there is the big unknown." [In Photos: The Wonders of the Deep Sea]
It's common for ocean predators to dive into the mesopelagic zone, a stretch of ocean water 656 to 3,280 feet (200 to 1,000 m) below the surface, to feast on squid and krill. But few predators make it deeper than the mesopelagic zone to the bathypelagic zone.
The bathypelagic zone is a huge food resource, home to an estimated 10 billion tons of prey fish, but few ocean predators can withstand the extreme pressure, cold temperatures and low oxygen levels.
In deep ocean zones, the water can be as cold as 37 degrees Fahrenheit (3 degrees Celsius). Deep-diving ocean predators must maintain a higher brain temperature than the surrounding water, so they are equipped with a special organ called the rete mirabile. The organ functions as a heat-exchange system that warms the animal's brain and helps it function better in the extreme cold. The organ also helps the animal see better when it's hunting in deep, dark waters.
Scientists were puzzled as to why Chilean devil rays, believed to be surface dwellers, had the organ. Researchers originally suggested that the rete mirabile helped to cool the brains of the rays living in the warm and shallow tropical waters.
A group of Chilean devil rays swim together at the top of a seamount off the coast of the island of Santa Maria. Researchers have observed deep diving behavior in the species for the first time.Nuno Sá
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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