You mean they don't migrate south in the summer? How can they survive the rising extreme heat of Arctic summers? Does Al Gore know about this?
Are you SURE they don't float down there on icebergs, (and float back again 6 months later) and the reason they're going extinct is that the hotter oceans now melt the bergs too soon, and they drown?
Source: http://tennesseeaquarium.blogspot.com/2007_05_01_archive.html