alt Hacker NewsSilly question but if I remember correctly salmon go back to reproduce where they spawned. This suggests that once access is cut up a river, that location loses its salmon (can’t get there, so they don’t reproduce?)
Do they artificially reintroduce the salmon once access is restored or does that “neighbourhood” of salmon somehow survives and keeps trying every year ?
Replies
Some small percentage of fish go to different streams rather than returning to their “home” stream. There’s also hatcheries that release fish raised elsewhere to try and restore runs without enough fish to sustain a healthy population.
Source: I used to volunteer at one of those hatcheries raising endangered coho and releasing them in the spring. I spent a lot of time chilling in the bushes with NOAA scientists talking about fish.
I'm not an expert, but what I understand is Salmon return to the stream, not the place. They know the stream by smell (that is the minerals and other impurities in the water). They are navigating to what smells like home, every time a new stream enters the one they are in they decide which branch to take. This tends to take them to where they spawned, but there are a lot of errors in each choice.
Some get lost or stray. It is natures back-up plan.
Stocking can give it a faster kickstart though
salmon mostly prefer to return to there natal habitat, but there are a significant number of fish that are wanderers and colinists, so there are now salmon runs happening in far northern watersheds that have only recently become warm enough for juvinile fish. also, fish from clutches of eggs that are transplanted to streams with no fish, become native, which points to the homing instinct bieng re attached with each generation rather than hard coded geneticly, though that may happen in some sub species
IANAS but my understanding is they keep going upstream - while there's current to push against them - as an instinctual response. I believe water temperature also plays a role.
Salmon hatcheries also artificially boost the quantity of salmon in the stream.
If a salmon hatchery released salmon at the base of a dam, when the fish return and the dam was now gone, they'd just keep going.
However, there's more to it than this, because dammed rivers lacking salmon hatcheries have seen salmon runs start once the dams are removed.
I don't think the old adage that salmon will only return to their original spawning grounds is the whole story.