Aquatic drones used to track whale shark movements

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Aquatic drones used to track whale shark movements

January 27, 2017 - 03:05
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Technology able to obtain depth and positions in real-time

Whale Shark

For the first time, wave-powered drones have been used to provide live tracking of whale sharks. Researchers at the Whale Shark and Oceanic Research Center (WSORC) on the island of Utila, Honduras, have just finished a year-long project using autonomous “Wave Glider” drones to patrol for whale sharks and report back on their movements. The team could follow individual sharks in real-time as the drones relayed the depth and minute-by-minute positions. They discovered whale sharks feeding off the Utila coast at unexpected times of year, illustrating the potential for the technology to fill significant gaps in our understanding about the endangered species.

In July, drones spotted one individual at a depth of 90m, a time when it was believed the sharks had migrated north toward Mexico. “With the turbulent weather during these months, it’s difficult to find whale sharks feeding as rough waters prevent the plankton, roe and coral spore they feed on from settling at the surface,” according to Konrad Madej, former research director at WSORC and lead researcher on the project. “So, it’s great to see they’re still swimming at depth for the first time via the Wave Glider,” he added.

Difficult to track

As mature whale sharks can dive to depths of 1.5 kilometres and swim 10,000 kilometres a year, locating and following them is difficult. “Just being able to track them over longer periods while sampling oceanographic data would improve our insight into which habitats they use, why and what threats they might be particularly susceptible to,” says Simon Pierce, principal scientist at the Marine Megafauna Foundation.

To obtain data, the project utilized Wave Glider SV3 drones built by California-based Liquid Robotics. Able to operate uninterrupted for up to 12 months at a time, the drones employ wave energy to propel themselves. A surface float incorporating solar panels, sensor equipment and transmitters is attached to a finned sub-unit below the surface. The sub’s fins pivot up and down as the waves lift the float and drive it forward at up to 3 knots (5.5 kilometres per hour).

The team set the drones to patrol 5 kilometres off Utila’s north shore where whale sharks are commonly observed. Each drone towed a receiver unit able to pick up signals from any shark with an acoustic tag. The tags can be fitted to a whale shark’s dorsal fin and release a sonic pulse every 60 seconds. Not only are they cheaper than more sophisticated satellite tags, they can better handle the pressure as the sharks dive.

Although Pierce said there is still some way to go to live-monitor whale sharks – the longest continuous tracking was 25 minutes – but he is “hugely interested” in the findings of the initial studies.

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