“Here you are flying at about 20 knots or so; you are chasing a bear so you can get close enough to dart it. The wind is rushing in your face, and it’s 10 below zero or more.” George Durner, research zoologist with the United States Geological Survey, Alaska Science Center, told Frontier Scientists that he feels neither cold nor frightened while doing bear capture work. “Never once have I leaned out of the helicopter window to dart a polar bear and noticed the temperature. Your adrenaline is going so much.”
It’s not easy work. It’s normal for spring temperatures over Arctic sea ice to measure -30 degrees Fahrenheit. Maybe colder. Maybe mix in strong winds and obscuring snow. Durner’s mind isn’t on the cold because he’s concentrating on the job. “There’s just too much going on that you have to focus on: basically getting an effective hit with the dart and making certain it’s done safely for both the people on the helicopter as well as for the bear.”
“The immobilizing drug we use is a safe drug for bears and for humans. It’s quite effective– induction usually occurs within 4 minutes after injection.” Durner said “When induction occurs they begin to stumble a lot and they fall over, you can be fairly confident that the drug has taken effect and they are safe to approach.” Once a bear is immobilized the scientists take a series of measurements and samples: size and weight, age and gender information, small samples of blood and fat tissue. They also apply tracking devices in the form of collars or tags glued to fur. “We’ve been able to amass hundreds of thousands of locations since 1985 on the movements of polar bears in the Beaufort Sea and the Chukchi Sea.”
Todd Atwood leads the polar bear research program at the USGS Alaska Science Center. Atwood, a biologist, explained physical capture is only one means by which polar bear samples are taken. Other techniques, like hair-snags that pull free a few hairs from passing polar bears, are also used and the scientists continue to explore other methods. Atwood said that captures are still necessary because “We do get a lot of very valuable information from having the bears in front of us and being able to collect samples from them. But over the last three years we’ve reduced the number of bears we capture by about 30%,” accomplished by adding different sampling techniques.
The data from polar bear captures allows scientists to assess the health of individual bears, estimate the size and trend of the population, identify the habitats preferred by polar bears and get a grasp on how polar bear movement and distribution have changed in response to changing habitats. Atwood explained “We are interested in how changes in the physical environment, mainly the deterioration of the sea ice ecosystem, is causing changes in individual health and population changes– how that’s affecting reproduction and survival.”
Capture and collar technology
Technological advances keep upping the game on polar bear tracking. Durner described: before 1985 the tracking collars emitted very high frequency (VHF) radio waves and could only be located by flying aircraft equipped with radio antenna long distances across the Arctic pack ice. Aircraft would have to approach within 10-20 miles of the bear to receive the VHF signal. Once the signal was received, telemetry was used to narrow down where the collar’s bleep originated from and to home-in on the bear. Beginning in 1985 collars with ultra high frequency (UHF) radio waves were deployed. Those transmitted data to satellites which in turn transmitted the data to a ground receiving station, which processed the data and estimated locations of collared bears. In 2004 collars were upgraded with GPS receivers– the data from which was also sent through the UHF signal. The location data from UHF transmitters, sent along to scientists’ computers, provided data that has allowed USGS to show how polar bears interact with their sea ice habitat. Durner said over the years technology improvements have “Provided us a much finer look at their movements and distribution.”
During polar bear capture work collars are fitted onto female polar bears. Atwood explained “The females have these nice prominences running along this part of their skull that allows them to retain a collar.” In contrast males’ more heavily muscled and fat-bearing necks make their head and neck together almost triangular; it’s so easy for collars fitted to males to come off that it’s not really worth it. To track male polar bears the scientists are exploring other methods, like gluing a tracking tag on the bears. Atwood said “They retain them for about 60 days. The limiting factor is that once they molt their coat that tag falls off with the hair because we epoxy it onto the hair.”
Collars give more data than tags and are big enough to carry more specialized equipment. The research team keeps collars on females for 12 months, then a mechanism on the collar is programmed to make the collar fall off. The collars don’t need to be retrieved because they send data to satellites. Processing units on the collars can be programmed to broadcast location data in increments from once every 15 minutes to once every several hours.
Extreme Arctic cold is tough on batteries, which means the scientists have to be careful about how they program the collars. Atwood said “In reality these batteries will probably go for two years. But we only like to deploy the collars for one year because we’ve found this release mechanism works flawlessly when you program it to drop off in a year. It begins to decline in efficacy if it goes much longer than a year. So we are conservative with that. The last thing we want to do is to not have these collars coming off of bears and so we’ve taken some great pains, and we’ve sacrificed data, to make sure that they come off.”
Mapping a line on sea ice
It’s “Very important to understand how individuals behave or move about during the course of a 12 month period,” Durner said. “The focus of my work is to find out to see if we can discern what sea ice characteristics are important for polar bears.” Comparing where polar bears travel to satellite-imaged sea ice history lets the scientists establish what preferred polar bear habitat looks like. That’s relevant right now because hunting seals, polar bears’ most vital prey, means using the sea ice platform. Atwood explained in our changing climate “The sea ice platform that the polar bear uses to hunt ringed and bearded seals is available for a decreasing amount of time each year. When that platform melts away, polar bears can’t access prey.”
Durner: “We’ve been able to analyze polar bear location data, relative to the sea ice data, to develop models that describe the habitat that’s most preferred by polar bears and that has allowed us to map where these habitats are, how they change by seasons and how those habitats have changed during the observational period.” Their findings underline how “Distribution of sea ice is extremely important for polar bears.”
Atwood: “The reason why polar bears are important beyond their intrinsic value is they are a sentinel to change in a sentinel system. They are the apex predator, they provide really interesting insights about the food web, and so we can detect changes in the food web through polar bear condition indices. And everything in the research community indicates we are on a path to lose a large percentage of the circumpolar polar bear population.”
Laura Nielsen 2015
Frontier Scientists: presenting scientific discovery in the Arctic and beyond