The reason the regs say to release chums on the Skagit this year is pretty simple.

It is not a secret nor is it rocket science.

Homer - Ask Polly about it. She knows!
Then post the answer here to end the speculation.

I would but I'm kinda full of crap right now so I better go take a dump. :p

BTW: neither the SCL nor the PSE dams were letting water through when the redds were de-watered and they were re-watered soon enough to prevent any loss.