Tuesday, June 11, 2013

Polar Bears Bask in Global Warming

Exciting news about polar bears in eastern Canada: the peer-reviewed paper on the Davis Strait subpopulation study has finally been published (Peacock et al. 2013). It concludes that despite sea ice having declined since the 1970s, polar bear numbers in Davis Strait have not only increased to a greater density (bears per 1,000 km2) than other seasonal-ice subpopulations (like Western Hudson Bay), but it may now have reached its ‘carrying capacity.’

This is great news. But where is the shouting from the roof-tops? This peer-reviewed paper (with its juicy details of method and analysis results), considered by some to be the only legitimate format for communicating science, was published February 19, 2013. No press release was issued that I could find and consequently, there was no news coverage. Funny, that.
"Eskimos are tasty, but Climatologists are easier."

There was a bit of shouting back in 2007 when the study ended and the preliminary population count was released – polar bear biologist Mitch Taylor is quoted in the Telegraph (March 9 2007) as saying:

“There aren’t just a few more bears. There are a hell of a lot more bears.”

"I guess I should have turned right at Albuquerque"

There was also a CBC news item in January 2007 and a Nunatsiaq|Online report in October 2009 when the official government report was completed. But these were all based on preliminary information and focused on the population increase only.

This new paper (Peacock et al. 2013) reveals that the story in Davis Strait is about more than simple population growth. Small wonder no one is drawing attention to it.
"Hey, I'm tied up, but you can walk to Florida"

Davis Strait is most southerly subpopulation of polar bears, because some bears move down as far as southern Newfoundland (470N) when sea ice is at its maximum in the spring. Davis Strait, in total area, is almost as large as the three Hudson Bay subpopulations together – Western Hudson Bay, Southern Hudson Bay and Foxe Basin – according to area data given by Vongraven and Peacock (2011). However, a lot of that area is land and not all of the water is ice-covered, even in late spring. The actual “suitable ice habitat in spring” (determined by Taylor and Lee 1995) averages only 420,100 km2, which is about 16% of the total area.
"Tourists aren't as tasty as climatologist, but they're more common"

The new study, by Lily Peacock, Mitch Taylor and two other colleagues, compared data from mark-recapture studies done in 1974-1979 to those undertaken in 2005- 2007. They state that in Davis Strait, “the overall amount of sea ice declined and breakup has become progressively earlier” since the 1970s.

However, in spite of this decline in sea ice, they estimated the number of bears at about 2,158, a substantial increase over the estimate of about 1,400 bears in 1993 (Derocher et al. 1998:27 – see previous discussion here).

Peacock et al. note that the density of bears in Davis Strait comes out to 5.1 bears/1,000 km2 of sea ice habitat, which is “greater than polar bear densities in other seasonal-ice subpopulations, which are approximately 3.5 bears/1,000 km2 (Taylor and Lee 1995).” Bears in Hudson Bay, for example, also live in a ‘seasonal-ice’ habitat.
"It's getting pretty crowded around here"

Peacock et al. characterize the Davis Strait subpopulation as having “low recruitment rates [low birth rates], average adult survival rates, and high population density” and conclude – here’s the kicker – that “low reproductive rates may reflect negative effects of greater densities or worsening ice conditions.” [my bold]

In other words, this subpopulation is showing changes expected in populations affected by declines in sea ice or one that has reached its carry capacity (i.e. “negative effects of greater densities”) but that it is not possible to distinguish between the two.
"Just as soon as you're out of the den, I'm swimming to Bermuda"

This is actually not the first time this conclusion has been reached. As discussed previously here, Andrew Derocher (2005) stated in regards to his study of Svalbard area polar bears in the Barents Sea (1988-2002): “given that the population may be showing density-dependent responses, it is not possible to differentiate the climatic effects from population effects.”

Found at Watts Up With That.

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