At this rate, polar bears could go extinct much faster than we thought.This is the conclusion of a study published in the journalScienceshowing that polar bears have higher metabolic rates than previously thought, and as climate change alters their environment,increasing numbers of bears cannot hunt enough prey to meet their energy needs, which will inevitably lead to their demise.
The study revealsthe physiological mechanisms behind the observed declines in polar bear populations: “We have been documenting declines in polar bear survival rates, body condition, and population numbers over the past decade. This study identifies the mechanisms that are driving those declines by looking at the actual energy needs of polar bears and the how often they can catch seals, “explains Anthony Pagano, leader of the work.
The researchers monitored the behavior, hunting success and metabolic rates of adult female polar bears without cubs as they hunted for prey on the sea ice of the Beaufort Sea during the spring. Thehigh-tech necklaces affixed to bearsrecorded videos, locations and activity levels over a period of 8 to 11 days, while metabolic tracers allowed the team to determine how much energy the bears consumed.
Field metabolic rates averaged more than 50% of what 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 beginning of the period from April to July, when polar bears catch most of their prey and get most of the body fat they need to sustain themselves throughout the year,” Pagano said.
The devastating effects of climate change
Climate change is having dramatic effects on Arctic sea ice , forcing polar bears to travel greater distances and making it difficult to catch their prey. As the Arctic warms and more sea ice melts, bears have to travel much greater distances than before. This causes them to expend more energy during the summer, when they are fasting until the ice returns to the continental shelf in the fall.
“We found that polar bears actually have much higher energy demands than had been predicted. They must catch a large number of seals, ” says Pagano.
In spring, polar bears mainly feed on recently weaned ringed seals, which are easier to catch than adult seals. By fall, the young seals are older and wiser, and polar bears cannot hunt as many. “It is believed that bears could catch a couple per month in the fall, compared to 5-10 a month in the spring and early summer,” the researcher clarifies.
According to USGS experts, the most recent polar bear population estimate indicates that it has declined by about 40% in the last decade . However, until now it has been difficult to study the fundamental biology and behavior of polar bears in this remote and hostile environment.
“We now have the technology to learn how they move on the ice, their activity patterns and their energy needs, so that we can better understand the implications of these changes that we are seeing in sea ice,” concludes Pagano.
Reference: AM Pagano el al., “High-energy, high-fat lifestyle challenges an Arctic apex predator, the polar bear,” Science (2018). DOI: 10.1126 / science.aan8677
