New non-invasive methods for short-term electronic tagging of pelagic sharks and rays

Biologging technology has provided scientists with unprecedented tools to investigate the ecology and behaviour of marine animals, but tag deployment and attachment methods have lagged behind. Electronic tagging of elasmobranchs still essentially involves implanting anchors or drilling the fins of restrained animals. Here, we present two new non-invasive methods for deploying satellite and biologging tags on pelagic sharks and rays that do not require restraining or manipulation of the animals, nor the attachment of intramuscular anchors. The attachment of a modified fin clamp and a harness systems were tested on 12 blue sharks and four devil rays in the Azores, mid-north Atlantic. Clamps and harnesses were fitted with galvanic timed releases and deployed manually by a free diver or from the boat using a harness tagging pole. The tags remained on the animals over the entire short-term duration of the trials. Focal observations and deployment data suggest that both methods produce little or no adverse behavioural reaction on the animals, offering a valid alternative for short-term tagging of pelagic sharks and rays. Deployment length can be substantially increased by selecting longer duration galvanic timed releases.