A boatload of tourists in the far eastern Russian Arctic thought they were seeing clumps of ice on the shore, before the jaw-dropping realisation that some 200 polar bears were roaming the mountain slope.
"It was a completely unique situation," said Alexander Gruzdev, director of the Wrangel Island nature reserve, where the encounter happened in September. "We were all gobsmacked, to be honest."
The bears had come to feast on the carcass of a bowhead whale that washed ashore, later resting around the food source. The crowd included many families, including two mothers trailed by a rare four cubs each, Gruzdev told AFP.
Climate change means that sea ice, where polar bears are most at home, is melting earlier in the year, so the bears have to spend longer on land, scientists say.
This might wow tourists, but it means that the bears, crammed together on coasts and islands, face greater competition for the limited food resources on land.
Locals are also at risk from hungry animals venturing into villages.
'Changing ice conditions'
Wrangel Island, off the coast of Russia's Chukotka in the northeast, is where polar bears rest after ice melts in early August. They remain there until November, when they can again leave land to hunt for seals.
It is also considered the birthing centre for the species, with the highest density of maternity dens in the entire Arctic, Gruzdev said.
"A whale is a real gift for them," he said. "An adult whale [weighs] several tens of tons" –– so many bears can feed on it for several months.
Studies have shown that, compared to 20 years ago, polar bears now spend on average a month longer on Wrangel Island, because "ice is melting earlier and the ice-free period is longer", said the University of Washington's Eric Regehr, the lead U.S. scientist on the U.S.-Russian collaborative study of Wrangel Island's polar bears.
Changing ice conditions could also be responsible for the increasing number of bears flocking there, Regehr said.
This autumn, the number of bears observed was 589, far exceeding previous estimates of 200-300, he said, calling it "anomalously high".
The International Union for Conservation of Nature estimates there are about 26,000 polar bears in the Arctic, with long-term "potential for large reductions" due to ice loss.
Ice is key, as polar bears hunt exclusively on the surface, often staking out seals by their breathing holes.
Nothing can replace seals
Regehr said the polar bear population in the shared U.S.-Russian Chukchi Sea "appears to be productive and healthy" at the moment, but as time spent on land continues to increase, the bears' nutrition and body condition will be affected.
"The question is at what point the population will begin to experience negative effects –– is that at one-and-a half-months [more time on land than usual], two months... more?" he asked.
"We don't know exactly, but there is a threshold somewhere in the future."
Despite some food sources on land –– including musk oxen, lemmings, or even grass –– nothing can completely replace the energy-packed seals that bears have evolved to rely on.
"They are resourceful and adaptable animals, and some bears will probably find something to eat, but the number of bears we currently have in the Arctic definitely cannot be sustained on land," Regehr said.
That made the image of hundreds of bears around the whale carcass both impressive and concerning, he said.
"There is evidence that it foreshadows the future: larger numbers spending more time on the island and ultimately less time on the sea ice with fewer prey, with a negative cascade of effects."
One effect is the increasing chance of conflict between polar bears and humans –– for example, in native Chukchi settlements, all of which are located on the coast.
Since mid-October, polar bears have been coming dangerously close to a Chukotka village called Ryrkaipy, which is located near Kozhevnikov Cape, an important site for walrus gatherings, called haulouts, that lies about 200km south of Wrangel Island.
With changing ice conditions, walruses may be forced to come ashore in steep, unsuitable areas.
This year, hundreds died as the huge animals crushed one another, possibly after being disturbed by a predator, said Viktor Nikiforov, a polar bear specialist and coordinator at Marine Mammals Research and Expedition Centre.
The problem is that some walrus corpses then floated to the village, attracting polar bears. "One bear broke the window of a house," Nikiforov said.
The village went on high alert, forbade children to walk to school and cancelled some public events, reports said.
Nikiforov said scientists and locals used bulldozers to move walrus corpses away from the village. He echoed concerns that bears spend more time ashore as the ice-free period becomes longer.
"The concentration of people and animals in one area increases and there is conflict," he said.
"We cannot stop climate change, but we can sort out the situation on the shore and make life easier for the bears," he said, referring to measures such as bear patrols to minimise conflict with humans.
"With changes in nature, that has to be attended to."