Loss of Arctic ice forces polar bears to use four times more energy to survive – study | Arctic

Polar bears and narwhals use up to four times the energy to survive due to significant loss of Arctic ice, scientists say.

Once perfectly evolved for polar life, apex predators struggle as their habitats shrink and unique adaptations become less suited to an increasingly ice-free Arctic, the researchers say.

Mammals are physiologically designed to use as little energy as possible. Polar bears are primarily “sit and wait” hunters, adapted to catch seals by breathing holes, and narwhals have evolved to dive very deep in search of prey without making rapid movements. Now, however, they have to work a lot harder to stay alive, according to a review article published in Journal of Experimental Biology.

Polar bears feed primarily on the energy-rich fat of ringed and bearded seals, but this food source is more difficult to find. The sea ice on which they hunt has shrunk by 13% every decade since 1979. Studies show that polar bears now swim for an average of three days to find seals or search for less energy-dense land-based food sources, which forces them to travel further. the distances.

Land resources are unlikely to compensate for the declining feeding opportunities of seals, which means bears are much more vulnerable to starvation. “A polar bear should consume about 1.5 caribou, 37 arctic char, 74 snow geese, 216 snow goose eggs (or 54 nests with four eggs per clutch) or 3 m of blueberries to equal the digestible energy available. in the fat of a banded adult. seal ”, write the researchers in the article.

Narwhals are endurance swimmers that can reach depths of 1,500 meters (5,000 feet) in search of Greenland halibut, their favorite prey. They need reliable breathing holes, but the ice is changing quickly and moving in new ways, which means the holes have moved and in some cases gone.

“The arctic world is so much more unpredictable for these animals now,” said Dr. Terrie Williams, co-author of the report from the Department of Ecology and Evolutionary Biology at the University of California at Santa Cruz. “With a limited amount of oxygen in their muscles and blood, we find that narwhals rate their speed, depth and duration of their dives based on the capacity of their internal scuba tanks. A miscalculation could result in drowning. “

The climate crisis also modifies their migration and opens the arctic regions to industrial activity that encroaches on the territories of narwhals. Killer whales, another major predator, have joined the Arctic marine ecosystem and are known to attack and kill slow narwhals.

The review brings together a number of research papers to better understand how traditional arctic apex predators are likely to decline. “We wanted to sort of summarize what we know about the physiology of these animals… we really saw a lot of similarities between them,” said Dr Anthony Pagano, co-author of the zoo’s Conservation Research Institute. from San Diego.

The decline of polar bears and narwhals is likely to have a ripple effect on other ice-dependent mammals and their prey, leading to “rapid changes throughout the Arctic marine ecosystem,” according to Researchers. Mammals like beluga whales, arctic foxes, and muskoxen are likely to be vulnerable to similar changes.

The paper corroborates existing models that predict an overall decline in polar bear abundance of between one and two thirds by the end of the century. “We need to reduce our carbon footprint by using all the human ingenuity we can muster. If for no other reason that a world without polar bears and narwhals would be a sadder place, ”said Williams.

Professor Klaus Dodds of the Geography Department at Royal Holloway, University of London, who was not involved in the study, said it was an important article. “As the Arctic continues to burn, melt and thaw, a cascade of shocks and reverberations will continue to occur.

“Iconic species such as polar bears, seals and whales are vulnerable to changes in the distribution and thickness of sea ice. As marine ecologies change shape, mammals are perfectly adapted to an environment. reliably frozen will find it difficult to adapt. The cost of current and future adaptation will be high. “

Professor Steve Albon, Honorary Research Associate at the James Hutton Institute, who was not involved in the research, said: “By calculating the energy costs of sea ice loss for these predators, we can predict the likely consequences. for their reproduction and survival. long before we have proof of their decline. “