Perhaps you've seen footage from National Geographic's "Crittercam," an underwater video camera that has been attached to animals such as sharks and whales. Well, scientists from the University of Hawaiʻi at Mānoa and the University of Tokyo have gone one better. Not only have they been putting cameras on sharks to see what they get up to, but they've also been slipping them ingestible sensors, to monitor their dietary habits. The data that they've gathered could help protect shark populations, and the overall health of the ocean.
The video camera packages also include an accelerometer, a data-logging computer, and a VHF transmitter. They're strapped onto the pectoral fins of sharks that are caught and released by the researchers, and they then proceed to record footage from the sharks' point of view as they travel through the sea. The packs automatically release themselves from the fish after a set amount of time, at which point they float to the surface to be located and retrieved via their radio signal.
The "feeder tags," on the other hand, are fed to the sharks. Once in the digestive tract, they measure electrical signals to track the ingestion and digestion of prey. Combined with the images and other data from the camera packs, they also provide a record of what animals the sharks have been eating, along with where and in what quantities.
Carl Meyer, a scientist at the University of Hawaiʻi who is one of the project leaders, told us that the tags have so far been tested on captive sharks at the university's Hawaii Institute of Marine Biology. "Sharks naturally regurgitate indigestible material, so we take advantage of this natural phenomenon to recover the tags (we find them floating in our shark enclosure)," he explained. "We have already field tested a satellite tag version with wild sharks. The regurgitated tags successfully transmitted their locations to satellite. In future we will be using the satellite tag version to measure feeding in wild sharks, and using the satellite fix to physically recover the tag for downloading."
Although the research is still in its early stages, the technology has already allowed the team to learn that sharks move by powered swimming more than by gliding (the opposite was previously thought), and that deep-sea sharks swim much slower than other species.
"These instrument packages are like flight data recorders for sharks," said Meyer. "It is all about getting a much deeper understanding of sharks’ ecological role in the ocean, which is important to the health of the ocean and, by extension, to our own well-being."
You can see footage from some of the camera packs in the video below.
Source: University of Hawaiʻi
