The Art of Chemical Capture Advances in wildlife capture pharmacology By Michael D. Kock, William R. Lance, and David A. Jessup
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Credit: Satya Gautam Bhalla
Michael D. Kock (BVetMed, MRCVS, MPVM) is Senior Field Veterinarian for the Wildlife Conservation Society, based in the Western Cape, South Africa.
n the early 1960s, when Kariba Dam rose between Zambia and Zimbabwe backing up the Zambezi River to form Lake Kariba, thousands of wild animals—including antelope, black rhinoceros, carnivores, and reptiles—became stranded in a rapidly changing landscape. Conservationists soon began a wildlife salvage effort dubbed “Operation Noah,” which included some of the first efforts to chemically immobilize wildlife using dart guns. Those early efforts were well meaning, but many animals died, were injured, or just couldn’t be caught—a situation that was dangerous for both the wildlife and their would-be captors. Author A. E. Harthoon described the early days of chemical capture in his 1976 book Flying Syringe, in which he stated: “The successful handling of animals with drugs, capture in the wild, and restraint for various purposes can ultimately be performed successfully only by those who … put the animal first; by those who are guided by a code, as medical doctors and veterinarians are subjected to a code;
by those who have an awareness of the value of animal life; and by those who set their sights on the welfare of all animals with which they work ….” Those words still ring true today for wildlife professionals who practice “capture and immobilization,” which simply means rendering a wild animal unable to flee. This can be accomplished by physical methods (nets, traps, and ropes) or with chemicals—drugs that tranquilize, cause deep sedation, provide anesthesia, or yield a combination of the three (see chart on page 36). Practitioners of chemical immobilization often refer to it as “knock down,” and call the time from chemical darting to recumbancy “knock down time.” However, multiple variables affect the safety and effectiveness of the procedure, including drug type, dosage, dart weight and placement, length of time for the dose to take effect, length of time the animal is incapacitated, and ability to reverse the effects of the drug so the animal can recover safely. These variables must be carefully assessed or animals may suffer serious injury during capture such as “capture myopathy”—severe muscle damage and often death due to the combined effects of exertion, acidosis, hyperthermia, electrolyte imbalance, and fear during capture and handling. This and other problems came into play during “Operation Noah” at Lake Kariba, conducted at a time when the drugs used for chemical capture were very limited. Nicotine and succinylcholine, for example, were primitive and often highly toxic. Etorphine and acepromazine were better, but for some species and at some doses, injected animals would become excited and run to the point of exhaustion or death. Others suffered severe respiratory depression when the drugs’ effects peaked. In North America at that time, similar problems were occurring with deer, moose, bears, mountain lions, and other species.
Credit: Mark Gocke, Wyoming Game and Fish Department
Darted from a helicopter in Wyoming, this female moose has been anesthetized with a combination of thiafentanil, azaperone, and medetomidine (TAM) so she can be assessed and radio-collared. The anesthesia has left this animal sternally recumbent, semi-conscious (with eyes open but unfocused), breathing well, and calm enough to resist struggling— signs that TAM is well-suited for use in wildlife.
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The Wildlife Professional, Spring 2012
Today, half a century later, the drugs and delivery devices used for chemical immobilization have advanced tremendously. We have new pharmaceutical drugs, more-effective combinations, and © The Wildlife Society