It’s more a case of not being allowed to use roe. Fish and Game regulations forbid it. Some people fish from a boat, at least on the Waimakariri up from the mouth. The rivers are all braided a couple of km’s up from the mouth, so I think anchoring is pretty much impossible. People do use jet-boats to navigate the rivers in search of suitable pools. What size rivers do you have up there? (Pretty large by our standards I should imagine).
Not sure about egg imitations. I’ve only started fishing salmon this year, and yet to catch one. People use zed spinners almost exclusively at Mackintoshes rocks on the waimak. (Most of the information I’ve got is from reading Ross Millichamp’s book, Salmon FIshing in the South Island)