For the ultimate shark’s eye view, researchers strapped cameras onto the fins of over 30 sharks and watched them as they swam and feasted freely off the coast of Hawaii.
Being at the top of the food chain, sharks play a huge role in ocean health, and knowing more about them helps scientists understand the flow of energy through the ocean, according to study researcher Carl Meyer of the University of Hawaii at Mānoa.
Here’s the shark count, from the Los Angeles Times: 14 tiger sharks, six Galapagos sharks, five sandbar sharks, five bluntnose sixgill sharks, and a prickly shark.
Together with University of Tokyo researchers, the team outfitted sharks with sensors and video recorders -- specifically, accelerometer-magnetometer data loggers for information about position, along with miniature video loggers. They’re like little flight data recorders, Meyer explains, but for sharks. A VHF transmitter helps them track down the devices after they detach and float to the surface.
The footage revealed how sharks of different species swim in schools, interacting with other fish. “We had no idea that these mixed-species aggregations existed,” Meyer tells the LA Times, “even though it’s just a few miles offshore.” They think they travel in those groups for protection against larger sharks. In one camera, for instance, a sandbar shark steadily swam upward to join a mixed school of sandbar sharks, oceanic blacktips, and scalloped hammerheads, National Geographic details. And as Meyer describes it, the whole motley crew "spiraled up like a shark tornado.”
Another surprising thing they found: The sharks used powered swimming more often than a gliding motion, contrary to what we previously believed. And as it turns out, deep-sea sharks swim in slow motion, compared to shallow water species.
If you noticed how the sharks are belly-up, that’s because in order to mount the devices onto pectoral fins, the team relied on “tonic immobility.” As the LA Times explains: Flip a shark over onto its back, and it suddenly goes into a calm, trance-like state.
In a related study, sharks and other top predators, like tuna, were actually given instruments to ingest. Using electrical measurements to track their various phases of ingestion and digestion of prey helps researchers better understand their feeding habits -- answering questions like what, where, when, and how much top predators eat.
Previous studies that have tried to answer these sorts of basic questions have relied on observing the animals in captivity and on satellite tags with coarse data.
The work (abstracts here and here) were presented at the 2014 Ocean Sciences Meeting in Honolulu last week.
Image: Mark Royer/University of Hawaii
Video: University of Hawaii/University of Tokyo and Mark Royer/University of Hawaii