U&A used to the only place where members of a given federally recognized Tribe could fish as "Indians". To fish outside of U&A, as an Indian, required the invitation of the Tribe having U&A there. Happened all the time, way back when, on the Skagit because it made management easier and protected spawning fish better.

The kicker is that some Indians had non-Indian commercial licenses. As I recall, they could fish in a non-Indian opening but their catch was counted against the Indian share. I think this most often occurred in Fraser sockeye fisheries. This may have changed since I was in the wringer.