Cameras On Sharks Show Their Deep-Sea Secrets

It's a first of its kind. Recently, scientists mounted cameras on the fins of deep-sea sharks, which revealed some surprising secrets on what kept these animals afloat.

While earlier, researchers felt that sharks were "negatively buoyant (meaning they have a natural tendency to sink) or neutrally buoyant (meaning their buoyancy is canceled out by their weight in the water", scientists have now discovered through their underwater cameras that sixgill and prickly sharks show a small amount of positive buoyancy that brings them to the surface, according to yahoo.

A small camera was attached by the scientists at the University of Hawaii and the University of Tokyo to the deep-sea sharks, at a depth of 6,500 feet (2,000 meters). The camera can be paired with a strobe providing light that could shoot images in the dark, deep waters. Click livescience here  to see photos of the deep-sea sharks with fin-mounted cameras.

"The flashlight-size camera captured images every 30 seconds while the sharks were swimming. When combined with data from the accelerometer and magnetometer, the scientists were able to figure out that the sharks had to work hard to dive down, but they could easily glide back toward the surface," according to livescience.

The system was put in place to study some of their deep sea secrets. "We set a date and time we want it to come off, the metal band breaks and drops off the shark and the package floats up to the surface of the ocean [and] sends us a satellite sign of where it is," said study co-author Carl Meyer, an assistant researcher at the University of Hawaii at Manoa's Hawaii Institute of Marine Biology.

The researchers found some very surprising results. "It was not at all what we expected to find," Meyer said. "Conventional wisdom suggests sharks are generally negatively buoyant---they'll sink if they stop swimming."

Even though they knew that sharks have some neutral buoyancy, they did not expect that sharks would actually float up.

At first, Meyer was puzzled and wondered if their equipment package was affecting the shark's buoyancy. However, after re-calibrating and repeating the experiment, the results stood firm, he said.

The data recorded by the accelerometer and the frequency of the sharks' tail movements showed that the energy of the sharks was used to muscle downward. "What we saw by comparing uphill and downhill movements, among all the individuals tested, the tail was working harder at any given speed than when they were going up," Meyer said. "When they were going uphill, they could glide for minutes at a time without beating their tails."

However, it would require a lot more effort to figure out why it benefits the sharks to be buoyant and how many species have this trait, according to the researchers.

Is positive buoyancy widespread among deep-sea organisms, Meyer wondered. "The deep sea is dark and cold, with low oxygen and limited food resources," he said. "There may be that something about being positively buoyant allows you to go down into very unfavorable locations, and still make it back up to where it's warmer."

Moving between ocean depths could help sharks digest and process their meals, Meyer added. "You go up to catch stuff, and then the colder area lets your digestion suck up the nutrient."

Meyer agreed that a lot more study is needed to find out more about the deep sea sharks: "Finding positive buoyancy in [deep-sea] sharks is demonstrative that we have a lot to learn about deep-sea animals and how they survive."

The detailed findings of the study were published June 10 in the journal PLOS ONE.