Many signs of melting sea ice, visible from satellites, airplanes, and ships, tell us that polar bears are threatened by climate change. Researchers from the University of Alberta have added another dimension to the calculations of survival of bear populations, which will measure signs that are not readily available to the eye.

Peter Molnar, of the university’s Centre for Mathematical Biology, and university professors Andrew Derocher and Mark Lewis, used mathematical modeling to show that polar bear populations could plummet if ice-free periods in the Arctic continue to increase.

According to a university news release, they assigned numerical values to study how long the 900 male polar bears living near Churchill, Manitoba, can go without food when they’re cut off from their hunting grounds on the sea ice of Hudson Bay. The researchers had data on the weight and energy-storing capacity of polar bears, and they knew that the ice-free period had increased by three weeks over the last 30 years.

Derocher said, “If the ice-free period extends to 180 days, our modeling shows upward of half of those animals will die.” Now ice-free periods in the bay vary from 90 to 135 days.

In addition, the changes in sea ice and the extended periods without of fasting could happen quickly, according to the researchers. The result would be landlocked and hungry bears in the town of Churchill, as well as sudden decline in the number of bears. 

The mathematical models also show that the age-old system of finding mates by tracking is endangered when the sea ice breaks up. The researchers concluded the pregnancy rate could drop by 30 percent.

“We have two thirds of the world’s polar bears and collectively scientists around the world and people are looking to Canada for leadership but we’ve been very slow to recognize polar bears as a threatened species,” said Derocher. “That has to change.”

The work of Molnar, Derocher and their colleagues is published in the July issue of Biological Conservation – Predicting survival, reproduction and abundance of polar bears under climate change