Arctic snowfall accumulation plays a critical role in ringed seal breeding, but may be at risk due to climate change, according to a new study in Geophysical Research Letters. Sea ice, which is disappearing at an alarming rate, provides a crucial platform for the deep snow seals need to reproduce.
Ringed seals (Phoca hispida) require snow depths of at least 20 centimeters (8 inches): deep enough to form drifts that seals use as birth chambers.
Ringed seals rear their young in April, which also makes the timing of adequate snow depths critical.
“Depending on how fast greenhouse gases increase this century, the area of Arctic sea ice with at least 20 centimeters of snow in April could decrease by nearly 70 percent,” co-author Cecilia Bitz, associate professor of atmospheric sciences at the University of Washington, told mongabay.com.
Ringed seal (Phoca hispida). Photo by: NOAA.
Sea ice reduction through autumn could be particularly perilous to future seal populations.
“Cumulative snowfall changes little from September to April during the 21st century in climate model projections. However, the projected loss of sea ice in autumn causes early season snowfall to fall into the ocean,” said Bitz, adding “it is the loss of the sea ice platform to catch the snowfall that causes snow depths to decrease in the future”.
Ringed seals are unable to build caves deep enough if insufficient snow is available. In fact, scientists have found that seal pup survival diminishes in locations without at least 20 centimeters of snow on level sea ice in April, increasing pup mortality through exposure (and the threat of freezing) and predation.
Seal caves may be threatened by other features of climate change too. For example, warmer temperatures mean that caves could melt sooner, affecting the time needed for pups to mature.
Increased precipitation as rain is another factor according to Bitz.
Ringed seal pup. Photo by: NOAA.
“Rainfall rates will roughly double by the end of the 21st century and rain falling on snow caves can cause them to collapse,” she notes, adding that “rain falling on sea ice can also accelerate snow and ice melt rates. Higher rates of rainfall are a further pressure on seal habitat”.
The findings could also have major implications for other Arctic species that depend on ringed seal populations.
“Ringed and bearded seals are the most common food for polar bears. They are adept at hunting seals, and seals have enough fat to satisfy their energy needs,” says Bitz.
Scientists have long recognized that climate change imperils Arctic species such as polar bears (Ursus maritimus), Arctic foxes (Alopex lagopus), killer whales (Orcinus orca) and even glaucous gulls (Larus hyperboreus). Now, their existence could be challenged further, by the potential plight of an important prey species.
A decline in ringed seals would also hurt another top predator: humans. Ringed seals are extremely important for the Arctic’s indigenous human populations. Widely hunted across Arctic regions, ringed seal meat is central to many indigenous diets while their skins are used for warm clothing in the frigid climate.
Ringed seal hides have been used by indigenous people for millennia as clothing. Photo by: Mickey Bohnacker.
Not only are ringed seals prized for the practical benefits they deliver, they are also culturally and socially significant for indigenous populations across the expanse of the Arctic.
Ringed seals are currently listed as Least Concern by the IUCN. In 2010, the National Oceanic and Atmospheric Administration (NOAA) proposed (together with growing evidence) that both ringed and bearded seals be listed as ‘Threatened’ under the Endangered Species Act (ESA); however the decision is still under consideration.
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87 marine mammals still eaten by people
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