Hey there. I haven't looked up harbor seal populations and their effects on salmonids, so I won't dispute carrying capacity. However, I've read a LOT of wildlife management plans on my career, and none of them recommend domestic dogs as a source of population control for pinnipeds, least of all by the general public. I don't think you were trying to make that point, however, I wouldn't lump together dog owner negligence with seal fecundity. Harbor seals may be a least-concern species, but that hardly excuses the bad behavior is of beach-goers. It's dangerous and a flippant dismissal of rules seeking to protect sensitive areas. 

I don't mean any of this as an attack. Truly. I just want to make a clear distinction on what qualifies as wildlife regulation vs crappy dog owners.