Development of single-pin, un-barbed, pole-tagging of free-swimming dolphins and sharks with satellite-linked transmitters

Abstract

Abstract Background To tag large marine vertebrates, without the need to catch them, avoiding using barbs for tag retention, and precisely controlling tag location, the remote Tag Attachment Device on a pole (TADpole) was developed. This allows single-pin tags (Finmount, Wildlife Computers) to be attached to the dorsal fins of free-swimming large marine vertebrates. Results TADpole comprises a pole-mounted holster that carries a tag. It uses compressed air, and a micro-controller, to rapidly insert a stainless-steel pin through a corrodible metal retaining ring in the first tag attachment wing, the animal’s dorsal fin, and then a press fit Delrin retaining ring in the tag wing on the other side of the fin. Tagging only occurs when the trailing edge of the dorsal fin touches a trigger bar in the holster, ensuring optimal pin placement. It was developed using fins from cadavers, then trialed on briefly restrained coastal dolphins that could be followed in successive days and weeks, and then on free-swimming animals in the field. The latter showed very short touch/response intervals and highlighted the need for several iterative revisions of the pneumatic system. This resulted in reducing the total time from triggering to tag application to ~ 20 ms. Subsequent efforts expanded the TADpole’s applicability to sharks. One free-swimming Atlantic spotted dolphin, two white sharks, and one whale shark were then tagged using the TADpole. Conclusions Being able to tag free-swimming dolphins and sharks remotely and precisely with satellite-linked telemetry devices may contribute to solving conservation challenges. Sharks were easier to tag than dolphins. Dolphin touch-to-response times were 28 ms or less. Delphinid skin has unique polymodal axon bundles that project into the epidermis, perhaps a factor in their uniquely fast response, which is 10 × faster than humans. Their primary reaction to tagging is to abduct the flippers and roll the fin out of the TADpole holster. This device has the potential to deliver high-quality tag data from large vertebrates with dorsal fins without the stress and logistics associated with catch-and-release, and without the trauma of tags that use barbs for retention. It also collects a dorsal fin biopsy core.