Whenever I think of global climate change one of the first images that pops into my mind is that of a polar bear stranded out on a glacier. To me this image alluding to the polar bear’s ‘impending demise’ has in a way become s a rallying point in the fight against global warming. Polar bears always seem to be brought up in conversation when talking about issues that are caused by global warming, yet in the past there’s been little known information about the actual details causing the polar bear’s declining population.
Receding and changing sea ice conditions throughout the Arctic is mostly to blame. However, further details of why that is has been relative limited until fairly recently. Researchers from around the U.S. as part of the U.S. Geological survey, Alaska Science Center, attempted to find out more on these causing mechanisms. By simultaneously measuring a number of factors in polar bears lives including body condition, field metabolic rates, daily activity patterns, and their foraging success, the scientists found high metabolism rates and a deficiency in fat-rich food sources resulted in about half of the bears studied having far less energy intake then they should. For 91% of the polar bears time studied (8-11 days each), the animals were located on sea ice, meaning their food source would come almost entirely from ringed seals. Over a course of 10 to 12 days, 1 ringed seal adult, 3 sub-adult ringed seals, or 19 newborn ringed seal pups are needed simply to break even in energy needed to survive as a freelance bear. However, with reducing amounts of sea ice, scavenging for this food source becomes harder and harder. The researchers observed that 4 of the 9 bears lost over 10% of their fat in the 8-11 days they were observed.
What the researchers also found was that during late spring/early summer time, when the bears are supposed to be gaining weight for the coming winter, polar bears would not be able to reach their goal of 1kg of wight to 1kg of lean body mass (the preferred fatness) unless they either reduced their energy demands or increased food consumption. Yet, these two motives are much easier said then done. The polar bears energy needed for survival is directly correlated with how far the polar bears have to roam around in order to find their next meal. And with the fragmenting sea ice caused by global warming the distance they have to travel increases each year leading to increased amounts of energy being used. The end result, is that these fragmentation’s could be a big factor in the declining body condition and mortality of this species.
Pagano, A. M., et al. 2018. High-energy, high-fat lifestyle challenges an Arctic apex predator, the polar bear. Science Magazine, V. 359(6375): 568-572.