While all the polar bear scientists are chatting about solutions for the apocalypse, I stumbled across a neat little chart of Ice-Free Days in Hudson Bay (page 17). It was used by Martin Obbards, the Southern Hudson Bay polar bear guy, in a presentation so one would assume that the data is reasonably correct.
One thing struck me, the ice in the 1970s kind of looks, um, really average. So with a ruler and some squinting, I tried to chart out the ice-free days from the early 1970s to 2012 (the last five years of estimates are from my blog…). Its really rough but it should give an idea of how things have gone for Churchill’s bears over the years.
Ice Free Days – Hudson Bay 1971-2012 (Bears are actually on land a fair bit longer than this, of course, but it gives an idea of changes in their annual cycles for sure…)
1971 – 80 days
1972 – 80 days
1973 – 110 days
1974 – 110 days
1975 – 110 days
1976 – 100 days
1977 – 110 days
1978 – 80 days
1979 – 110 days
Like I said, the seventies are surprisingly average ice years – likely not great, not bad for bears. Average is about 100 ice free days per year.
1980 – 90 days
1981 – 120 days (early breakup, late freeze)
1982 – 90 days (cub survival rate 60-65%, yearling survival 60%)
1983 – 90 days (population est. 900, some females weaning cubs at 1.5 years)
1984 – 90 days
1985 – 80 days (very late breakup, population est peaks at 1,500)
1986 – 70 days (very late breakup)
1987 – 100 days
1988 – 110 days (cub survival now 50%, CWS Mark-Recapture Study – 1,194 bears
1989 – 90 days
The 1980s are heavy ice years with two record late break-ups, average 90 ice free days. Polar bear population seems to drastically increase (hard to say for sure though) and cub production is the highest in the world.
1990 – 90 days (females now weaning cubs at 2.5 years)
1991 – 110 days (bears ashore July 24, yearling survival rate very low – 15-20%)
1992 – 80 days (very late breakup, three weeks late – bears ashore August 15)
1993 – 100 days (bears ashore July 30, cub survival up to 70% trhu 1997)
1994 – 90 days (bears ashore August 20)
1995 – 90 days (Population estimated at 1,200 bears)
1996 – 110 days (bears ashore August 5)
1997 – 90 days (bears ashore July 24)
1998 – 140 days (very early breakup, very late freezeup)
1999 – 150 days (very early breakup, very late freezeup)
The 1990s actually start well and the population is fairly stable until 1998 and 1999 which are truly catastrophic years for bears. Including 1998/99, its about 105 average ice free days…
2000 – 90 days (very late breakup)
2001 – 140 days (very early breakup)
2002 – 100 days
2003 – 110 days
— CWS mark-recapture results – 935 bears
2004 – 80 days (very late breakup)
2005 – 110 days
2006 – 130 days (early breakup, late freeze)
2007 – 110 days (early breakup)
2008 – 100 days
2009 – 80 days (very late breakup)
2010 – 120 days – late freezeup
2011 – 110 days – early breakup
— GN/MB Aerial Study – population estimated 1,000
2012 – 90 days
The last ten years or so are, to say the least, erratic. There have been absolutely mega ice years with 2004 and 2009, some very bad years 2001, 2006, 2010 and a bunch of average years. About 105 ice free days average…
What is interesting are the years leading up to the two studies that much of the current panic stem from…
1988 – 1,194 bears… this mark-recapture study would have covered that absolute peak of ice conditions for Churchill’s bears including two very late spring break-ups.
2004 – 935 bears… 1998 and 1999 hammered this population, there can be no doubt. Follow that with another poor season in 2001 and I can understand how you could lose 20% of the population – not over 15 years but more like four or five years. I mean that WAS the major ice incident that Derocher and everyone are now saying we must plan for… Nature is tough.
But she is fickle too. 2004 and 2009 were monster ice years… 1992 was a similar late freeze – here is Ian Stirling’s account of the effects of that year…
‘The major divergence from the pattern of declining physical and reproductive parameters occurred following the 1991 eruption of Mount Pinatubo, when cooling over the northern hemisphere (McCormick et al., 1995) delayed the breakup of ice in western Hudson Bay by three weeks or more (Stirling and Derocher, 1993). Apparently because they could feed for three weeks longer, both males and females came ashore in better condition. In the following year, the females’ natality and the survival of their cubs were significantly greater than in previous years (Stirling and Lunn, 1997).’
In normal speak, that basically means a late freeze up is good for bears! I mean I sure have been seeing a lot of subadults running around these past few years… who knows maybe some mothers weaned their cubs at 1.5 years again – wouldn’t that be somethin’!
Either way, things don’t look ‘great’. But, it does not look like we are losing a week of ice per decade as is often reported… plus the late freezes in 2004 and 2009 have to have had a beneficial impact on this population even with longer ice free seasons in between. This leads me to believe that Western Hudson Bay population is either stable or showing slight growth.
1,000 bears is a number that I can buy into… 650? not a chance. 900 possibly… Food for thought anyway. Sure would be nice to see the new Mark-Recapture Study released soon… before we start shipping bears to zoos and building ‘temporary holding’ facilities along the coast for Derocher’s final solution…
Some neat dates from the Ice Chart…
Latest breakups on record – mid-August – 1992, 2004, 2009
Very late breakup – August – 1985, 1986, 1989, 1994, 2000
Early Breakups – mid-July – 1991, 1993, 2005, 2006, 2011
Earliest Breakup – end of June/first week July – 1999, 2001, 1998
Latest Freezeups – 1998, 1999, 1981
