Cederholm, et al.:

Recent calculations by Gresh et al. indicate that only three percent of the marine-derived biomass once delivered by anadromous salmon to the rivers of Puget Sound, the Washington Coast, Columbia River, and the Oregon Coast is currently reaching those streams.
Pacific Salmon and Wildlife, 2000, p iv

how does this compare to other periods when the oceanic conditions were not conducive to large runs of spawning salmon? not just to the recent past.

Recent calculations by Gresh et al. indicate that only three percent of the marine-derived biomass once delivered by anadromous salmon to the rivers of Puget Sound, the Washington Coast, Columbia River, and the Oregon Coast is currently reaching those streams.