Thursday, September 3, 2015
Are Polar Bear Populations Thriving?
I wish polar bears were thriving; unfortunately, they're not.
Complicated issues are difficult -- if not impossible -- to convey in a meme. It make take a bit of time and effort, but for those interested in facts here you go:
When Al Gore was born in 1948 there were no legitimate estimates of how many polar bears existed – guesses varied widely because they were based on stories from explorers and hunters rather than scientific surveys. Before the polar bear treaty was signed in 1973, and before polar bears were listed as endangered, several populations of bears were decimated by hunting which began around 1600 and continued unchecked for 350 years. Early scientific estimates from the 1980s, after polar bears were protected for a decade or so, are in the neighborhood of 20,000 to 40,000 polar bears. Most researchers assume that the number of polar bears did increase due to the controls and quotas instituted by the 1973 treaty.
Today, researchers estimate that there are 20,000 to 25,000 polar bears in 19 relatively distinct sub-populations. Of those 19 sub-populations, eight are declining; three are stable; one is increasing and, for the remaining seven, there is insufficient data to determine. For comparison: In 2005, five populations were declining; two were stable and two were increasing. (There is insufficient data for the others.)
Currently, most of the populations are losing sea ice habitat which has negative impacts on their hunting, as a result most populations are experiencing declines in weight and health of bears, along with low reproductive and cub survival rates.
Since satellite records began in the late 1970s, about 50% of the ice area has within polar bear habitat has been lost, and the ice that remains has lost about 50% of its thickness. In 2012, the area of sea ice loss was greater than the entire area of the United States. That is a significant degradation of critical habitat for polar bears.
Because polar bears feed almost exclusively on seals they hunt on ice. Changes in the sea ice that affect access to prey has and will continue to have negative effects on the bears. In particular, if more snow falls, polar bears are less successful at breaking into the birth lairs of ringed seals. If too little snow falls, ringed seal pups are born on the sea ice without a lair and this makes them very vulnerable to predation by polar bears and arctic fox -- which can lead to a decline in seals. With less food, polar bears will fail to reproduce more often and give birth to smaller young that have higher mortality rates.
Unfortunately, polar bears are not "thriving" and their future doesn't look so bright.