Underwater shark surveillance drones are good for a lot more than viral videos of great whites. As it turns out, Woods Hole Oceanographic Institute's REMUS SharkCam autonomous underwater vehicle (AUV), deployed in 2013, has enabled research the team called "groundbreaking." Their paper has been published in the Journal of Fish Biology.
"We wanted to test the REMUS SharkCam technology to prove that is was a viable tool for observing marine animals -- sharks in this case -- and to collect substantial data about the animals' behaviour and habitat," said WHOI engineer and one of the principal investigators Amy Kukulya.
During six dives over a period of a week in November of 2013, the AUV tagged four great white sharks and collected 13 hours of video data off the coast of Guadalupe Island in Mexico. The idea was to track the sharks, then send the AUV down after them to observe what they were doing underwater. Most data on shark behaviour has been collated from surface observations, so this was something of a coup.
"We wanted to find out what was happening at depth -- when the sharks swam into the deep, how were these animals behaving? Were they hunting? The REMUS AUV was the perfect tool to do this," explained lead author Greg Skomal.
Using the SharkCam, the team was able to record the first observations of shark predatory behaviour made in the ocean's depths.
The robot had 30 interactions with 10 sharks (the four tagged sharks and six more that just showed up for the party). Sometimes they would simply approach and bump the AUV, usually with their noses, behaviour that the team interpreted as aggressive. On nine occasions, including the famous incident with Deep Blue, the sharks bit the AUV, usually in the rear. This behaviour, the team interpreted as predatory.
The team's findings suggest that the sharks move hidden through the darker depths, using the clearer waters towards the surface to their advantage. When they spot prey, such as a seal, swimming above, cleanly outlined against the sky, they ambush from below.
The team's research continues, with a return to Guadalupe Island last month. They use a harpoon to tag the dorsal fin with a transponder that allows the SharkCam to follow them to a depth of around 100 metres. The AUV, which is equipped with water current sensors, temperature and salinity probes and other sensors, is able to send back a profile of the environment, while the high-definition cameras observe the sharks. When the team has finished with their observations, they send a command to the AUV, which releases the transponder from the shark's fin.
"There is currently no other method in the world that can get imagery of white sharks at depth in the open ocean. Not only do we get to see what they are doing, but we also know exactly where they are and collect data about the physical environmental in which they live," Kukulya said.
Footage from the most recent expedition will be released for Discovery's 2016 Shark Week.