So, I've been spending a lot of my spare time looking at sea ice dynamics in the North Atlantic in relation to the North Atlantic Oscillation. Ideally, this research aims to make sense of what is - and might - happen to harp seals, and other pagophilic pinnipeds, if global warming greatly effects their breeding habitats. Much of the work involves building an understanding of how decadal-scale climate variability effects sea ice availability for these animals during the breeding season. Once we've teased that out, we can start to study how longer-term or unidirectional climate change may effect these animals.

While looking at the NAO it became clear that the largely positive period during the 1980s and early 1990s was preceded by a negative stretch from the mid-1940s till the mid-70s. The most consistent portion of this negative period occurs during the late 50s and sixties. A graph illustrating the NAO and these two contrasting periods of time is below. The curve in red is a simple spline that accounts for at least 20% of the variation in the NAO data - not perfect but it gets the point across.

Considering that sea ice concentration in eastern Canada is "in phase" with the NAO (see below), it stands to reason that this period exhibited poor ice conditions (we know that 1969 is one of the worst on record), and therefore increased seal mortality. Interestingly, the harp seal population plummeted during this negative NAO period, dropping by at least 55% during 1950 to 1970. During this time seal catches were relatively high…and it seems that the combined effects of reduced sea ice and large harvests may best explain the dramatic drop in seal numbers.

 Ari, Dave Lavigne and I are working on a note about this right now.