The difference is a very large number of species prey on salmon at their varying life stages and exactly zero species prey on seals. Some killer whales obviously eat seals, but the pods that do so are rarely, if ever, in Puget Sound or the southern Strait of Georgia that they have no measurable impact on the harbor seal population.

Seal population growth is regulated only by the abundance of their prey. This said, once people stopped smoking seals indiscriminately out of fear of federal court, there was nothing stopping seal population growth. After talking to old timer anglers, commercial fishermen and Indians, I came to realize just how many seals got shot on a regular basis decades ago. This simply doesn't happen anymore, at least not at a rate that impacts growth.

In regards to not killing 50% of fish before they can spawn: we no longer kill any more than a negligible number (and in some cases zero) of wild steelhead yet steelhead populations in Puget Sound are not experiencing growth or are still declining. If the abundance of spawners does not influence overall population size, then there are other factors limiting population abundance and this could be true for coho and chinook. This is similar to putting $4,500 into your savings account with a 0.05% interest rate and getting disappointed that it's not making you any money.

Every year more information comes out just how massive the impacts seals are having on salmon and steelhead. These impacts are not just on returning adults, but are also on juvenile chinook, coho and steelhead at astounding numbers.

I'd wager within 10 years, there will be public debates on the "ethical" number of seals to be culled.