The Heat Is On

Is climate change causing the arctic food chain to unravel?

By Sharon Oosthoek

© Thomas Mangelsen / Minden Pictures

© Thomas Mangelsen / Minden Pictures





But now that some killer whales are making Hudson Bay their summer home, scientists wonder what it means for the food web. Stable isotope analysis of the teeth of two orcas found in the bay suggests they are eating narwhals, belugas and bowheads. With little experience evading killer whales, and no ice in which to hide, these marine creatures could be in trouble. To make matters more complicated, both predator and prey are at-risk species in this part of the world. “We’re not confident these [prey] populations can adapt,” says Ferguson. “They’re not likely to say, ‘Let’s move out of Hudson Bay. It’s not a safe place anymore.’” 

The whales’ presence in Hudson Bay is but one example of the proverbial canary in a coal mine. It illustrates the complexity of climate change’s impact in the far north, including Alaska. Across the region, species are moving and interacting in brand new ways and causing the food web to unravel. 

Certainly Alaska is heating up faster than anywhere else in the United States. Over the past 50 years, the northernmost state has seen some of the most rapid warming on Earth, with temperatures rising 1 to almost 4 degrees Fahrenheit. As with Hudson Bay’s killer whales, warming temperatures mean an expanded range for some northwestern and Alaskan species, potentially putting others at risk. 

The U.S. Fish and Wildlife Service, for example, reports that the northward expansion of beavers has blocked many traditional salmon-spawning streams. New research also suggests increased competition between trumpeter swans and tundra swans—on whose territory the trumpeters are now encroaching. 

National Park Service biologist Joshua Schmidt, along with colleagues from the National Ocean and Atmospheric Administration and the University of Alaska, analyzed trumpeter swan breeding range data from 1968 to 2005. Their study, published in the journal Wildlife Biology in 2011, found trumpeters have expanded their ranges north as the number of above-freezing days at higher latitudes has increased. 

But because their smaller cousins, the tundra swans, already breed at these latitudes, the move brings the two species into direct competition. Under the former climate regime, length of their respective breeding seasons likely kept them apart—trumpeter swans require up to 45 more days above freezing than do tundra swans. Scientists don’t know yet whether the larger swan’s presence at higher latitudes is affecting populations of tundra swans, but Schmidt and his colleagues suggest it could be bad news for the smaller birds. 

A shift in breeding range also plagues Alaska’s walruses. Walrus mothers off the northwest coast usually stay with the Chukchi Sea ice as it retreats north for the summer. That’s because there are fewer predators on ice than on land, making it a good place to haul out to give birth and nurse their young. And when it’s time to eat, mothers can dive to the shallow ocean floor for clams. 

“But the sea ice is retreating earlier and farther north into the Chukchi each summer,” says Karla Dutton, Defenders’ Alaska director. In four out of the past five summers, it has disappeared from above the clam-rich continental shelf and instead floats over the deep ocean where clams are few and far between. When that happens, walruses abandon the summer sea ice, opting instead to haul out on land, closer to their feeding grounds. But the consequences are proving deadly. 

When walruses gather on chunks of sea ice they usually number 50 or fewer individuals. On land, herds can reach into the tens of thousands. “So if there is any disturbance from humans or bears or airplanes or boats, they will stampede to the water and trample calves,” says United States Geological Survey (USGS) marine biologist Chad Jay. In 2009, USGS scientists counted 130 dead walruses—mostly calves—after one trampling incident off the northwest coast of Alaska. 

Walruses are too big to ignore when their behavior changes so dramatically, but it seems even the tiniest northern organisms are feeling the heat. Scientists recently discovered thinner summer sea ice in the Chukchi Sea is responsible for massive phytoplankton blooms, which form the base of the Arctic food chain.  

Writing in the journal Science last June, Stanford University marine scientist Kevin Arrigo and colleagues showed that as the ice melts, it forms pools of water on top that concentrate sunlight down below. The extra light triggers phytoplankton blooms, making these areas more productive. 

The researchers now worry that an earlier Arctic spring may mean earlier sea ice melt and earlier phytoplankton blooms. That could spell trouble for migrating marine animals that arrive looking for food after the blooms’ peak. 

Of course, any change in environment has the potential to produce winners and losers, says Brendan Kelly, assistant director for polar science in the Executive Office of the President.

He points to humpback whales which are moving farther north to feed. “The increased access to formerly inaccessible waters likely will benefit their populations,” says Kelly. “On the other hand, the potential impact on bowhead whales competing with humpbacks might be a net negative for the bowheads.” 

A warming north is also making for some strange cross-species bedfellows. 

In 2010, Kelly was part of a group of wildlife experts who sounded an alarm about the suspected link between rising temperatures and the hybridization of northern wildlife. Writing in the journal Nature, Kelly and his co-authors pointed to grizzly-polar bear hybrids in Canada’s north, suggesting they are a sign of Arctic biodiversity at risk. They argue governments must manage hybrids before interbreeding leads to the extinction of rare species. 

In April 2006, Idaho hunter Jim Martell shot the first genetically confirmed “grizzlar” in the Northwest Territories. Martell thought he’d shot a polar bear, but when he and his Inuit guide, Roger Kuptana, got closer they discovered the creature had unusual features. Its white fur was mottled with brown patches, and thin circles of black skin rimmed its eyes. It also sported the grizzly’s distinctive long claws and humped back. 

British Columbia-based wildlife geneticist David Paetkau, whose company tested the hybrid’s DNA, muses that warming temperatures may be causing shorter hibernation periods for grizzlies. With more time on their paws, grizzly males may now be wandering north, where they’re mating with polar bears. Several other grizzlars have since been spotted in Canada’s north and it’s possible they exist in Alaska, too. 

Meanwhile, Kelly suggests the resulting hybrids may have a leg up initially, but that each mixing of species could bring bad news in terms of their ability to adapt. The genetic gamble certainly had mixed results for polar-grizzly hybrids in a German zoo. They were good at hunting seals, but didn’t have the strong swimming abilities of their polar bear forebears. 

“In a first generation you retain most of the good qualities of each of your parent species,” says Kelly. “But over time, you will break up those combinations more and more. You’ll get more maladaptive combinations. So the good news [for the hybrid bear] is, ‘I’ve got these great sealing abilities, the bad news is that I really can’t swim.’” 

This impacts more than just the polar bear. “If hybrid polar bears lose their ability to stalk and kill ringed and bearded seals, their primary prey, species like arctic fox will be in dire straits as they rely on polar bears to provide the bulk of their winter diet from the remains of seals killed for their blubber,” adds Defenders’ Dutton.

Of course bears are not the only animals capable of crossbreeding under warming conditions. Rapidly disappearing sea ice means the barrier that once kept Arctic species apart is literally melting away. Kelly and his co-authors also point to an apparent bowhead-right whale photographed in the Bering Sea in 2009, a suspected narwhal-beluga found west of Greenland in the late 1980s, as well as various confirmed hybrid porpoises and seals. 

University of Alaska marine biologist and co-author, David Tallmon says that while it’s unlikely hybridization is widespread in the Arctic, no one has looked systemically at the issue. 

“It’s likely to become increasingly important as the summer ice diminishes and is ultimately lost,” says Tallmon. “Hybridization is essentially impossible to reverse once it has begun on a large scale. So, we want to be sure to halt any hybridization before it becomes unmanageable and unique lineages are lost forever.” 

While the situation for some northern species may be dire, good science is crucial when finding solutions, researchers point out. That’s why Defenders of Wildlife helped launch USGS’s Climate Change and Wildlife Center and lobbies to keep it funded every year. With the opening of a new office in Alaska, scientists will be able to focus on northern species. 

Defenders is also championing the development of The National Fish, Wildlife and Plants Climate Adaptation Strategy. It represents an unprecedented cooperative effort among federal, state and tribal partners to put forth a plan to safeguard fish, wildlife, plants and the natural systems on which they depend. 

In the meantime, it’s important to know that there will in fact be successful adaptations to climate change, says Kelly. The key though is that the ability to adapt is all about the pace of change. “Changes that happen over one or a few generations are more likely to lead to population reductions and extinctions than will slower changes that span more generations,” says Kelly. “It is not too late to reduce emissions of greenhouse gases that are driving changes in the Arctic ecosystem.” 

Toronto journalist Sharon Oosthoek’s story about black-footed ferrets and prairie dogs ran in the winter 2011 issue of Defenders.

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