Aren’t salmon renowned for returning to the river of their birth? How did they return to a river they couldn’t have used for a generation? Salmon, have you been lying to biologists all this time?
Generally, salmon have a certain amount of variance in the location they migrate to. A certain percentage of the population varies from the birth location and tries new places. This is probably an adaptation that provides the larger population with greater resilience!
This, and they may have released smolts there after removing the dam.
Can’t read the article due to the paywall but…
I’m assuming they’ve been returning to the river but now they can get further up river with the dam removed. Salmon like to spawn in shallow gravel, they’ll find more of that upstream. Dams really change rivers