One of the the factors that depresses freshwater production is lack of nutrients. The steelhead are doing poorly for a lot of reasons, but lack of food in the river is a biggie. Data from WA and BC both show that the younger the smolts, the higher the R/S. The primary source of nutrients in the N Pacific freshwater systems was nutrients delivered by spawning anadromous fish; the salmon, lampreys, smelt. Base level productivity is low.

This was shown rather clearly in AK with the pink and coho. The kicker is that abundant adult coho outcompete the salmon in the ocean.

When BC first showed that nutrient levels were controlling steelhead abundance they warned folks that simple nutrients weren't the silver bullet that would save the fish. It is a piece, but only that.

The fish need water, clean and cold. They need stable streambanks with a good mix of habitat, they need functioning estuaries with reasonable levels of predation, they need marine waters without plastic (apparently oceanic steelhead eat a lot of it) and toxics, they need a prey base in the marine waters to allow them to grow, they need less exploitation so that they can grow to adulthood and return, for steelhead we need repeat spawners.

This is, in my mind, one of those thousand piece puzzles and most folks don't want "their" piece used. They want the other 999 to be used to fix it. Meanwhile, humans continue to reproduce.