Behavioral responses of New Zealand fur seals (Arctophoca australis forsteri) to darting and the effectiveness of midazolam and tiletamine-zolazepam for remote chemical immobilization

Abstract

We evaluated the behavioral response of 125 free-ranging New Zealand fur seals (75 females and 50 males) to darting and the effectiveness and safety of midazolam and tiletamine-zolazepam for remote chemical immobilization. Behavioral reactions to darting were minor and brief. Overall, severe reactions to darting such as long flight responses (7%) and escape to the sea (7%) were uncommon. Midazolam administered by dart failed to produce a satisfactory level of immobilization. Tiletamine-zolazepam was administered to 120 animals (35 females and 85 males), 104 of which were successfully immobilized and 16 escaped to the water following darting or attempted net capture. At least 10 of the 16 animals are known to have survived. Tiletamine-zolazepam caused moderate depression of swimming and diving behavior in the animals that escaped to the water. Data from dive loggers confirmed that seals that escaped remained near the sea surface for extended periods. Tiletamine-zolazepam administered by dart at a mean dosage of 1.87 ± 0.18 mg/kg for females and 1.49 ± 0.23 mg/kg for males provided effective and safe immobilization, reducing capture stress for both animals and personnel. Although there is still a risk of drugged animals escaping to the water and possibly drowning, this risk is much lower than previously reported for other pinnipeds.