What to do after catching a polar bear?

Written by Su Chengyu

Jon Aars is a biologist specialising in polar bears at the Norwegian Polar Institute (NPI).

Since 1987, scientists from the institute have conducted field trips to Svalbard every year, searching for polar bears in the ice-covered wilderness, trying to catch them, and then studying them.

The Norwegian Polar Institute was established in Svalbard, Norway in 1968. Photo taken in 1999. Source: npolar.no

Aars is making his annual research trip this year, too. The trip is timed in early spring, when mother polar bears and their cubs are out looking for food and the sea ice is thick enough to be safe to walk on. Most importantly, it is safe for helicopters to land on the sea ice.

In addition to the pilot and the aviator, the helicopter will also carry a biologist, a veterinarian, and himself.

Finding a polar bear is not an easy task. The white coat of a polar bear can conceal it and make it blend into the white ice field. Aars could only look for polar bear footprints from the sky and then follow the footprints to the end. Finally, he found a little bit of light yellow in the white world. That was a polar bear, but not just one, but three: a mother bear with two cubs.

Image credit: Jon Aars

After locking the target, Aars sniped it with a tranquilizer gun with a sight. After all, he was not a novice, and he hit it successfully. The polar bear fell down within a few minutes.

Image credit: Jon Aars

Image credit: Jon Aars

The sedative has a time limit, so the helicopter must land on the nearby ice as soon as possible. The researchers rushed to the polar bear and covered its eyes with a blue scarf to prevent it from being blinded by the sun when it wakes up. At the same time, Aars will place various instruments around the bear to detect the polar bear's heart rate, blood oxygen content and body temperature.

Image credit: Jon Aars

The items measured every year are the same, such as the polar bear's length, chest circumference, and skull size, which are basic data. To know the age of a captured polar bear, scientists will check its teeth. Generally speaking, no matter what kind of bear it is, their tooth shape will change as they age.

If a bear is older and uses its teeth longer, the teeth will be more worn, the color will become darker, and the spots on the enamel will become larger. According to the different degrees of wear, the researchers will divide the bears into 6 age groups, young bears (

The above data on polar bears are relatively easy to obtain because they are easy to operate. The trouble lies in weighing. An adult female polar bear weighs about 150-300kg. It takes at least two researchers to get it on the scale, and then one person lifts it. This is under the condition of being skilled. Forget about male bears. They weigh more than twice as much as female bears, about 350-700kg. No matter how skilled you are, you can't move them.

Weighing process Source: Jon Aars

After measuring the weight, the next step is to collect samples. There are not many samples to be collected, just a little blood, fur and fat. In order to prevent the blood sample from freezing, Aars will put the collection tube containing the blood sample into the lining of his clothes, close to his chest, and use his body temperature to keep the blood sample warm.

Blood sample testing is the main method to understand the basic physiological data of an animal. In addition to routine blood tests, parasite blood tests can also be used to understand whether polar bears are infected with parasites; if pollutants are detected in the blood sample, it means that there is a problem with the polar bear's living environment (in 2018, scientists found hundreds of toxic chemicals in polar bear serum).

Image credit: Jon Aars

Fat samples can provide insights into the polar bears’ diets: Quantitative fatty acid analysis can reveal what kind of meat the bears ate, such as ringed seals or Atlantic walruses, or the carcasses of stranded bowhead whales.

Collecting hair can obtain its DNA, understand the genetic information of the local polar bear population, and outline the family tree of the bear family.

After the samples are collected from the mother bear, a collar is also put on the mother bear, which is equipped with a GPS system to track its location and roughly understand its activities. The collar also has a monitor to monitor salt changes, and researchers can calculate the time the polar bear has been swimming in the water based on these values.

Finally, the researchers will put several marks on these bears. An ear tag with a chip on it; a number will be tattooed on the lip; and of course a number will be written on the back, but this is short-term, because the mark on the back will disappear after the polar bear molts next time. When researchers see a polar bear with a mark on its back, they will not catch it. If the same bear is caught in the same season, the collected samples are equivalent to duplication, which is time-consuming and laborious. Of course, there are also benefits for the bears. Who would want to be the unlucky one to be caught by scientists twice in a row?

The whole process of capturing, sampling and marking takes about an hour, but this time Aars encountered a mother bear with two cubs, which took a little longer than usual. The two cubs were not sampled or marked because only the adults were studied.

After Aars took off the scarf covering the polar bears' eyes, he did not leave immediately, but waited for the three bears to wake up and made sure they were all fine before leaving. Aars was not afraid that the three bears would pounce on him and eat him after waking up, because he knew that the polar bears would not understand what was going on because their brains were still buzzing after waking up.

It seemed that nothing was wrong, so Aars and his colleagues got on a helicopter to look for the next bear.

References

[1] https://www.cnn.com/2020/09/30/world/puffins-maine-kress-c2e-scn-spc-intl/index.html

[2] https://phys.org/news/2018-12-hundreds-unrecognized-halogenated-contaminants-polar.html

[3] https://www.sciencedirect.com/science/article/abs/pii/0091305790903115

[4] https://www.sciencedirect.com/science/article/pii/S1470160X21009109