Immobilisation of free-living Weddell seals Leptonychotes weddellii using midazolam and isoflurane

Eleven lactating female Weddell seals were immobilised using inhaled isoflurane and oxygen, having initially been sedated using an intramuscular injection of midazolam. The seals were selected from colonies in Long Fjord, East Antarctica. Isoflurane was delivered using a precision, out-of-circle vaporiser in a portable, heated, semi-closed circle system anaesthetic machine. Induction time (time from injection of midazolam to detected maximal effect of midazolam) ranged from 12 min to 29 min. The maximal effect of midazolam was assessed as being either moderate sedation (n=9) or heavy sedation (n=2), and the maximal effect of inhaled isoflurane and oxygen was assessed as being light anaesthesia (n=11). The level of chemical restraint achieved using this combination allowed attachment of heart rate monitoring units and collection of biological samples. Recovery time ranged from 1 min to 11 min. The anaesthetic regime proved a practical, safe and reliable method for the immobilisation of lactating Weddell seals under conditions of low environmental temperature. © Springer-Verlag 2005.