Yes I have heard the same thing, and know the rivers they most likely show up in first. Zipperlips for sure
If you can find these fresh silver brutes you can have some unbelievable fishing, but landing them is a whole other story. I have gotten bloody knuckles and burned fingers a few times from these guys. 20 lb test leader is many times not enough. We left the river a couple of times 0 for 20 something each, and walked out saying what a great day that was, Alaska could not be better.
The lake michigan Chrome Warriors are preparing for battle with us now, schooling closer to the river mouths. Charter boats seem to be starting to get them regularly now.
Anytime from mid august on there will be fishable numbers in the rivers from my experience. However you have to know where to find them in each river, thats the big trade secret one had to develop through on the river experience.
I am not giving that out on the internet for sure.