Short-term effects of standard procedures associated with surgical transmitter implantation on a benthic shark species requiring anaesthesia

Abstract

Surgical implantation of acoustic transmitters is a widely used method to study the movement ecology and eco-physiology of sharks. Nevertheless, the impact of surgical implantation on the behaviour of the target species is seldom separated from the capture stress. Pyjama catsharks (Poroderma africanum) is a small benthic shark species endemic to South Africa. For this species, tonic immobility is insufficient to achieve adequate sedation for surgical implantation of internal transmitters and a combination of tonic immobility and anaesthetic is needed. Therefore, behavioural responses to surgical implantation of internal transmitters were quantified in pyjama catsharks using tri-axial accelerometers in a controlled captive environment for a 24-h period after capture and a 24-h period after surgery. A 2-state hidden Markov model was developed to investigate the sharks’ activity patterns, as well as the related possible effects of the treatment type (capture vs surgery and surgery vs non surgery) and time of day. The results showed that the sharks which went through surgery (treatment group) spent significantly more time (58.7 % of their time) in a lower activity state, which we believe relates to higher stress levels, following surgery compared to following capture. Furthermore, sharks in the treatment group spent roughly 20 % more time in the lower activity state compared to the control group (without surgical implantation). These results could be related to the sedating effect of the anaesthetic, and/or suggest short-term behavioural stress response to the surgical implantation of transmitter, related to either biochemical stress or anatomical discomfort. Furthermore, the sharks changed their behavioural state more frequently in the three hours after the surgery and spent more time in a lower activity state. This emphasises the importance of allowing the sharks enough time to recover from the combination of anaesthesia and surgery before being released into the ocean.