This is off the top of my head, so corrections by more worthy may be in order:
First, salmon will return to their natal river, wild fish or "tame" (hatchery).. I believe the smolts/fry at a certain stage in their life can be introduced to non-hatchery rivers and they will return to that introdutory river, rather than their hatchery. The Kasilof River locally has a king hatchery on it, which produces fishable runs. The hatchery fish have clipped adiposes - you can keep them. Any intact adipose fish is consider "native to the river" and must be released without removing from the water. It's a certainty (to me), that un-caught hatchery fish are now contributing offspring to the "natural, fish, but it is all the same river water.
There are some salmon runs in Alaska (Pebble Mine area) that spawn in Glacial streams with high turbidity. They just do it after the glacer silt goes way down in mid-winter, after the glaciers quit melting. This may not apply to the question, however. Just that fish are adaptable, over time, to varying conditions..
They, like other animals, can also expand home ranges naturally, albeit slowly. Native fishermen wanting to get rich, or go MAGA on their dog and winter food stocks, many years ago entirely corked off the mouth of the Cosna River (my cabin site) , over several consecutive years, completely destroying the coho run that had been there. A few years ago, one of my upstream neighbors spotted a pair of spawners above my place, tho that is the only sighting I am aware of.
Red Dog Mine, north of Kotzebue is a huge zinc and heavy metal mine. Before that was in place, there were no fish living in RD Creek. Since they have been doing mitigation to keep leakage - mined and natural leaching - out of the creek and fish have established themselves without any help. I don't know if it is just residence, or if successful spawning is occuring. I still wouldn't eat them tho.
Pebble Mine Prospect (copper, gold, heavy metals) is a world class catastophe in the making, if it ever proceeds. The potential to decimate (at the very least) the largest salmon-producing watershed in the world is a near certainty to happen. Just one of the clues is a proposed huge toxic tailing lake behind the biggest earth-fill (I think) dam ever constructed (Aswan bigger? ) that has to last virtually forever, on pourus substrate, earthquake zone. The mine itself , by foreign owners, will be played out in 75 years. And the owners will be gone, gone, gone.
There are thousand (or more) year old Roman mining sites in Britain that, every high water, still produce fish kills downstream from "flushing"effect , I am told. I wouldn't eat those fish either- meaning live ones in those streams.
It sounds lije that dam removal was a deliberat clusterf'k, and damn the potential consequences. The river will recover, somewhat at least.
Eventually- who knows how long.
Probably.
Last edited by las; 03/01/24.
