35,000 walruses are swarming Alaska's shore — because their sea ice is vanishing

Pacific walruses have long relied on floating sea ice in the Arctic. They use it as a resting place between dives as they forage for shrimp, worms, and mollusks on the ocean floor. Female walruses also give birth on these ice platforms and raise their pups there.

As the sea ice recedes, walruses are hauling out on land instead

But thanks to global warming, all that Arctic sea ice is dwindling. And so, in recent summers, many walruses have been seeking refuge on the northern shores of Alaska and Russia instead.

This September, scientists observed one of the biggest land haul-outs in recent memory in northern Alaska — with an estimated 35,000 walruses crowding the shore of a remote barrier island near Pt. Lay. Surveyors from the National Oceanic and Atmospheric Administration photographed the event on September 13 during their annual aerial survey of Arctic marine mammals:

(Corey Arrardo / NOAA/NMFS/AFSC/NMML)

This sort of behavior is hardly unprecedented — walruses do clamber up on land now and again for rest. But, up until recently, scientists say, it was unusual to see so many walruses on shore for such a prolonged period of time.

Typically, during the summer months, female walruses and their calves will stay with the sea ice as it recedes north, past Alaska. There, the walruses will use the ice as a platform to hunt for food in the relatively shallow waters of the Chukchi Sea. Then, when the ice grows again in the winter, the walruses migrate south along with it.

But if the ice recedes too far north in the summer — into deeper waters and away from the feeding grounds — then more and more walruses have to abandon the ice and swim toward land. That's what happened this year: September 2014 saw the sixth-smallest sea-ice extent on record, with the ice north of Alaska and eastern Siberia pulling further back than it has historically:

(National Oceanic and Atmospheric Administration)

This seems to be an increasingly common occurrence, and the US Geological Survey has blamed it on climate change.

Major walrus haul-outs have now been observed in Alaska in six of the past eight years — at a time when Arctic sea ice has been shrinking. In 2010, some 20,000 walruses came ashore near Pt. Lay. In 2011, nearly 30,000 came ashore. (You can watch a video of that one here.) In 2013, another 10,000 came ashore.

(In Russia, meanwhile, scientists have said that they first observed massive walrus herds stay onshore for extended periods of time in the late 1990s — before then, it was a much, much rarer sight.)

The haul-out on September 13 of this year appears to be one of the largest ever observed in northern Alaska, though NOAA is still trying to verify the exact numbers. By the end of the month, there were still a few thousand walruses remaining onshore in the area, and the FAA was trying to re-route flights over the area so as to avoid a stampede.

Can walruses adapt to a lack of sea ice?

That's a question scientists are still trying to figure out.

There's at least one potential danger in these land haul-outs: young walrus pups are somewhat more likely to be trampled when they're onshore, particularly if the walruses are spooked by a polar bear or humans and start stampeding. (This happened back in 2007 after some 40,000 walruses appeared on the shores of northern Russia; thousands died in a stampede.)

(Corey Arrardo / NOAA/NMFS/AFSC/NMML)

So far, there don't appear to be any major problems with this walrus haul-out in Alaska. A researcher with the US Geological Survey told the Anchorage Daily News that 50 dead walruses were spotted at Pt. Lay last week, and another 36 this week, but scientists still need to do autopsies to determine the exact cause of death.

Researchers have also pointed out that these beaches are often remote from the best feeding spots, which means that the walruses may have to expend more energy to forage for food if they're stranded ashore. The US Geological Survey is currently tagging and tracking walruses to see if this affects their ability to store fat at all. (There's a similar concern with polar bears in the region, which also have to swim even longer distances for food as sea ice recedes.)

How dwindling sea ice will ultimately affect walruses remains to be seen. The US Fish and Wildlife Service has said there's enough evidence to consider the Pacific walrus threatened. A decision on whether the walruses deserve Endangered Species Act protections is expected by 2017.

Right now, the Pacific walrus population is currently at around 200,000 and by some accounts is double what it was in the 1950s, after recovering from decades of hunting. So the main worry isn't about the present — it's about whether walruses will be able to adapt if the ice keeps melting.

Further viewing: Here's a video from the US Geological Survey of an earlier large walrus haul-out near Pt. Lay in 2011:

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