The media is up in arms today over the imminent starvation of polar bears because they may have to rely on land-based foods for sustenance. But according to Susan Crockford, a zoologist and polar bear expert, the media has missed the point entirely of this new study. She writes that “whatever food polar bears consume in the summer ‚Äì whether they are on land or on the ice ‚Äì doesn’t really matter.” What actually matters is what polar bears eat and how much during the spring.
The most important food that polar bears consume yearly is fat-rich baby seals between March and June. By gorging on these plump little delicacies from late winter to the end of spring, polar bears put on enough fat to carry them “over the summer, no matter where they spend it.” According to Crockford, the authors of this new paper (Rode et al.) have tried to frame the issue as one “about the future survival of polar bears in the face of declining sea ice.” Without enough foodstuff in the surrounding water, polar bears will have to “eat things like berries and bird eggs and even mammals like caribou.” This is because declining sea ice, they predict, will cause the loss of their primary food source, forcing polar bears to live off the land.
Crockford, however, notes that “the fact that polar bears in the Chukchi Sea and Southern Davis Strait are thriving despite dramatic declines in summer sea ice (aka an extended open-water season), proves my point and disproves their premise. Bears in these regions are doing extremely well ‚Äì contrary to all predictions ‚Äì because they have had abundant baby seals to eat during the spring (see here and here).” She makes it clear that the sea ice models used by these biologists “do not predict a decline in winter sea ice (Dec-March),” but rather summer sea ice:
“…all GCMs project extensive winter sea ice through the end of the 21st century in most ecoregions (Durner et al. 2009).” (Amstrup et al. 2007:9)
Indeed, according to their own computer models, the state of the critical spring-feeding period from now until 2050 shows no decline in spring sea ice. Crockford writes that “when you hear or read stories about polar bears and predicted sea ice declines: “sea ice” does not mean spring sea ice.” When asked by InsideScience for a comment on this new study, Crockford told them:
“I agree wholeheartedly with the authors that there is little evidence to suggest that terrestrial foods are important to polar bears now, or would be in the future. However, this squabbling over what polar bears eat, or don’t eat, in the summer hardly matters, since the critical feeding period for polar bears is March to June.
“Chukchi Sea and Southern Davis Strait bears, for example, are doing very well ‚Äì contrary to all predictions ‚Äì despite marked declines in summer sea ice because they have ample food during their critical spring feeding period when sea ice is abundant.”
Crockford makes clear that all this background noise about polar bears eating land-based foods due to decreasing summer sea ice is nothing more than a red herring: “It doesn’t matter what, if anything, polar bears eat in summer — what matters is how much they eat in the spring.“