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Tonic immobility is a widely used technique for the surgical implantation of acoustic tags in elasmobranchs (sharks, skates, and rays), yet it is still not broadly recognised as an acceptable procedure by many regulatory bodies, animal care committees, and even journal ethics standards. To highlight its regular use and applicability as a field procedure, a literature search was conducted on the anaesthetic technique adopted for all existing elasmobranch-focused acoustic telemetry papers, up to 31 December 2013. A total of 57 studies were identified that contained relevant details on surgical methodological procedures. Of these, the majority of studies (43, or 75.4%) employed tonic immobility, while 10 (17.6%) used general chemical anaesthetic and 4 (7%) used local chemical anaesthetic. These studies identify that tonic immobility provides an effective anaesthetic for surgical implantation in elasmobranchs, as it offers several benefits over chemical anaesthetics, both from a practical and from an animal welfare perspective. Practically, rapid induction and recovery optimizes the surgical procedure, desirable under often complex field conditions, where general chemical anaesthetics prolong duration and administration is often unfeasible because of the size of study animals. Benefits over chemical anaesthetic for animal welfare include no risk of overdose, no uptake of chemicals to body tissues, minimal disruption to respiration, thereby reducing potential for negative sublethal impacts that influence postrelease behaviour, and immediate and full recovery. Given these benefits and its long-standing use in field studies, it is recommended that tonic immobility be recognised as an acceptable anaesthetic technique for surgical procedures on elasmobranchs.
Kessel et al. (Wed,) studied this question.