Harri,
Thanks for posting that explaination..but i still don't get it. The river had natural spawning, presumably it also had other species in the river, all spawning on existing gravel beds.
They move 640 salmon upstream, presumeably a fraction of what was in the river.
They then blast the dam in one go, releasing thousands of tons of silt into the river, more than likely destroying the spawning beds down stream and sweeping other fish down stream, and also probably destroying all sorts of wildlife in the process.
Maybe I am just a bit unusual, but I would have though openning the dam gradually, lowering over a period of months and not releasing a deluge of silt into the river would have made far more sense.
Just a thought. I hope they don't try that on the Peterculter dam!