Human impact is infinitely greater than seal activity. From the perspective of most forms of wildlife, and "natural" balance within and between ecosystems, humans are a virulent disease. A truly pristine ecosystem, anywhere on the globe, is an historical nicety.
Rod states that S of G seal population is thought to be similar to 1800's number; it seems that their food sources have not enjoyed the same rebound.
One of the main pillars of wildlife management is that once a "balance" has been upset, it is our responsibility to help restore that balance. One of the most logical and efficient tools to do so is a seal cull, since a human cull is unpopular.
Sadly, this will never happen for two primary reasons: 1) there are too many whiny (misdirected) animal lovers among the public, who see seals as cute, little, huggable playthings, often in pretty white coats (harp seal pups). 2) DFO "manages" such things and couldn't manage a dogfight.
tc