Here is a recent citation where they estimated the amount of chinook salmon taken by pinnepeds, orcas, and fishing from 1975-2015.
https://www.nature.com/articles/s41598-017-14984-8They conclude that whales currently account for approx twice the biomass of chinook as seals, and total consumption by marine mammals has risen from ~6K to 15K over that time period. Depletion due to fishing harvest decreased over that time from ~16K to 10K tons, not quite enough to offset the increase from marine mammal predation. They speculate that this increase in competition from other marine mammals in recent years may now be a greater factor for the SRKWs than fishing harvest.
There's a lot in that paper, so correct me if I'm interpreting it inaccurately.
they take 20x more of a much less signficant portion of the salmon biomass. As is important they have no historical data on what seals may have taken in the past (perhaps the % they take is historically normal) and little real idea if the high seal consumption is mostly a result of hatchery enhancement of chinook and other salmonid stocks.
2% or less of outgoing smolts survive to return as adults.
Obviously total mortality rate is impacted by many sources, but the paper estimated that the vast majority of smolt predation by the marine mammals studied came from harbour seals which accounted for 6.5% of total smolt production. Still a small proportion of total mortality, but increased from 1.5% of total smolt production in 1975. Not to suggest that magically eliminating seal predation would result in proportional increase in survival, but certainly must be some factor.
The paper does note that increase of predation may be in part due to hatchery enhancement and that increase in hatchery production could have subsidized pinniped population increases.
A complex issue to be sure.