Chemical Immobilization for Polar Bears

The polar bear (Ursus maritimus) is found throughout the Arctic region. These animals travel long distances over vast expanses, often on drifting oceanic ice floes, searching for seals, their primary prey. Polar bears are stocky in build, with a long neck, relatively small head, short, rounded ears, and a short tail. Males, which are much larger than females, weigh in at 410 to 720 kg (900 to 1,600 pounds), and are around 1.6 meters (5.3 feet) tall at the shoulder and 2.2–2.5 meters in length. With the exception of one subspecies of grizzly bear, the polar bear is the largest and most powerful land carnivore.¹ The polar bear has no natural predators and knows no fear of humans.

Polar bear mating occurs in Spring, and implantation of the fertilized ovum is delayed. Including the delay, gestation may last 195–265 days, and one to four cubs are born during the winter in a den of ice or snow. Cubs weigh less than 1 kg at birth and are not weaned until after they are two years old.² Young polar bears are routinely killed by unrelated adult males; for this reason, female polar bears are extremely defensive of their cubs when adult males are present. The young usually remain with their mothers until they reach sexual maturity, with females first reproducing at four to eight years of age. The males mature at about the same age as females but do not breed until a few years later. Longevity in the wild is approximately 25 to 30 years, but polar bears in captivity have lived to more than 35 years old.¹

Polar Bears: Populations and Predation

Through the 1950s and 1960s, there was a marked increase in recorded numbers of polar bears being killed for their hides, giving rise to world-wide concern that the species might be endangered. At a meeting in Fairbanks, Alaska 1965, representatives of circumpolar arctic nations discussed conservation of polar bears and concluded that international coordination of research and management efforts was essential.³ By 2020, an estimated 22,000 to 31,000 polar bears were living in the wild.

Polar bears are an ice-dependent species that rely on sea ice as a platform to hunt ice seals and to raise their young. They are generally solitary and completely carnivorous, feeding mostly on ringed seals, but also on bearded seals and other pinnipeds. The bear stalks seals resting on the ice, ambushes them near breathing holes, and digs young seals from snow shelters where they are born.³ Polar bears prefer ice that is subject to periodic fracturing by wind and sea currents, because these fractures offer seals access to both air and water. As their prey is aquatic, polar bears are excellent swimmers, and they are even known to kill beluga whales.² Polar bears are opportunistic as well as predatory: They will consume dead fish and carcasses of stranded whales and eat garbage near human settlements. The latter often puts them at odds with human populations, occasionally requiring the intervention of wildlife managers.

Chemical Immobilization and Formulations

The capture and handling of free-ranging polar bears is an important tool for wildlife research, conservation, and management. However, live capture can expose individual animals to risk of injury or mortality. The polar bear is a species that has generated an abundance of concern amongst conservationists throughout its range due to climate change and shrinking habitats. While field studies using less-invasive methods such as aerial surveys can provide insights into polar bear populations, the physical capture, marking, and recapture of individual animals remains an important approach for population assessment. Additionally, live capture is sometimes the only means of collecting certain types of biological samples, measurements, and information on reproduction, age structure, and survival rates.² Regardless of the reasons for live capture, the immobilization and restraint of individual bears entails some risk.

In the mid-1980s, a mixture of the dissociative anesthetic tiletamine hydrochloride and the tranquilizer zolazepam hydrochloride (ZT) emerged as the preferred drug for immobilizing free-ranging polar bears.⁴ Available under the trade names Telazol and Zoletil, this formulation has several advantages, including full immobilization with a single injection (dart), a wide tolerance to overdosing, effective partial immobilization upon underdosing, maintenance of high respiratory rates that allow bears to thermoregulate while immobilized and a mortality rate of less than 1 in 1,000 captures.^4,5

In 1981, Lee et. al. reported using a concentrated solution of 200 mg Ketamine HCl and 200 mg xylazine HCl/ml for the immobilization of free-ranging polar bears. “A mean dosage of 6.8 mg of each drug/kg body weight was successful in immobilizing polar bears older than one year and 2.8 mg of each drug/kg body weight was effective for cubs. Male and female polar bears responded similarly to the drugs. Immobilization was characterized by slow, deep breathing, relaxed muscles, no excess salivation and no convulsions. The combination of ketamine and xylazine appears to be a useful alternative to drugs previously used for immobilizing polar bears.”⁵

As above, the Handbook of Wildlife Chemical Immobilization (Arnemo & Kreeger, 2018) recommends tiletamine hydrochloride and zolazepam hydrochloride at a dosage of 8 mg/kg for polar bears. This may be supplemented with ketamine at 2 mg/kg.⁶ Chemical Immobilization of Wild and Exotic Animals. (Nielsen, 1999) recommends both the ketamine-xylazine and tiletamine-zolazepam combinations, as well as an option of medetomidine in dosages of 0.04—0.06 mg/kg combined with 2.5—4 mg/kg of xylazine.⁷