Polar Bear Status: In Decline

Monday, May 23, 2011 - 09:26

Dr. Steven C. AmstrupAs a member of the IUCN Polar Bear Specialist Group (PBSG), and a scientist who has studied polar bears for more than 30 years, I feel compelled to point out that —intentional or not—it’s wrong and misleading to suggest that the most recent report from the PBSG concludes that there’s been “no change” in overall global polar bear population status.

A recent article titled "No Decline in Polar Bears Populations," written by CNSNews and picked up other sources, correctly states that our group concluded that one of 19 polar bear subpopulations is currently increasing, three are stable, and eight are declining mainly due to global warming induced loss of critical sea ice habitats. It failed, however, to note that this compares negatively with our last report in 2005, which found that five subpopulations were declining, five were stable, and two were increasing.

Lone polar bear In the proceedings of our 2001 meeting, we reported only one population known to be declining and suspected one other might be. So, over the last decade, the global trend in polar bear populations has been solidly negative: In 2001, we reported only one population in decline. By 2010, the number of declining populations had jumped to eight.

In 2010 as in 2005, we had insufficient data from seven populations on which to base a decision to know what their trend might be. However, sea ice trends in the regions occupied by these data-deficient subpopulations suggest population sizes in many of them also probably are now declining.

The “20,000 to 25,000” estimate for the number of polar bears worldwide is only a rough guide regarding what the global population might be. It is a combination of good measurements in some populations, poorer quality information from other populations, and little or no information from the seven subpopulations where we could not assess a trend. The possible range in the global number, therefore, is wide and our information is insufficient to say what the global number is now or what it was a few years ago.

The important information in our report is that where we do have quantitative information, we have seen declines in physical stature and condition, declines in reproduction and survival, and declining population size due to sea ice losses induced by global warming. The world can only warm as greenhouse gas concentrations continue to increase and a warmer world will hold less sea ice habitat for polar bears. Polar bears are highly adapted to foraging on the sea ice and it is only from the surface of the ice that they are consistently able to catch their preferred prey. There is no evidence they can persist on terrestrial foods that may be available in a dramatically reduced sea ice environment.

Ultimately, if we allow the warming to continue, habitat loss will negatively affect all polar bears. For that reason, the most recent PBSG report restates the conclusion from our previous report-that global warming is the single most important threat to the future welfare of polar bears worldwide. At their recent meeting in Tromso, Norway (2009), the parties that signed the International Agreement for the Conservation of Polar Bears, also recognized that global warming induced sea ice decline is the greatest threat faced by polar bears.

Dr. Steven C. Amstrup, Chief Scientist, Polar Bears International

Photos by Daniel J. Cox/Natural Exposures.

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