Like other mammal populations, they produce the largest annual surplus that can be harvested on a sustained basis when they're reduced to something around half of the level they achieve when they're not harvested. If we calculate that, it means if the seal population was reduced by about 50% and then kept near that level, it would produce the largest annual surplus. The pup survival rate would improve considerably.
As the seal population built up on the B.C. coast, the survival rate of pups through their first year of life dropped from about 80% down to around 30%. Starving seal pups wash up on shore and so on, so it's not what you would call a healthy situation from that standpoint for the seal population to be as large as it is.