Scientists say polar bears and narwhals use up to four times the energy to survive due to massive ice loss in the Arctic.
Once perfectly evolved for polar life, apex predators struggle as their habitats shrink and unique adaptations become less suitable for an increasingly ice-free Arctic, researchers say.
The 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 much harder to stay alive, according to a review article in the Journal of Experimental Biology.
Polar bears mainly feed on the energy-rich mud of ring and bearded seals, but this food source is more difficult to find. The sea ice they hunt has shrunk by 13% every decade since 1979. Studies show that polar bears now swim an average of three days to find seals, or search for less energy-dense terrestrial food sources, forcing them to travel further. distances.
Land-based resources are unlikely to compensate for the decline in seal feeding opportunities, meaning the bears are significantly more vulnerable to hunger. “A polar bear should consume about 1.5 caribou, 37 Arctic char, 74 snow geese, 216 snow geese eggs (ie 54 nests with four eggs per clutch) or 3 meters of crows to match the digestible energy available in an adult’s mud. ringed seal, ”researchers write in the newspaper
Narwhals are endurance swimmers who 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 rapidly changing and moving in new ways, meaning holes have shifted and in some cases disappeared.
“The polar world is now so much more unpredictable for these animals,” said Dr. Terrie Williams, a co-author of the report from the Department of Ecology and Evolutionary Biology at the University of California, Santa Cruz. “With a limited amount of oxygen in their muscles and blood, we see the narwhals adapt their speed, depth and duration of dives to the capacity of their internal diving tanks. Incorrect calculation can lead to drowning. “
The climate crisis is also changing their migration and opening the Arctic regions to industrial activity that encroaches on narwhal areas. Killer whales, another apex predator, have joined the marine Arctic ecosystem and are known to attack and kill slow-moving narwhals.
The review collects a number of research papers to better understand how the Arctic’s traditional apex predators are likely to decline. “We wanted to summarize a little bit what we know about the physiology of those animals … we really saw a lot of similarities between them,” said Dr. Anthony Pagano, a co-author of the Institute for Conservation Research at San Diego Zoo Global.
The decline of polar bears and narwhals is likely to have a knock-on effect on other ice-dependent mammals and their prey, leading to “rapid changes throughout the Arctic marine ecosystem,” say researchers. Mammals such as beluga whales, arctic foxes and musk oxen are likely vulnerable to similar changes.
The article confirms existing models predicting a worldwide decline in polar bear numbers by a third to two thirds by the end of the century. “We have to reduce our ecological footprint by using everything we can. If for no other reason than a world without polar bears and narwhals it were a sadder place, ”said Williams.
Prof Klaus Dodds, of the Royal Holloway, University of London geography department, 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 exist.
“Iconic species such as the polar bear, seal and whale are vulnerable to changes in the distribution and thickness of the sea ice. As marine ecologies change shape, perfectly adapted mammals to a reliably frozen environment will struggle to adapt. The costs of current and future adjustments will be high. “
Prof Steve Albon, an honorary research associate at the James Hutton Institute, who was not involved in the study, said, “By calculating the energetic costs of sea ice loss to these predators, we can determine the likely effects on their reproduction. and predict survival. long before we have proof of their declining numbers. “