Reversible immobilization of free-ranging adult male California sea lions (Zalophus californianus)

摘要

The study was conducted to test immobilizing agents using reversible anaesthetic protocols developed for California sea lions (Zalophus californianus) in captivity on free-ranging, healthy adult male California sea lions in a controlled field environment. The objective was to document the response time to immobilization and to different planes of anaesthesia of three different drug combinations in dosages that could be delivered remotely using a single dart. A total of six male adult California sea lion were captured on a haul-out trap in Astoria, Oregon, USA during September 2010. Each animal was weighed using a platform scale under the holding cage. Once weighed, the animal was moved into a squeeze cage, mechanically restrained using the squeeze bars, and given an injection of one of three drug combinations based on actual weight: 0.03 mg/kg medetomidine (40 mg/ml)+1.0 mg/kg of a 1:1 solution of zolazepam:tiletamine (100 mg/ml) (ME/T); reversal with 0.15 mg/kg atipamezole (5 mg/ml) (AT); 0.03 mg/kg medetomidine (40 mg/ml)+0.15 mg/kg midazolam (50 mg/ml) (ME/MI); reversal with 0.15 mg/kg atipamezole (5 mg/ml) (AT); or 0.03 mg/kg medetomidine (40 mg/ml)+0.15 mg/kg midazolam (50 mg/ml)+0.1 mg/kg butorphanol (50 mg/ml) (ME/MI/BU); reversal with 0.15 mg/kg atipamezole (5 mg/ml) and 0.1 mg/kg naltrexone (50 mg/ml) (AT/NA). The drugs were delivered intramuscularly (IM) over the pelvis, femur, tibia or in the shoulder of five animals using a hand syringe to ensure proper placement and to ensure that the entire drug dosage was administered. The last animal was darted in the right shoulder, while resting in the haul-out trap from a distance of 5 m using a Dan-Inject JM Special 16 dart rifle. The mean weight of the six males was 244.7 kg. The drug effect was defined as: light sedation (disoriented but alert); deep sedation (disoriented and lethargic, but still in control of head and neck); light anesthesia (no response to tactile stimuli, but slight response to intubation and sampling); and moderate anesthesia (immobilized, no response to stimuli or sampling). Respiratory and heart rates were monitored once the animal reached light sedation. Results revealed that the induction times varied based on the drug combinations. One animal given the ME/T combination was immobilized within 5 min, but died within 7 min of injection. One animal that received the ME/MI combination produced a steady progression from light sedation at 10 min to deep sedation and then to light anesthesia and finally immobilization at 20 min after injection. Reversal with AT was effective and the animal was released 12 min after receiving the reversal injection. Three animals that were given the ME/MI/BU combination showed that the time to induction average was 8.3 min and the average time to immobilization was 13.5 min . This combination also produced a steady progression from light sedation to immobilization. The reversal combination of AT/NA was given an average of 36 min after the initial injection of the anesthetic drugs and recovery time averaged 12.3 min. Time to full recovery and release was variable among the three animals, mostly due to variability in recovery time, with an average of 48 min but a range of 41-54 min. In this preliminary study of three reversible anesthetic drug combinations, ME/MI and ME/MI/BU was the most reliable and safe drugs for wild adult male California sea lions. The remote delivery of ME/MI/BU using the Dan-Inject darting system worked well in the controlled field situation with experienced darters and showed promise as a field technique.