By BRUCE BARCOTT, OnEarth magazine
Biologists studying polar bears off the coast of Alaska have discovered that when cubs are pressured to go on marathon swims with their moms as a consequence of loss of sea ice, practically half of them do not survive to develop into yearlings.
The examine, scheduled to be introduced on the International Bear Association Conference in Ottawa on Tuesday, confirms the risks of ice loss to Alaska’s polar bear inhabitants. It has been broadly theorized that grownup polar bears have been pressured to cross ever-longer stretches of open ocean because the polar areas warmth up.
The brand new work, by U.S. Geological Survey Alaska Science Center researchers Anthony Pagano, Kristin Simac, George Durner, and Geoff York, confirms that idea. It additionally reveals that these open-water swims have a dramatic impact on younger cubs, that are pressured to observe their moms seeking meals and strong floor.
“This analysis is the primary evaluation to determine a big multi-year pattern of elevated long-distance swimming by polar bears,” co-author Geoff York stated Monday. “Local weather change is pulling the ocean ice out from beneath polar bears’ ft, forcing some to swim longer distances to search out meals and habitat.”
“We discovered that grownup females with cubs, who undertook lengthy distance swims, had been 1.6 instances extra more likely to be with out these younger throughout a subsequent reobservation than females that didn’t swim,” added George Durner, York’s co-author. The researchers don’t know for sure that the cubs drowned, or died as a consequence of causes associated or unrelated to the prolonged swim. “However what our information suggests is that there could also be a relationship between cub mortality and lengthy distance swimming,” Durner wrote in an e-mail.
The info that led to these findings was a little bit of a shock. “This got here to us purely by chance,” stated York, who labored for the USGS in Alaska from 1996 to 2008. His work there was vital within the U.S. Fish & Wildlife Service’s 2008 resolution to list polar bears as threatened beneath the Endangered Species Act. (York is now an Arctic species specialist for the World Wildlife Fund.)
Each spring, USGS researchers catch and collar grownup feminine polar bears within the Beaufort Sea and Chukchi Sea and observe their actions by way of GPS monitoring. “Due to their physique form, the collars simply don¹t keep on the males,” York stated. “And it is too harmful to collar younger sub-adults as a result of they develop too rapidly. The collar may develop into a choking hazard. A lot of what we all know is predicated on the motion of feminine bears — the place the ladies are.”
In 2004, a brand new kind of collar started working erratically. “We had been getting these unexplained gaps in transmission,” York recalled. “I took these gaps and overlaid them on maps of sea ice protection.” There appeared to be a correlation between gaps in every bear’s observe and the lack of sea ice.
That is when the scientists realized that the brand new collars occurred to be designed with the GPS transmitter on the decrease half of the collar, which submerged when the bears had been swimming. Water blocked the sign — therefore the information gaps (a idea they later confirmed with new know-how).
Pagano and York collected information from 68 GPS collars over a six-year stretch from 2004 by way of 2009. Every collar has a battery that lasts a couple of 12 months, and is programmed to unlock and fall off close to the tip of the battery’s life. They checked out every mom bear’s swimming file and located 50 long-distance swimming occasions (greater than 30 miles) involving 20 bears over these six years. One bear swam 426 miles. One other was in open water for practically 13 straight days.
Eleven bears that swam lengthy distances had younger cubs on the time of the collar deployment. 5 of these bears misplaced their cubs in some unspecified time in the future through the examine 12 months, a 45 p.c mortality charge. Amongst cubs not compelled to swim lengthy distances, the mortality charge was 18 p.c.
“Grownup polar bears are sturdy swimmers,” York stated. “However they cannot maintain their noses whereas swimming, in order that they’re in danger for drowning if a storm hits. Cubs are at even higher danger. Their smaller physique measurement leaves them extra susceptible to hypothermia, they usually do not have the vitality reserves of the grownup bear. They can not feed whereas swimming, and it takes a whole lot of vitality to maintain up with mother.”
This June, much less sea ice lined the Arctic than in any 12 months, save one, since information started being stored in 1979. And due to heavy melting in July, the National Snow and Ice Center in Boulder, Colo., stories that 2011 is now on observe to drop under the file low-ice minimal set in 2007.
Arctic sea ice normally reaches its lowest level through the first week of September, which suggests these cubs could also be doing much more swimming this summer season.
Bruce Barcott wrote this article for OnEarth Magazine. He’s a 2009 Guggenheim Fellow in nonfiction, is the writer of ‘The Final Flight of the Scarlet Macaw,’ named among the finest books of 2008 by Library Journal, and ‘The Measure of a Mountain: Magnificence and Terror on Mount Rainier.’