When the shorefast ice gets too thick seals move away because they can’t maintain their breathing holes. Polar bear populations have suffered in the past in the coldest winters. The main starvation time for polar bears is in March – after they have been on the ice all winter!
– While polar bears that spend extensive time on land during the summer months (such as those in WHB) may fast for up to four months, previous research has shown (Stirling and Øritsland 1995) that bears in most regions are at their lowest body weight in spring (i.e. March). This suggests that winter fasting leading to starvation may be a more limiting factor for polar bears and this may be particularly true if winters are associated with development of especially thick shorefast ice. Such cold winters in the past, as occurred during the mid-1960s, mid-1970s, mid-1980s, and early 1990s, led to marked reductions in polar bear numbers (Stirling 2002; Stirling and Lunn 1997) due to dramatic declines in availability of young ringed seals. In Greenland, ringed seals are known to move offshore when shorefast ice becomes too thick for them to maintain their breathing holes (Vibe 1967).
Some bears live their entire lives on sea ice. Polar bears survive very well on "first year" ice. This is a sample of the polar bear information that can be found at this site.