Books with title Polar Bear: Shrinking Ice

It was early September 2009. Researcher BJ Kirschhoffer was in Churchill, Canada, to study polar bears. It didn't take long, however, for him to notice that something was wrong. There were bears all over the place, but many did not look healthy. Some were so skinny that BJ could see their ribs through their white fur. Why weren't these bears getting enough food to eat?