There is no one factor that stands out head and shoulders above the rest. The same factors exist. As Lynda mentioned earlier, we certainly don't blame the decline on harvesting, but what often happens is that as the herd declines, hunters are able to get at the herd with modern technology.
We also see that we're not alone in this. If you look at the circumpolar world, there are a number of herds that are in the same difficult situation, perhaps not as acutely as we see in the Bathurst herd, but this happening everywhere in North America.