The watershed is the metric. For salmon, particularly coho, they spawn high, as far as they can go, and rear low. They need food in the lowlands.

But, we have to consider the needs of all the species and how they interact.

Chinook are Big Water fish. They matured at 30-50 or more pounds and needed big water to spawn in. Mainstems. Plus, they spawn in August/September when the rain driven streams, like Willapa, are at their lowest and warmest. That's why WB is not Chinook land. They want lots of water.

Chum typically spawn low in the watershed, but almost everywhere. They do go way upstream, too. Used to be chum in the Walla Walla. I think there are, or were, Yukon chum in Canada, eh. They are the primary deliverers of nutrients because they basically just import them, They don't rear much in FW, so their carcasss are for everybody else.

Coho, as I said, spawn high and rear low. We used to think that they only produced yearling smolts so they needed to overwinter and thereby were overwinter habitat limited. Nope. They can smolts as fry, as fingerlings, as Fall migrants, and as yearlings. The more fry in the creek, the more outmigrants of the other types. Used to think they were stream fish. They dearly love lakes and lakes are so much more productive of smolts, and bigger smolts (higher marine survival) than streams. Their carcasses are most desired by juvenile steelhead.

Pinks, like chum, are givers rather than takers. Plus, they spawn in the same places and time as Chinook. Cleaning the gravel for Chinook and setting the table for the next spring's fry.

Sockeye, in most situations, feed themselves.