Aside from certain aboriginal economic opportunities, there is no commercial fishery above the Mission Bridge, which is where Cheam is. The practical reality would be to say, have you engaged in fishing elsewhere? Who knows where it is, but the reality is that there isn't a commercial fishery upstream, so for them that isn't a practical reality. It's to say to go out to the ocean, which is a different thing from trying to accommodate their traditional way of life.
Obviously that brings up all kinds of issues of capitalization for individuals and such things like that. The reality, though, is that the economics just wouldn't work for likely all but one or two members of the band if those individuals were inclined to move away from Cheam. That's the practical issue around the commercial fishery.
I stand to be corrected, but I gather that except for the economic opportunity at Yale, there really isn't anything upstream of the Mission Bridge. Back in the fifties or maybe even the thirties, there might have been something above the Mission Bridge, but not in modern times.