Chemical immobilization of Weddell seals (Leptonychotes weddellii) by ketamine/midazolam combination.

Objective: To provide reliable, effective immobilization for Weddell seals under extreme field conditions using an injectable ketamine/midazolam combination.

Study Design: Observational study.

Animals: Thirty adult Weddell seals (12 male, 18 female) in Erebus Bay, Antarctica, body mass (mean +/- SD) 412 +/- 47 kg, aged 9-27 years.

Methods: Seals were immobilized with a target dose of 2 mg kg(-1) ketamine hydrochloride and 0.1 mg kg(-1) midazolam hydrochloride (IM), based on visually estimated body mass. When required, maintenance doses were administered at a target of 0.5 mg kg(-1) ketamine hydrochloride and 0.025 mg kg(-1) midazolam hydrochloride (IV).

Results: Complete immobilization was achieved in 33 of 40 injections (14 of which were repeat events on the same individual). Time to immobilization averaged 12 +/- 4 minutes, with a duration of initial immobility of 38 +/- 19 minutes. Total immobilization time varied by handling protocol, including condition assessment and muscle biopsy (Protocol 1, 60 +/- 13 minutes), condition assessment and instrument attachment (Protocol 2, 154 +/- 13 minutes), and condition assessment, muscle biopsy and instrument retrieval (Protocol 3, 48 +/- 8 minutes). Overall, a total immobilization time of 114 +/- 60 minutes was accomplished with 4 +/- 4 maintenance doses, and an average recovery time of 36 +/- 17 minutes. Most effects of the anesthetic combination were unrelated to mass, age, sex or total body fat. However, leaner seals had longer duration of initial immobility (% and kg total body fat) and recovery times (kg fat). Apnea events were uncommon and treated effectively with doxapram. No animals died.

Conclusions And Clinical Relevance: Reliable and effective field immobilization of Weddell seals was accomplished with a low dose of ketamine hydrochloride and midazolam hydrochloride, utilizing IM injection initially and IV maintenance methods.