Chemical Restraint of the Fisher

As fisher (Martes pennanti) populations recover throughout portions of their historic distribution in the southeastern United States, responsibilities and opportunities in their conservation research likely will become more prevalent. Chemical restraint often is a valuable tool in studying wildlife populations. We reviewed previous research on chemical restraint of fishers with the objective of providing a comparative assessment of field and clinical applications of specific chemical restraints or chemical restraint combinations. Chemical restraints that have been studied in fishers include ketamine, Telazol, and combinations of ketamine-xylazine, ketamine-medetomidine, and ketamine-acepromazine. Ketamine was safe and effective, but when used alone, its applications were limited to brief, non-invasive procedures because it generally provided shallow immobilization and rapid recovery. Telazol was more versatile than ketamine because it provided better myorelaxation, more efficient ventilation, and dose-dependent duration of anesthesia. Telazol would enable brief or prolonged procedures at doses of 5.0-11.0 mg/kg. We considered medetomidine-ketamine combinations and atipamezole to be a preferred alternative to other chemical restraints because these drugs combined broad clinical and field utility with reversibility. Medetomidine-ketamine at 0.07-0.08 mg/kg medetomidine combined with a 3.5-4.0 mg/kg ketamine, and atipamezole at approximately 0.35-0.40 mg/kg (administered upon completion of procedures) would be appropriate for most management and research objectives. Ketamine-xylazine, although generally effective, was the only drug or drug combination associated with clinical concerns (respiratory complication). Generally, physiologic responses of fishers were consistent with known drug pharmacologies. Fishers may be prone to hyperthermia and mild hyperventilation during immobilization with ketamine or ketamine-?2-agonist combinations, respectively. Our recommendations and precautions can be a useful guide for restraining fishers. However, no chemical restraint or dose regimen should be perceived as a panacea, so managers and biologists must base selection of a chemical restraint and determination of an appropriate dose on specific objectives and attributes (e.g., physical condition of the fisher) of the restraint event. Further research on chemical restraint of fishers should focus on refining field immobilization protocols, clinical evaluation of cardiopulmonary regulatory mechanisms mediated by ?2 receptors, conditions associated with thermoregulatory disruption, and new chemical restraints (particularly ketamine-?2-agonist combinations).

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