Scientists monitoring the animals say that there is a decline in the birth rates and the general well-being of the bears.
The only noticeable improvement tallied exactly with an exceptionally cold year following the eruption in 1992 of Mt Pinatubo in the Philippines, throwing ash and gas into the atmosphere.
Nick Lunn of the Canadian Wildlife Service told New Scientist magazine that there had been a long-term decline in the condition and reproduction of female bears.
Recently the floes have begun to melt earlier as a result of regional warming in the Arctic, threatening the bears' survival.
In April the Hudson Bay bears wait at ice holes to catch young seals, which come to the surface to breathe. Pregnant females gorge themselves with food before the ice melts. They then spend eight months, from July to March, in hibernation.
In that time they give birth and lose up to half their body weight, which must be regained on the ice if they and their cubs are to survive.Reuse content