Just had the chance to read a couple of the latest research papers about polar bears – both are pretty interesting and open a bit of an eye into the changing world of polar bears.
The Southern Beaufort paper (Polar Bear Population Dynamics in Southern Beaufort, Bromaghin et al, 2014) is circulating through the media as a ‘bad news’ story for bears, with the population declining by up to 50% from 2004-06. This has unfortunately overshadowed the fact that the population itself rebounded after 2006 and was only slightly reduced by 2010. In fact, when you read the paper, it actually provides a number of signs for hope for polar bears.
The most interesting part of this paper involves a record low sea ice year. 2007 was essentially the ‘perfect storm’ for sea ice decline. The multi-year ice in the Beaufort Sea had fractured and was showing signs of movement. At the same time, an arctic ‘cyclone’ hit the area and sped up this process of breakup. The ice sheet dispersed and resulted in an historic low in sea ice cover for the Arctic (at least, since 1979…).
Surprisingly, the Southern Beaufort population actually began to recover after this event. In years of heavier ice (2004-06), the population experienced a fairly significant decrease yet in very ‘poor’ ice years in the west, it began to recover and stabilize. In the study itself, it is suggested that sea ice cover is not the only factor that contributes to polar bear survival in these areas and also cites a reported increase in seal kills in unstable ice and essentially open water.
The Southern Beaufort bears appear to be returning to land as well. Hunting pressures and development caused this population to den on the ice and travel with the pack. A change in hunting levels as well as the bowhead harvest along the coast near Barrow and Kaktovik are now resulting in more terrestrial foraging and even denning, this is actually a positive change since early landfast ice actually provides a better seal hunting platform than bear find out on the pack ice.
The other paper investigates changes in the on-ice range of the Western Hudson Bay polar bears. This paper has discovered that ‘Churchill’s bears’ may now be ranging further out onto Hudson Bay, around 200km off shore, and further north and east. Instead of ending at the Ontario border, females from this area travel much further south. This does not come as a total surprise given than ice patterns and wind patterns have changed along western Hudson Bay. However, in this paper, there are a couple things that seem to up-end some of our longheld beliefs about Hudson Bay’s polar bears.
Females were long believed to return to their denning area in Wapusk National Park as the sea ice melted and progressed further south, coming ashore around two weeks earlier than the rest of the population. There now seems to be some indication that females are staying out on the ice longer, possibly riding it to the bitter end and maybe ending up further south than traditionally believed. Pretty interesting.
The summary of Hudson Bay’s seal population is also of interest. It is often forgotten that seal pupping in Hudson Bay has actually increased considerably since the 1990s. To me, this was probably the most significant factor to the population decline between 1988 and 2004. After a significant volcanic eruption, late summer ice resulted in very favourable conditions and survival of polar bear cubs – dubbed the Pinatubo bears. However, this high survival rate of cubs would have also come at a time when seal birthing rates were dropping in Hudson Bay. This likely would have meant that ‘fringe’ participants in the population would not have survived and that the Pinatubo bears may have dominated the food source. More bears competing for less seals… tricky.
By the early 2000s, a period of poor sea ice conditions, seal pupping rates tripled but the bears’ access to these seals would have been reduced in the spring from early sea ice breakup. This increase in production does seem to correlate with an increase in open water seal kills witnessed in Churchill’s bear tourism season (2004 to present). At first, we thought that maybe seals were washing ashore from some disease or event but now it just seems like there were a hell of a lot of seals in Hudson Bay. Cool.
And finally, the paper seems to show that our traditional belief that polar bears ranged around a series of leads and cracks in the ice near the low tide area was either mistaken or has changed. The main feeding area seems to be well off shore, 100-250 kilometres offshore, generally to the northeast of Cape Churchill.
So, that’s pretty cool – things are changing for polar bears but polar bears seem to be coping and adapting at least on some level. And that’s good news.