A new prospect for tagging large free-swimming sharks with motion-sensitive data-loggers

Sensor types in animal-attached tags (e.g. accelerometers, speed sensors and compasses) now often require devices to be solidly attached to an animals’ body, which would preclude their use on many large species of shark where current attachment systems are based on tethers. A new method of attaching motion-sensitive tags securely to large sharks is presented which allows free-swimming animals to be equipped without any form of restraint. The system was tested on 11 free-swimming whale sharks (Rhincodon typus) at Ningaloo Reef, Western Australia. Devices were placed on one of two elongated arms emanating from a torsion spring which acted to force the arms together. The system was clamped to the second dorsal fin using a specially designed tagging-gun operated manually by a snorkeller. Each arm was equipped with two 1.5 cm-long spikes to ensure stable, firm attachment to the fin. Data from the deployments showed that response to the tagging event varied between individuals, with some sharks showing no obvious reaction, while others exhibited a substantial reaction. Clamps remained stable on the sharks throughout the entire duration of all trials. The whole system was fitted with a corroding magnesium link to ensure that the clamp would release from the shark within weeks of deployment.