Immobilization of Free-Ranging Steller Sea Lions (Eumetopias jubatus) with Butorphanol-Midazolam-Medetomidine.

The western population segment of the Steller sea lion (Eumetopias jubatus) has experienced significant population declines. The Alaska Department of Fish and Game is studying the ecology and health of the population. We describe the use of butorphanol-midazolam-medetomidine (BMM) in the capture of free-ranging Steller sea lions. This combination is advantageous as the animals retain their breathing reflex and float at the surface if entering water after darting, and it is fully reversible. Sea lions were darted when resting on haulouts. The majority (45/55) of the adult female sea lions received 75 mg butorphanol, 75 mg midazolam, and 20 mg medetomidine (n=44) or 18 mg medetomidine (n=1), whereas 10/55 were immobilized with lower doses: 30-62.5 mg butorphanol, 45-62.5 mg midazolam, and 9-18 mg medetomidine. Time from dart to approach was a mean of 19.7 min (range 9-45 min). The mean mass of the 29/55 sea lions where weights were obtained was 292.3 (range 205.5-380.5), and the mean drug dose administered in the dart to these was 0.23 mg/kg (range 0.13-0.36 mg/kg) butorphanol, 0.25 mg/kg (range 0.18-0.36 mg/kg) midazolam, and 0.07 mg/kg (range 0.04-0.10 mg/kg) medetomidine. No mortalities were noted. Twenty of the 55 sea lions were administered an additional 30-100 mg butorphanol, 37-75 mg midazolam, and 3-13 mg medetomidine after approach to achieve adequate sedation for handling. Forty-two of 55 sea lions were intubated and maintained on isoflurane and oxygen, whereas 13 were maintained on injected drugs alone. Of these 13 animals, five received supplementary oxygen. Early in the immobilization, heart rates, and blood oxygenation (SpO2) were significantly lower in the sea lions that received supplementary drugs (P<0.05), and sea lions not receiving supplementary oxygen were hypoxemic. The immobilization was reversed with atipamezole, naltrexone, and flumazenil intramuscularly. The mean time from reversal to ambulatory was 11 min (range 2-42 min). In conclusion, BMM was efficacious for immobilization of free ranging Steller sea lions.