Blog

Are walrus at risk from climate change?

https://www.theguardian.com/environment/2014/oct/03/walrus-alaska-beach-climate-change-arctic-ice

By  Karl Mathiesen @karlmathiesen

Thirty-five thousand walrus on a beach in Alaska, rolling in filth and the carcasses of their kin, have become the unwitting new poster children for climate change.

Within hours of newspapers covering the striking photographs, the walrus and their reason for being on that forlorn shore became enmeshed in the politics of climate change. “This is what climate change looks like,” said WWF. Climate sceptics immediately produced evidence that showed the haul out was nothing out of the ordinary.

Both sides were guilty of simplification. But it is almost certain climate change forced the walrus ashore at Point Lay and it places the species’ future in jeopardy. The walrus, almost all of them females and calves, should be spending their summer on the fringes of the Arctic sea ice. But the ice is gone.

Margaret Williams managing director of WWF’s Arctic programme, said the walrus were the tip of the trophic iceberg.

“The massive concentration of walruses onshore—when they should be scattered broadly in ice-covered waters—is just one example of the impacts of climate change on the distribution of marine species in the Arctic.

“The sharp decline of Arctic sea ice over the last decade means major changes for wildlife and communities alike. These photos are yet another reminder of the urgent need to ratchet down global greenhouse gas emissions—the main human factor driving massive climate change.”

Meanwhile, climate sceptics dug up academic articles that recorded haul-outs of tens of thousands of walrus from as early as the 1978. “Pacific walrus sensationalism – nothing new under the sun,” said the Global Warming Policy Foundation. “The attempts by WWF and others to link this event to global warming is self-serving nonsense that has nothing to do with science.”

This is not a ‘stranding’ in the way that we know it in cetacean terms. The correct term for a mass congregation of walrus is the wonderfully descriptive ‘haul out’.

The important difference is that whales and dolphins are purely aquatic creatures and, unlike walrus, cannot survive on land for extended periods. Strandings of whales and dolphins almost always result in death, whereas walrus haul outs are not inherently unusual.

Kit Kovacs, the biodiversity section leader for the Norwegian Polar Institute and an expert on the mammals that live on and under the Arctic ice, said this particular event was unusual though:.

“Thousands of walrus coming ashore is perfectly normal in Alaska.” But this haul out was significant because it was overwhelmingly females and young. One of the haul outs described in 1978 said that three quarters of the animals were female, but Kovacs said this was “exceptional”.

“It’s always the boys. Before 2006 I am not aware of any mass haul outs that included females on land,” she said.

But in 2006, something strange started happening. Female walrus and their calves started turning up on beaches in Alaska and Russia, first in their thousands, then in their tens of thousands. “A couple of years ago there were sites in Russia where there were 100,000-plus.” This size of congregation, and indeed the Alaskan haul out, is all the more astonishing when you consider the best population estimate for the Pacific walrus subspecies is around 150,000.

Walrus females traditionally spend their summer months nursing newly born calves on the fringes of the sea ice above the shallow waters of the Chukchi Sea.

Their ecosystem is elegant. While the walrus sun themselves above, sunlight filters through the translucent ice sheet. On the underside, algae and microbes breed in tiny crevices and eventually die and fall to the bottom where they become a food source for clams, worms other cephalopods and molluscs. The walrus slide from their icy recline, dive and hoover up the bottom dwellers.

But Arctic sea ice is declining. In terms of the past decade, this year was nothing exceptional – the ice sheet covered 5.09m sq km at its minimum summer extent, considerably larger than two years ago when it fell to its all-time low of less than 3.5m sq km. But this year was still the six lowest on record, more than 1.13m sq km smaller the 1981-2010 average and comes after a decade of decline. Many scientists believe that it is inevitable that the sea ice will eventually disappear completely during the summer months.

Yet for the walrus of the Bering and Chukchi Seas the ice may as well already have disappeared. Kovacs says female walrus began hauling out in Alaska during the summer of 2006 when the ice retreated beyond the continental shelf. Walrus are prodigious divers. They have been recorded plunging to 380 metres. But this is rare and thought to be only used in desperate avoidance of predators. Depths of 80m are the walrus’ usual limit for feeding. But the ice shelf now hovers above deep ocean and the clams are beyond reach.

This change will doubly impact walrus, says Kovacs. In order to find accessible food sources, walrus have flocked to shore. Point Lay is thousands of kilometres from where they would normally be at this time of year. When walrus crowd together in such massive numbers, the threats to life multiply. Any disturbance can cause stampedes that generally kill the young – that’s partly why flight paths were rerouted this week. Disease spreads quickly and the land becomes caked in filth meaning injuries inflicted by stampedes quickly become infected. Photos taken by an Alaskan research team show the suppurating sores on the animals at Point Lay.

Why they swarm, rather than spreading across the landscape more uniformly, is unknown. Kovacs says she has stood on a beach near to a mass haul out and been unable to recognise any difference between it and where the walrus lie in a crowded pile. She suggests it is something to do with their highly social nature and they retain a detailed social memory. Since the industrial persecution of walrus ended in the middle of the 1900s, walrus have been recorded returning to sites that had been abandoned for centuries.

But compounding the effects of the haul outs on the population will be the decline of the ecosystem on which they rely. The walrus will return to the ice as it expands back over the shallow seas, but they may find their food source increasingly scarce.

“Walrus love clams and clams depend on fallout from ice communities,” she says. But with the ice gone from the shallow seas for more and more time each year, the amount of algae dropping down will decrease, potentially causing a collapse in populations on the bottom. “What we are expecting in coming decades is a drop in the carrying capacities [of the sea floor].”

Walrus rely on algae which grows on the bottom of sea ice. They fall to the bottom of the sea feeding the clams that constitute the major food source of the walrus. Photograph: NOAA

The walrus haul out is a highly visible symptom of an ecosystem which appears to already be in an irreversible decline. “It is dramatic,” says Kovacs. “It is extremely likely that it is the direct result of climate change. For Arctic animals, climate change sucks. They are really adapted to the specific conditions.”

And what of the future for the walrus? “We are looking at declining walrus numbers,” Kovacs says. “But extinction? I wouldn’t make that prediction.”

The International Union for the Conservation of Nature says climate change will affect the walrus, particularly those of the Bering and Chukchi seas:

“Although the global population is undoubtedly still quite large, there is evidence of declining populations in two of the subspecies. Climate change is expected to have negative consequences for Walruses, and particularly severe consequences for the Pacific subspecies.”