Use of midazolam/pethidine and tiletamine/zolazepam combinations for the chemical restraint of leopard seals (Hydrurga leptonyx)

We immobilized 200-550-kg leopard seals (Hydrurga leptonyx) on sea ice in Prydz Bay, Antarctica (68degrees25'S, 77degrees10'E) between November 1997 and February 2000. Midazolam (0.18-0.2- mg/kg)/ pethidine (1.0-1.5 mg/kg) was administered by dart to 16 leopard seals. Unpredictable immobilization, poor air-way maintenance, and our inability to fully assess the suitability of flumazenil (0.003-0.01 mg/kg), naloxone (0.01-0-013 mg/kg), and naltrexone (0.05-0.12 mg/kg) as reversal agents limited suitability of midazolam/ pethidine. Tiletamine/zolazepam 1:1 (0.5-1.5 mg/kg) was, therefore, administered to 19 leopard seals. It produced faster induction (19 +/- 3 min), more effective and reliable response to dose (rank correlation: r, = 0.88, n = 18), and better pulmonary ventilation and faster return of cognitive function upon recovery, in comparison to midazolam/pethidine, Best results were achieved with tiletamine/zolazepam (1.2-1.4 mg/kg) which safely immobilized seven of nine seals for 20-30 min. Entry to the water upon darting was minimized, but not eliminated, by the use of lightweight air-pressurized darts and a thorough knowledge of leopard seal behavior.