Avid angler, you are over looking the 2 largest factors that I think IH8XC is basing his statement on (and which he didnt point out).
#1 fraser caught sockeye have a huge distance to travel before they make it to their spawning grounds...some go beyond Prionce George...isnt that 700-800 KM away!!!
#2 the fraser is 19C, its very warm...this in turn causes high metabolic rates in fish and tends to tax and burn more energy stores.
Because coho are most often caught in in their home rivers (vedder/chehalis/etc/etc) AND the water in the fall is cold, the impact of catch and release is far less than that of a fraser sockeye...IF that is what he meant, I would agree.
I don't think there is a difference in survival rates based on the method hooked but the other 2 factors I mentioned probably play a critical role in determining survival rate.
And avid angler, while those fish you release swam away when you released them, that event was taxing for them...who knows how it will affect them by the time they reach hells gate and the fraser canyon???