How big are these big bears?

Brown bears fatten up for winter hibernation in Katmai National Park and Preserve in Alaska. And, since Wednesday, thousands of viewers around the world have tapped into Fat Bear Week to watch the bears gobble up Brooks River fish, estimate how well they pack, then vote for the biggest of a single elimination tranche.

But how big are these big bears? A winner will be crowned on October 5, but webcam viewers – nearly 650,000 votes cast last year – and actual visitors – 15,000 came to Brooks Falls to see the bears in 2019 – are just guessing. But there is hope for greater accuracy: Geographic information systems specialist Joel Cusick is pioneering a new technique for calculating bear weights that has broader implications for the bear weight. non-invasive wildlife research.

The idea came to Cusick, who works for the National Park Service in Alaska, in 2018, while he was working on mapping and surveying in Katmai. A terrestrial lidar scanner, which uses lasers to determine distance and other measurements, was available to measure buildings. It’s the device traditional civil engineers use, but when Cusick traveled to Brooks Falls and stood on a viewing platform 300 feet from the bears, inspiration struck. He thought: Why not use the scanner to measure the volume of a bear’s surface instead?

“I had laser feedback from the butt of Otis, one of the most famous brown bears out there,” Cusick said. “I was like, ‘Wow, this might work out. “”

Lidar, which stands for “light sensing and ranging,” emits beams of light to measure three-dimensional objects or areas. When light waves hit an object, they bounce back and return to the sensor. Computers then use the speed of light to calculate the distance between the sensor and all the points. This figure is then processed using software capable of modeling an object in three dimensions. Scanners have become standard technology that is deployed from the ground, the sky and satellites to measure vegetation growth. Now they are used to measure the length, height and girth of bears.

And bears like Otis, a legendary former Fat Bear Week champion, are actually quite suitable for lidar scanning. Katmai bears are usually weighed in the spring, when they are lighter, using a pulley system. But the process is resource intensive; it usually involves a helicopter and requires the bear to be tranquilized. The 4.1 million acre park in southwest Alaska (home to more than 2,000 bears) is already isolated and mostly accessible only by air. “In the fall, the weight of these bears has always been a big mystery because they just can’t weigh them,” Cusick said.

The devices only need 3 to 11 seconds to pass over the animal; since the bears are currently preoccupied – fishing for salmon swimming upstream to return to the spawning grounds – they stay relatively still while they wait.

“I didn’t expect them to be as still as they are,” said Cusick, who described them as “standing like statues”.

Initially, it seemed that their thick fur could prevent the laser from penetrating enough to be precise, but the damp environment and haze cover it enough to get a good reading. If they are partially submerged, however, this becomes a challenge; the laser cannot sweep in the water. Also, Cusick needs to get a good record of the bears’ bellies, which are full of fish, berries, and other foods.

“If we can get their belly to swing right above the water, that’s the biggest percentage of their volume and that’s what we’re hoping for,” he said. “It’s a lot of patience, standing like a photographer, waiting for a perfect shot. We do the same with lasers.

Inspired by his success, Cusick returned in 2019 and 2020 with a more accurate and faster scanner. His work confirmed that people voted for the biggest bear last year: Bear 747. (Bears are numbered by the park for research purposes.) The winner’s volume was 22, 6 cubic feet or 1,416 pounds, compared to the finalists, which followed the aptly named 747 at 1,250 pounds – Bear 32, or “Chunk” – and 1212 pounds Bear 151, or “Walker.” The internet sensation began humbly in 2015 as part of a National Park Service effort to educate the public about bears, which can gain up to four pounds a day by preparing for winter, and their ecosystem. surrounding.

There is still work to be done regarding the precise conversion of volume to mass. “The trick to getting the mass of the bear is knowing the density in pounds per square inch,” Cusick said. “This is the part of the equation that is still not determined.” He used a rough estimate to calculate the weight, estimating that bears are 60% water and 40% fat.

Big bears are not being scanned this year due to COVID-19 and personnel constraints; Cusick is always accompanied by a “bear instructor” who knows bears. (The voting process remains the same this year.) But other researchers are eager to continue work in their own areas of expertise. “I’m trying to get all of the ‘logues’ I work with to enter the 3D world that is possible with this type of terrestrial laser scanning on the ground,” Cusick said. “It’s a fast growing technology.

And “logues,” as he calls them – mostly bear biologists, so far – are interested. “I’m really excited about his work,” said Lindsey Mangipane, polar bear biologist with the US Fish and Wildlife Service. “It shows a lot of promise.”

A recent study shows that the mass of polar bears is an accurate measure to assess the links between what bears eat and how the population is doing. As the pack ice melts, bears spend more time on land, where they do not have access to their traditional prey, such as ringed and bearded seals.

Mangipane and others are working on a study using captive polar bears in zoos, which are trained to ride on scales and already have a known weight, to assess the accuracy of the scanning method. Analysis would be performed throughout the year to ensure that the shape of the bears – how fat or skinny they are – does not skew the results. The tests could start in the year.

If the lidar scan proves accurate for polar bears in captivity, scientists hope to use it as a non-invasive tool in the wild. Less reliable sea ice means the work of biologists has become more dangerous than before.

“We used to go and catch polar bears on the ice,” Mangipane said. “In the last few years the ice was not good enough for us to go out. It is important in the future that we have new ways of getting the data we need to make more informed management decisions.

Kylie Mohr is a writing intern for High Country News, Montana. This story originally appeared in HCN on September 29, 2021. Find it at www.hcn.org/articles/north-bears-just-how-fat-are-the-fat-bears.