Abstract

Two currently used methods for the long-term monitoring of marine mammals in conservation research are hot-iron branding and intra-abdominal transmitter implantation. These methods are thought to cause pain but there has been little research assessing pain responses in marine mammals. Animals may display immediate pain-related behaviors at the time of the procedure, or a delayed response in the days and weeks following due to tissue damage, inflammation and repair processes. Here we summarize the results of three recent behavioral studies describing acute pain responses in Steller sea lions after hot-iron branding (Study 1) and abdominal surgery required for the implantation of a telemetry device (Study 2 and 3). After hot-iron branding (under gas anaesthesia, no analgesia), sea lions spent more time grooming the branded area, less time with pressure on their branded side, less time in the pool and less time in locomotion for up to 72 h after branding. In the first post-surgical study, animals spent more time with their back arched and standing, and less time lying on the ventral side and in locomotion after abdominal surgery. Some of these behaviors persisted for the duration of the study (12 d). A subsequent study compared sea lions receiving a single dose of flunixin meglumine (IM injection of 1 mg/kg immediately prior to extubation from surgery) versus those receiving carprofen on multiple days (single IM injection of 4.4 mg/kg immediately prior to extubation from surgery, with subsequent oral doses for 3 d post-surgery). Animals on the carprofen protocol spent less time standing, more time alert, and more time lying down after surgery compared with sea lions that received a single dose of flunixin meglumine. These results suggest that repeated treatments with carprofen may be more effective than a single dose of flunixin meglumine in controlling pain following abdominal surgery, but neither approach eliminated the behavioural responses. Our results illustrate that post-operative behavioural responses can be useful in assessing pain in sea lions, and perhaps other pinnipeds, and suggest that variation in these responses can be used to compare efficacy of treatment protocols.