IMMOBILIZATION OF FREE-RANGING MALE PACIFIC WALRUSES (ODOBENUS ROSMARUS DIVERGENS) WITH CARFENTANIL CITRATE AND NALTREXONE HYDROCHLORIDE

The major challenges in immobilization of free-ranging walruses (Odobenus rosmarus divergens) are to produce a deep level of anesthesia very quickly (to avoid darted animals from entering the water and drowning), and to find a drug or drug combination that requires only a small volume to be delivered by dart, is safe, reversible, and that provides an adequate period of immobilization to permit attachment of instruments, phlebotomy, and measuring. Tiletamine-zolazepam is recommended for immobilization of pinnipeds, with inhalant anesthesia recommended for more extensive procedures requiring better analgesia. Drugs that have been used on free-ranging walruses include ketamine, phencyclidine combined with acepromazine, etorphine, tiletamine-zolazepam, medetomidine and ketamine, and carfentanil. Carfentanil but not etorphine is presently licensed and available in the United States. Carfentanil at a dose of 2.7-3.0 mg was effective at rapidly immobilizing adult male walruses on a land haul-out. Carfentanil immobilization of Pacific walruses resulted in muscle spasms, which have been noted in six Atlantic walrus (Odobenus rosmarus rosmarus) immobilized with carfentanil. This reaction made manipulation of the animals more difficult and prevented placing of an endotracheal tube, which would have allowed assisted respiration. All walruses were apneic for an extended period after being darted with carfentanil. Carfentanil anesthesia was reversed with naltrexone hydrochloride (Wildlife Pharmaceuticals, Fort Collins, CO 80524) administered with an 18-gauge, 10-cm needle or with a 14-gauge over-the-needle catheter into either the epidural venous sinus or the caudal gluteal vein. After experiencing some deaths, we adopted a protocol wherein at 11 min postdarting with carfentanil (or as soon thereafter that we could approach the animal), we gave 150 mg of naltrexone hydrochloride IM and a second dose of 150 mg naltrexone IM or IV was given at 13 min postdarting.