Cupo is right on this one.
Page 26 of the regs specifically says "All freshwater areas are closed to FISHING for SALMON... unless listed as open in the special rules."
"Fishing" in this rule includes both retention and CNR. Think about it? How can one argue that it is OK to CNR (i.e., no retention) in closed waters, when in fact you have to perform the active act of "fishing" in order to perform CNR?
Whether it is legal to CNR for salmon in closed waters has been debated before in this board and in other boards. The general position has been that it is NOT permissible to do so. I personally would not take the risk.
Here's the bottom line folks: If you are fishing in an area that is closed to salmon fishing, using your Vibrax spinner with the 2/0 hook, and then the warden approaches you and asks: "What'ya fishin' for?" and then you reply: "Salmon but I am releasing all of them." Then you are going to get a big fat ticket.
However, if you are fishing the same water with your garden worm and size 6 hook and 4lb test line, and you say to the warden "I'm fishing for trout, but these stupid salmon keep hitting my bait, and I am releasing them anyways", then you should be OK.
Sorry to rain on the parade...