The gathering of 35,000 walrus on a beach in northwest Alaska this week after they couldn’t find their preferred resting grounds of summer sea ice was a notable occurrence in terms of its sheer size, but it wasn’t an isolated event.
Walrus have been gathering on Alaska’s shore in huge numbers almost every year since 2007, a relatively new phenomenon that has scientists working to determine how this change in resting grounds affects the walrus’ behavior, food supply, and health. Typically, Pacific walrus, which don’t have the stamina to swim indefinitely and depend on sea ice for places to rest periodically, follow sea ice in the Bering Sea as it recedes north in the summer, ending up in the Chukchi Sea off the coast of Alaska. This year — and every year since 2007 besides 2008, when there was just enough sea ice left for the walrus to make use of — all the summer sea ice disappeared, causing a record 35,000 walrus to convene on an Alaska beach.
Tony Fischbach is a wildlife biologist with the U.S. Geological Survey who’s a member of the Walrus Research Program in Anchorage, Alaska. He told ThinkProgress that when summer sea ice is at normal levels, only a small number of walrus will come to shore in Alaska — numbers typically in the tens or sometimes low hundreds of animals. This mass convergence of walrus — most of whom are females and calves — is a new phenomenon, he said.
“Under historical conditions, there has always been sea ice over the Chukchi Sea over the summer,” he said. “This is a real change that we see thousands and tens of thousands of animals coming to shore and resting together in these large haul-outs.”
There are always concerns about disease transmission when large numbers of animals convene, Fischbach said, but in past years disease hasn’t caused problems. Trampling is also a concern in groups this large — in past years, more than 100 calves have died in Alaska due to trampling, and in Russia, more than 1,000 have died. Fischbach said he doesn’t foresee trampling being a major problem this year, however, despite the fact that some dead walruses have already been discovered.
But besides these immediate concerns on the lives and health of these creatures, the major haul-outs represent a change in behavior that leads to questions as to how walrus will adapt to shrinking sea ice levels.
“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,” Margaret Williams, managing director of the World Wildlife Fund’s Arctic program, said.
Walrus wait until sea ice starts forming again to start their fall migration south. That usually puts the start of their fall migration around mid-September, but this year’s lack of sea ice — and the subsequent stopover of the walrus in Alaska — is delaying their migration, Fisbach said. That probably won’t result in any mismatches in food availability when they reach their destination, Fisbach said, since the mollusks and benthic creatures such as worms, crustaceans and sea cucumbers that they feed on are available year-round, but it’s still a break from the norm.
CREDIT: National Snow and Ice Data Center
Under normal conditions, during their fall migration, walrus rest briefly on sea ice before returning to the sea to forage for food and continue on their way South. But Fisbach said that these huge groups of walrus can remain on the Alaska shore for three to five weeks at a time, with individual walrus entering the sea to forage and returning to the beach to rest periodically. Fisbach said this behavior raises “lots of questions” about whether the walrus will run out of food in the surrounding area, due to the high numbers of walrus competing for food.
“Occupying these areas and foraging these areas concentrates tens of thousands of walruses in a smaller area that is already known to be less rich than their off-shore foraging ground, and there is a concern that they could deplete the resources,” he said. “We don’t have a good measure of that — these are simply hypotheses or concerns we have.”
Some of the 35,000 walrus have been taking long trips offshore to forage, Fisbach said, while others have been sticking close to shore. Journeying farther out to sea may grant the walrus access to better food supplies, but it could also mean that they’re expending more calories than they’re gaining, Fischbach said. He’s working on a project that involves attaching radio tracking devices to the walrus so that he can track their behavior in the group — where and how often they go to forage and how often they rest — and compare it to historical data on walrus behavior.
Fischbach also said that, despite the fact that the walrus have convened on the shores of Alaska and Russia for the past several ice-free summers, he isn’t certain that the walrus will continue to gather in large numbers in the same places.
“For us, it really appears that this is a new phenomenon for walruses. How they respond in the long term is an open question,” he said. “Will they continue to have this pattern of coming to shore [and] being aggregated in a large group in the future, or will they deplete the local forage areas and choose other areas to rest? We don’t know…they’re wild animals and they’re responding to many factors we aren’t able to perceive.”
Loss of sea ice in the Pacific walrus’ range has led to calls to put the species on the Endangered Species List. The current population of the species is estimated at more than 200,000 individuals, but as the earth continues to warm and sea ice continues to retreat, some are worried that walrus populations will take a hit.