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Polar Bear Blog – The Roaring Nineties

The 1990s were a turbulent time for Churchill’s polar bears, it is really through this decade that we get a glimpse as to how drastically changing sea ice and weather patterns can affect bear populations.

The 1980s are often seen as peak bear years in Churchill.  Ice conditions were favourable, especially in the late 1980s and there was some thought that the population was reaching carrying capacity by the end of that decade – that is, the seal population could not support any more bears in the area.

Then, in 1990, disaster struck.  In March of that year, it rained.  Spring rain is almost unheard of along Hudson Bay, it really is still mid-winter – summer doesn’t show up until early July…  As a result, several maternity dens caved in suffocating the females and cubs inside.  Population studies that year recorded a quite significant drop.

As well, this rain event likely opened up seal birthing lairs on the ice so that the bears that were out there had a pretty productive year.  The downside of this is that seals may have been over-harvested that spring… its hard to say.

Then in 1991, Mount Pinatubo erupted in the Phillipines.  The resulting ash cooled the atmosphere and the 1992 ice season in Hudson Bay was significantly extended.  Cubs that were born that year got a real ‘headstart’ on life.  They would later be known as ‘Pinatubo Bears’, growing to be large, healthy animals – seemingly bigger than bears born in average ice years.

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The tricky part is that heavy ice was not necessarily good for seals and the combination of the rain event one year, then heavy ice and a longer hunting season two years later, meant that seals were fairly scarce in the early 1990s.  The population did not recover for another ten years.

So, the western Hudson Bay bears were under a bit of pressure in the 1990s, lower seal population plus a cohort of bears that could outcompete bears born in mid-decade.  Seal hunting season was shorter than the 1980s but conditions were still okay.  Then, the decade finished as it had started, an epic disaster for the western Hudson Bay bears.

In both 1998 and 1999, the bay was pretty much open by the first week of July and the bears were onshore in June, over a month early.  Spring is a critical seal hunting season and early breakup of even just one week let alone a whole month can be fatal for some bears, especially the very young and very old.  Two consecutive seasons of disaster pushed this population over the edge and after twenty years of relatively stability, this population dropped by almost one quarter over a relatively short period of time.

As nature is wont to do, things kind of balanced themselves out.  The increased open water season and decreased numbers of bears seems to have given the ringed seal population a chance to rebound.  By the early 2000s, seals were abundant and ice conditions began to stabilize.

 

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