Seems the polar bears found a food source even though the ice floes are decreasing. The source was walruses. But walruses were already a source. It seems the walrus, who nested and raised young on floes had to go ashore where the polar bears were stranded.
The walrus actually likes the shore. In fact large herds are frequently found on the Russian shore of the Chukchi Sea. With the ice retreat, the Alaska shoreline became available to the herds. The shore habitat is the equivalent of a mall food court. The ice floe habitat is like a mom and pop grocery in rural area. Where would you choose to live?
The benthic organisms walruses prefer are not produced on an ice covered shore. Once the shore is exposed they flourish. They still exist on the shallow sea floor. In the fact the sea floor is the source for the exploding onshore feast.
Being onshore makes the walrus more susceptible to predators such as the polar bear. Whoops, circular logic here. The walrus was the prey of the polar bear on the ice floes. Now they are the prey of the bear on shore. What is the difference?
Environmental niches begin at the bottom of the food chain, starting with plankton. As that supply expands or contracts the animals above on the chain follow the food source. When the source diminishes all the animals up the chain diminish.
A predator like a polar bear will seek alternate food sources. Caribou herds would be a choice. Bears usually avoid caribou because the chase to run down one is exhausting. Increased attacks on man-made settlements are the true indicator of habitat deficiency. There have been no reports.
Perhaps the walrus and bear are no different than man. When it heats up, just go to the beach and enjoy life.
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