The ice charts Derocher uses appears to show only ice that is more than 50% concentration. Compare the ice on his tweet from today (17 July) — which shows barely any ice at all and might be interpreted as showing polar bears in open water.
However, satellites have trouble recognizing some ice at this time of year because of melt water that forms on top of ice (which the satellite may interpret as open water), so there may actually be more ice than is shown even on the CIS charts.
The bears will come ashore eventually, of course — probably within the next week or so, depending on how the melt proceeds. Some are already ashore and others may stay out longer.
Keep in mind, however, that the latest research (Castro de la Guardia 2017 – see abstract below) shows that Western Hudson Bay polar bears in recent years (to 2015) spent only about 3 weeks longer onshore (i.e. 21 days) than they did in the 1980s. Bears left the ice about 2 weeks earlier and left shore about 1 week later — but this hasn’t changed since 2003 (Regehr et al. 2007).
Which means that there has been no change, on average, in the amount of time that most WHB polar bears spent on shore since 2003 and thus, the ice-free season in recent years has not been any worse for the bears than it was 14 years ago.
This entry was posted in Life History, Sea ice habitat and tagged breakup, Churchill, concentration, ice-free season, onshore, polar bear, sea ice, stage of development, western hudson bay. Bookmark the permalink.