Last updated February 15, 2018 at 11:03 am
New research – and new pictures – have highlighted the dramatic impact on polar bears that climate change is having in the Arctic.
Detailed monitoring of polar bears hunting for prey in the Beaufort Sea north of Canada and Alaska shows that many are unable to catch enough food to meet their energy needs.
The study, led by wildlife biologist Anthony Pagano, also revealed that polar bears in the wild have higher metabolic rates than previously thought.
As the Arctic warms and more sea ice melts, bears are having to move greater distances to hunt. This causes them to expend more energy during the summer, when they are fasting until the ice returns to the continental shelf in the autumn.
“We’ve been documenting declines in polar bear survival rates, body condition and population numbers over the past decade,” Pagano says. “This study identifies the mechanisms that are driving those declines by looking at the actual energy needs of polar bears and how often they’re able to catch seals.”
Pagano, who works with the US Geological Survey, carried out the work as part of his PhD research at UC Santa Cruz.
Burning more energy than polar bears can input
With colleagues, he monitored the behaviour and metabolic rates of adult female polar bears without cubs as they hunted on the sea ice in the spring. High-tech collars recorded video, locations and activity levels over a period of eight to 11 days, while metabolic tracers enabled the team to determine how much energy the bears were expending. The footage from the study revealed a rare insight into the life of polar bears.
The field metabolic rates they measured averaged more than 50% higher than previous studies had predicted. Five of the nine bears in the study lost body mass, meaning they weren’t catching enough fat-rich marine mammal prey to meet their energy demands.
“This was at the start of the period from April through July when polar bears catch most of their prey and put on most of the body fat they need to sustain them throughout the year,” Pagano says.
USGS researchers have been studying polar bears in the Beaufort Sea area since the 1980s. Their most recent population estimate indicates the population has declined by about 40% over the past decade.
The paper was published in Science.