7/4/2014 4:39:51 PM
Studying Polar Bears In Svalbard, the Norwegian Arctic
Editor's note: The Norwegian Polar Institute has been conducting a long-term annual monitoring study of polar bears in Svalbard since 1992. A key focus of the research includes understanding how habitat use and individual survival and reproductive rates may be influenced by environmental changes such as sea ice losses from climate change. As part of the study, scientists sedate a sampling of polar bears by remote darting from a helicopter every spring. Sightings from people visiting or living in the area also add to their understanding.
Our fieldwork takes place in April. This is the period when female bears in the area have left their maternity dens, making it possible for us to get good data on their reproduction. Furthermore, in most years the sea ice is solid at that time, which allows us to sedate the bears and land our helicopter without risk to bears or humans.
After we dart a bear, it usually takes only a few minutes before it is immobilized and can be approached safely. The first time an individual bear is captured, we mark it with ear tags and tattoos. Thus, if the same bear is recaptured in later years, we can use the individual capture histories to estimate polar bear survival rates. In many cases, we can also determine whether or not cubs have survived. Polar bear cubs stay with the mother for more than two years. Thus, if adult females reproduce more frequently, or if they are alone the year after being caught with young of the year, we can assume that the cubs died.
Every year we equip about 10 to 20 adult females with satellite radio collars. This allows us to follow their movements and to see how they use the sea ice or land through the year. Furthermore, data from the collars reveal if females go into maternity dens in winter to give birth. (Polar bears, unlike brown bears, only den for prolonged periods in winter when they are pregnant; in other years, they continue to hunt through the cold and dark winter.)
The data we obtain during the annual spring capture program is thus limited to what we sample and record on the day we handle an animal, plus the movement and behavior data that we receive from collared female bears. However, another source of important data comes from people who observe polar bears in the wild and report their sightings to us. In many cases, such observations are of polar bears with known identities.
Insights from Tourists
When we handle a bear in spring, we paint a number on its rump. This makes it possible for researchers to avoid handling the same bear more than once each spring, and provides us with some extra data on the movement of that bear if encountered again. Because the number remains on the bear until the hairs are shed in late summer, observers are able to report which individuals they've seen.
Such reports are often very valuable. For example, cub survival rates during the first year of life are very low in Svalbard. Only about one in three cubs survive from the time they leave the den in March or April until the next April. But we know little about when the cubs die. Thus, we welcome reports from people who sight mother bears with or without their cubs at different times in the summer. Furthermore, photos of the bears make it possible for us to see the condition of the bears, which is important for understanding how they are doing.
Reports This Year
This year, we've received reports of several bears with painted numbers, mainly from tourist ships sailing around the islands. Two of these observations were of females that had cubs with them in the spring. One mother (N23881) was captured with one cub in northern Spitsbergen, the largest island in the Svalbard archipelago, in late April. This female's range is very local: both the capture (see map above) and tracking data from this year (see map below) show that she spends much of her time in Raudfjorden, a small fjord facing north. The mother is 11 years old. Two reported sights of this bear from tourists this year confirm that the cub has survived so far (see photos below by Stephanie Kiel).
Another female was captured with two cubs in Van Keulen, west of Spitsbergen, in early April. A report from a local trapper confirmed tracks of the mother and two cubs in late May. Later, a bird biologist reported the mother and the cubs ate eggs from nests in his study colonies. The family, tracked by the collar, then moved north and crossed Isfjorden, the fjord leading to Longyearbyen, the main settlement in Svalbard. Two different reports lately confirmed the mother still had two cubs after this 14-hour-long swim across the fjord. Among the people that have reported about the bears this year are the well known polar bear biologists Ian Stirling and Nikita Ovsyanikov, both operating as expert guides on tourist ships sailing around the islands.