Tag Archives: carrying capacity

Mass haulouts of female Pacific walrus as a sign of population health

Posted on October 7, 2014 | Comments Off

Mass haulouts of female Pacific walrus and their calves in fall don’t happen all the time but they do occur. I recently pointed out (here and here) two instances of such incidents from the 1970s.

I said this provided evidence that the September 2014 incident reported in the media was not “a new phenomenon” for this region, as WWF spokepersons and Alaskan biologists have claimed (reiterated in this PBS interview).

Figure 1. Walrus females and calves hauled out on a beach in Svalbard, photo accompanying an October 6, 2014 news report in “Eye on the Arctic” of the rapidly increasing Atlantic walrus population there. (Photo: Thomas Nilsen, Barents Observer).

One aspect of the recent occurrence of a large herd on an Alaskan beach that apparently needs reiterating is that the population of walruses declined rather markedly after a 1970s peak and has rebounded since. This suggests that huge herds of females and calves hauling out on beaches in the fall to feed might only be seen when the population is very large.
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Posted in Life History, Sea ice habitat, walrus

Tagged carrying capacity, Chukchi Sea, climate change, females and calves, global warming, haulouts, mass gatherings, mass mortality, migration, polar bear prey, population size, sea ice declines, stampede, walrus

High walrus numbers may explain why females and calves are hauling out in droves

Posted on October 4, 2014 | Comments Off

Are the recent mass gatherings of females and calves on the beaches of western Alaska and the Russian Far East a sign that population are again close to the limit the habitat can support, as they were in the 1970s?

At the risk of belabouring the point that lack of sea ice does not seem to be a reasonable explanation for this phenomenon (see my last two posts, here and here, and Andrew Montford’s excellent additions here), I think this is a possibility that needs to be considered.

Walruses at Point Lay Sept 27 2014 NOAA CMDA0007_sm

2014 Point Lay, NOAA photo

Walrus are well protected in the US and Russia, and population numbers have risen again since the 1990s, after significant declines in the early 1900s and again in the 1980s.

A paper from the late 1980s suggests that a return to high population numbers may be a more plausible cause for mass gatherings of females and calves that lead to stampede deaths than does reduced sea ice due to global warming.

Have a look and see what you think. It may not be the only reason but it may be a major contributing factor.

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Posted in Advocacy, Sea ice habitat, walrus

Tagged carrying capacity, Chukchi Sea, climate change, females and calves, global warming, haulouts, mass gatherings, mass mortality, polar bear prey, sea ice declines, stampede, walrus

Signs that Davis Strait polar bears are at carrying capacity

Posted on June 10, 2013 | Comments Off

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.

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.”

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. Continue reading

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Posted in Population, Sea ice habitat

Tagged Arctic ice death spiral, carrying capacity, Davis Strait, density-dependent response, Derocher, Peacock, polar bear population density, population increase, population size, sea ice extent, Taylor