Abstract

Field research conducted in McMurdo Sound during the spring and summer (October through December) of 2006 and 2007 required repeated immobilization of adult male and female Weddell seals (Leptonychotes weddellii) for blood and tissue sampling, temporary placement of indwelling intravenous catheters and attachment and retrieval of data loggers and tracking devices. Combinations of a dissociative agent (ketamine hydrochloride) and a benzodiazepam (diazepam and/or midazolam) were utilized in 50 animals for a total of 72 procedures lasting up to 210 minutes. Seals were approached while hauled out on the ice, restrained with a head bag and injected intramuscularly by hand syringe into the caudal gluteal musculature. The induction dosage was calculated from an estimate of body mass made by experienced biologists based on size and body condition and confirmed by weighing each animal after immobilization. Depth of sedation, respiratory and heart rate, and body temperature were monitored along with time to immobilization, responses to procedures and rate of recovery. Local anesthesia (lidocaine HCl 2%) was injected subcutaneously to facilitate muscle biopsies. Additional increments of the immobilizing drugs were given intravenously as needed to prolong sedation for extended procedures. Decreased respiratory rate was the most common undesirable effect but was mitigated in response to intravenous injection of doxepram. Flumazenil and yohimbine were given to some animals to speed recovery with variable results. Oxygen supplementation was provided to 2 seals that experienced partial respiratory blockage (by nasal exudate in one case and an overly tight head bag in the second).

In 2006, midazolam appeared to provide a more consistent level and duration of immobilization as compared to diazepam when these drugs were given in combination with ketamine for intramuscular induction or when given intravenously, whether singly or in combination with ketamine, for maintenance. During the 2007 season, an intramuscular dose of 1.1 to 2.4 mg/ kg ketamine combined with 0.08 to 0.13 mg/kg of midazolam was used for induction on all animals. Sedation was reliably maintained using 0.11 to 0.55 mg/kg of ketamine combined with 0.005 to 0.03 mg/kg of midazolam intravenously at 5 to 25 minute intervals. Although there appeared to be significant variation in the response between animals, and even with repeated immobilization of the same animal at different times, adequate and safe immobilization was produced in all cases. Most doses were significantly lower than comparable recommendations for ketamine/diazepam combinations previously published for phocids.