A recent study by Norwegian biologist Karen Lone and colleagues, who tagged 57 polar bear females with sensors around Svalbard, discovered that polar bears can dive to a maximum depth of 13.9m and can swim long distances across open water without rest. Contrary to previous claims, polar bears are excellent divers and their breath-holding ability did not seem to limit how deep they could dive.
From the abstract of the new paper by Lone and colleagues (Lone et al. 2018):
“Some bears undertook notable long-distance-swims. Dive depths up to 13.9 m were recorded, with dives ≥5 m being common. The considerable swimming and diving capacities of polar bears might provide them with tools to exploit aquatic environments previously not utilized.”
Compare the above statement to one made by Stirling and van Meurs (2015), after describing a 3 minute dive video-taped during an aquatic stalk of a bearded seal, also in the Svalbard area:
“…increased diving ability cannot evolve rapidly enough to compensate for the increasing difficulty of hunting seals because of the rapidly declining availability of sea ice during the open-water period resulting from climate warming.” [my bold]
These two papers really show the difference between using anecdotal accounts as if they were evidence of species-wide physical abilities and doing a scientific study on the physical ability of interest.