Science & Technology

Polar Bears Skinnier & Having Fewer Cubs Due to Less Sea Ice in Baffin Bay

A polar bear in Baffin Bay, West Greenland in 2012 seen from the air. Credit score: Kristin Laidre/College of Washington

Polar bears are spending extra time on land than they did in the Nineties due to lowered sea ice, new College of Washington-led analysis exhibits. Bears in Baffin Bay are getting thinner and grownup females are having fewer cubs than when sea ice was extra out there.

The brand new research, not too long ago printed in Ecological Purposes, contains satellite tv for pc monitoring and visible monitoring of polar bears in the Nineties in contrast with newer years.

“Local weather-induced modifications in the Arctic are clearly affecting polar bears,” mentioned lead writer Kristin Laidre, a UW affiliate professor of aquatic and fishery sciences. “They’re an icon of local weather change, however they’re additionally an early indicator of local weather change as a result of they’re so depending on sea ice.”

The worldwide analysis crew centered on a subpopulation of polar bears round Baffin Bay, the massive expanse of ocean between northeastern Canada and Greenland. The crew tracked grownup feminine polar bears’ actions and assessed litter sizes and the overall well being of this subpopulation between the Nineties and the interval from 2009 to 2015.

The research in contrast the actions of grownup feminine polar bears throughout two time intervals. Within the Nineties (left), sea ice in mid-July nonetheless spanned Baffin Bay, offering polar bears with a big space to hunt and journey. In newer summers (proper), Baffin Bay was largely open water in mid-July, and polar bears have been caught nearer to shore. Credit score: Joshua Stevens, NASA Earth Observatory/Nationwide Snow & Ice Information Heart

Polar bears’ actions usually comply with the annual progress and retreat of sea ice. In early fall, when sea ice is at its minimal, these bears find yourself on Baffin Island, on the west facet of the bay. They wait on land till winter after they can enterprise out once more onto the ocean ice.

When Baffin Bay is roofed in ice, the bears use the strong floor as a platform for searching seals, their most popular prey, to journey and even to create snow dens for his or her younger.

“These bears inhabit a seasonal ice zone, that means the ocean ice clears out fully in summer time and it’s open water,” Laidre mentioned. “Bears in this space give us a great foundation for understanding the implications of sea ice loss.”

Satellite tv for pc tags that tracked the bears’ actions present that polar bears spent a mean of 30 extra days on land in latest years in contrast to in the Nineties. The common in the Nineties was 60 days, usually between late August and mid-October, in contrast with 90 days spent on land in the 2000s. That’s as a result of Baffin Bay sea ice retreats earlier in the summer time and the sting is nearer to shore, with newer summers having extra open water.

The authors in contrast the actions of 43 grownup feminine polar bears with tags that recorded their positions from 1991 to 1997 (left) with these of 38 grownup females tracked from 2009 to 2015 (proper). With much less sea ice, the bears’ actions are restricted to a smaller space and so they spend extra time shut to shore, particularly in Greenland. Credit score: Joshua Stevens/NASA Earth Observatory and Kristin Laidre/Uiversity of Washington

“When the bears are on land, they don’t hunt seals and as a substitute depend on fats shops,” mentioned Laidre. “They’ve the power to quick for prolonged intervals, however over time they get thinner.”

To evaluate the females’ well being, the researchers quantified the situation of bears by assessing their degree of fatness after sedating them, or inspecting them visually from the air. Researchers categorised fatness on a scale of 1 to 5. The outcomes confirmed the bears’ physique situation was linked with sea ice availability in the present and former 12 months — following years with extra open water, the polar bears have been thinner.

The physique situation of the moms and sea ice availability additionally affected what number of cubs have been born in a litter. The researchers discovered bigger litter sizes when the moms have been in a great physique situation and when spring breakup occurred later in the 12 months — that means bears had extra time on the ocean ice in spring to discover meals.

The authors additionally used mathematical fashions to forecast the way forward for the Baffin Bay polar bears. The fashions took into consideration the connection between sea ice availability and the bears’ physique fats and variable litter sizes. The conventional litter dimension could lower inside the subsequent three polar bear generations, they discovered, primarily due to a projected persevering with sea ice decline throughout that 37-year interval.

“We present that two-cub litters — normally the norm for a wholesome grownup feminine — are possible to disappear in Baffin Bay in the following few a long time if sea ice loss continues,” Laidre mentioned. “This has not been documented earlier than.”

Laidre research how local weather change is affecting polar bears and different marine mammals in the Arctic. She led a 2016 research displaying that polar bears throughout the Arctic have much less entry to sea ice than they did 40 years in the past, that means much less entry to their essential meals supply and their most popular den websites. The brand new research makes use of direct observations to hyperlink the lack of sea ice to the bears’ well being and reproductive success.

“This work simply provides to the rising physique of proof that lack of sea ice has critical, long-term conservation issues for this species,” Laidre mentioned. “Solely human motion on local weather change can do something to flip this round.”

Reference: “Interrelated ecological impacts of local weather change on an apex predator” by Kristin L. Laidre, Stephen Atkinson, Eric V. Regehr, Harry L. Stern, Erik W. Born, Øystein Wiig, Nicholas J. Lunn and Markus Dyck, 10 January 2020, Ecological Purposes.
DOI: 10.1002/eap.2071

Co-authors of the research are Eric Regehr and Harry Stern on the UW; Stephen Atkinson and Markus Dyck on the Authorities of Nunavut in Canada; Erik Born on the Greenland Institute of Pure Sources; Øystein Wiig on the Pure Historical past Museum in Norway; and Nicholas Lunn of Atmosphere and Local weather Change Canada. Foremost funders of the analysis embrace NASA and the governments of Nunavut, Canada, Greenland, Denmark, and the USA.
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