Harp Seal Population Threatened By Melting Atlantic Ice
January 5, 2012

Harp Seal Population Threatened By Melting Atlantic Ice

Warming in the North Atlantic Ocean has lead to "significantly reduced" sea ice levels in the breeding grounds of harp seals over the past three decades, Duke University researchers have discovered.

Harp seals, which according to BBC News Environment Correspondent Richard Black are "doe-eyed animals" that are "the prime target for Canada's annual seal hunt," have experienced an approximately 6% per decade decrease over the past 30-plus years, the scientists have claimed.

"The kind of mortality we're seeing in eastern Canada is dramatic," David W. Johnston, a research scientist at the university's Marine Lab, said in a statement Wednesday. "Entire year-classes may be disappearing from the population in low ice years — essentially all of the pups die.

"It calls into question the resilience of the population," he added. "As a species, they're well suited to deal with natural short-term shifts in climate, but our research suggests they may not be well adapted to absorb the effects of short-term variability combined with longer-term climate change and other human influences such as hunting and by-catch."

According to Johnston, harp seals are dependent on wintertime sea ice as safe-havens -- places where they can give birth to, nurse, and raise pups until the younger members of the population are old enough to hunt and swim on their own. Typically, he says, female seals search for the oldest and thickest ice sheets each February and/or March, and have been forced to adapt to warmer conditions by reducing nursing periods to a brief 12-day span.

Black reports that the most important breeding zone for these seals is along the Gulf of St. Lawrence on the eastern coast of Canada. The region extends northward along a region off Newfoundland known as the Front. In 2007, the Canadian government reported that poor ice conditions in the southern part of the gulf resulted in an "extremely high" mortality rate among the harp seal population.

"The Duke researchers were able to show that mortality of seal pups, as measured by strandings, has historically varied with February and March sea ice extent as measured by satellite," the BBC News reporter said. "It has also varied with the North Atlantic Oscillation (NAO), a naturally occurring climate cycle - which makes intuitive sense as the NAO also affects ice."

"Opposite phases of the NAO alternately benefit either the Canadian or Russian populations" of harp seals, he added. "Genetic studies indicate some mixing between the two, indicating that some of the seals can move between the breeding grounds“¦ And recently, scientists have reported seeing breeding groups on coastal ice around areas of Greenland where they have not traditionally bred, which may indicate a capacity to move northwards as the overall climate of the sub-Arctic warms up."

However, the question of whether or not the seals will be able to respond to the warming trend by relocating to other, more stable ice habitats, on a long-term basis, the university noted in a January 4 press release. The findings of the Duke study were published Wednesday in the journal PLoS One.


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