The last paragraph is misleading.
They are picking out a specific small population of bears in the Western Hudson Bay, and deliberately glossing that fact over. The overall population of polar bears is in the 21,000 to 25,000 range, with about 15,000 being in Canada. This is much larger than it was in the 70s, with the increase largely due to hunting controls and conservation measures taken back then. Hunting is a much larger issue with the bear population than climate is.
In some areas, the population is increasing, and in most areas, it's stable.