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.
Posted in Advocacy, Life History, Sea ice habitat
Tagged continuous swims, depth, dive, harbour seals, polar bear, Spitsbergen, stalk, Stirling, Svalbard, swimming, underwater
Contrary to what the misleading press release implies, an entirely speculative new paper by polar bear specialists Kristin Laidre and Ian Stirling (among others) presents zero evidence that polar bear consumed whale carcasses during the last warm Interglacial (Eemian, ca. 115-130kya). And contrary to the impression that Eemian conditions were very challenging for polar bears, simulations from the single paleo sea ice simulation paper these authors cite show the ice-free season over most of the Eemian was less severe than today in the polar basin, with no reason for polar bears to scavenge extensively on large whale carcasses.
Polar bears are shown scavenging on the carcass of a dead bowhead whale that washed ashore on Wrangel Island, Russia. Credit: Chris Collins/Heritage Expeditions
This is yet another paper posing as science co-authored by Stirling that uses anecdotal accounts of behaviour to send a message about evolutionary capabilities of polar bears (Stirling and van Meurs 2015). With little or nothing to back it up, the paper’s real purpose is to convey Stirling’s opinion that past polar bear survival is irrelevant to understanding future polar bear survival — and that all the bears are gonna die unless we do something about carbon dioxide emissions generated by fossil fuel use.
Is it a coincidence that the Summary for Policy Makers was issued by the IPCC over the weekend (not the report with the science in it but the document that all politicians agreed were acceptable)? Look no further than the last sentence of National Geographic’s article on this story, which includes a quote from lead author Laidre and a link to the magazine’s interpretation of the new IPCC report:
“Laidre put it even more bluntly: “If you want polar bears around we need sea ice, and loss of sea ice closely tied to our activities and our fossil fuel emissions.” (Learn about the IPCC’s dire new climate report.)”
Posted in Advocacy, History, Life History, Sea ice habitat
Tagged anecdotal observations, carcasses, dead whales, Eemian, interglacial, models, polar bear, sea ice, whales