Seth Stapleton tracks polar bears for a living, but these days he often does it from the safe distance of 380 miles out in space.

A wildlife biologist at the University of Minnesota, Stapleton and some friends hit upon the idea of tracking the huge white bears on the dark soil of a northern Canadian island via high-precision satellite photos rather than going there in person to count bears from a low-flying airplane.

The U’s research helps Canada manage its polar bear population, estimated at 10,000 to 15,000, which is a sizable share of the world population of 25,000. The idea is to determine how many bears there are and where they are spending their time.

The scientists discovered satellite bear tracking almost by accident.

“I talked to a few people and said in jest, ‘Wouldn’t it be funny if we could use Google Earth or other satellite imagery to do this work for us?’ ” Stapleton said. Funny or not, it turned out that it works.

Tracking the animals by satellite is possible because polar bears are big (adults are about 6 to 9 feet long and weigh 400 to 1,200 pounds) and satellites are precise enough to show anything that’s 20 inches across, Stapleton said. That means the polar bears show up as white dots against a dark landscape — but dots that move in photos taken over time.

Studying August and September satellite pictures of Rowley Island in Canada’s Foxe Basin, Stapleton found the bears were surprisingly easy to pick out.

“When the ice breaks up, the bears must move to land. On these small, flat islands there’s a high density of bears, 150 to 300, and the land is snow and ice free, so there’s no confusing other things with a bear,” he said. “We can even measure the dots in the photo to a certain extent. A polar bear is four to eight pixels wide, depending on whether it is standing, sitting or stretched out.”

Stapleton is clearly a man fascinated by polar bears.

“They’re at the top of the food chain, and that makes them very interesting,” Stapleton said. “And they’re closely linked to sea ice, which, with the warming environment, makes them an interesting case study. What will happen to them as the ice changes?”

There’s no easy answer to that, he said.

“It’s not as simple as saying that less sea ice means fewer bears,” Stapleton said. “It depends on the location and the types of ice available — some types of ice are better for the seals that the bears eat. But in some areas the warming temperature is predicted to have negative effects. If there’s not enough ice for the bears to hunt on, they spend more time on land, and that’s physically stressful for them.”

The U scientists still make trips to polar bear country, but, as a result of the satellite photos, not as many as they did before.

“It’s very expensive to conduct research in the Arctic, hundreds of thousands of dollars, depending on the project,” Stapleton said. “And flying aircraft in the Arctic is not the safest endeavor. The weather can turn south in a hurry and make it difficult to return to camp.”

Satellites also can access places that can’t be reached by a plane or helicopter. “The trade-off is that you don’t get nearly the same detailed information,” Stapleton said. “If you capture a bear and get samples, you can determine its health, body condition, age and reproduction capability. Satellite imagery doesn’t give you that level of information, but you do find out where bears are distributed and how many are in a given area.”

Many of the digital photos Stapleton uses come from DigitalGlobe Inc., a commercial satellite company in Longmont, Colo., whose photos typically cost several hundred dollars each and were recently used in the search for the missing Malaysian airliner.

Those satellite photos will become even more detailed after DigitalGlobe launches its new WorldView-3 satellite in August, said Kumar Navulur, the firm’s director of next-generation products. While existing satellites can distinguish objects as small as about 1 ½ feet wide, the new satellite will be able to see objects only a foot wide, which is precise enough to identify individual manhole covers in a street, he said. In addition, the new satellite will produce more consistent images by using a sensor to correct photos for the amount of moisture or dirt particles in the atmosphere.

“The atmosphere is always changing, and this sensor will even help in the search for polar bears,” Navulur said.

But using satellites to track polar bears is still in its testing phase. Its usefulness will be determined partly by how far the orbiting camera technology can be pushed. For example, if Stapleton and others can figure out how to use satellite photos to detect white polar bears on ice, it will allow them to track the bears in more seasons of the year. The costs of satellite tracking are also up in the air because the satellite photos can cost different amounts depending on whether the U gets photos from commercial firms such as DigitalGlobe, or from government agencies that already have purchased the pictures, Stapleton said.

“There hasn’t been enough work done yet to guess at the total cost of satellite images,” Stapleton said. “But I expect satellite imagery to get cheaper, and field work to remain costly.”