Saw a paper on the Snohomish system that estimated loss of coho smolts due to habitat changes in the lowlands. This included loss of beaver ponds, swamps, and all the other improvements we have added like dikes and levees. Current smolt production is something like one third of what it used to be. And the Snoho produces (or at least recently produced) a lot of wild coho.

Another "loss" is all the lowland lakes that used to connect to anadromous waters. Coho used to rear and overwinter in them. System I worked on produced 10-15K coho smolts in the creek. The lake got cleaned out of spiny rays and now can kick out 30K on its own. Most of those lakes had screens installed on them to keep planted rainbows in. Imaging the coho production possible if those lakes worked as God intended.