CFM,
You have too much time on your hands, a truly dizzying intellect, or both! An American Indian Tribe is a legal entity and a government. So it never "interbreeds" its hunting and fishing rights away. Kind of like the U.S. Constitution, it remains the law of the land, generation after generation. Treaty fishing rights are "owned" by treaty tribes, not by individual persons. A tribal government "franchises" its treaty fishing right to an individual person through a tribal fishing license or permit, much like the state of Washington "franchises" you the privilege of fishing Washington state waters as a sportfisherman through your state fishing license.
While your DNA angle is entertaining, I don't think it's at all relevant to treaty fishing rights. Tribes individually determine who they franchise to exercise their specific treaty fishing right. Some tribes require that you be at least 1/4 blood quantum of that specific tribe in order to be eligible to obtain a fishing permit from that tribe. Others require as little as 1/32 blood quantum to qualify. It's up to the tribe to determine.
As for us all being descended from Eve, what will matter to most tribes is your ancestral lineage from yourself back to 1855 or just prior, which was when the Stevens Treaties were made with tribes in this state. If you were connected by direct relationship with acknowledged tribal members during this time span, you have an excellent case for tribal membership. Otherwise, no.
Oh, and as for a tribe being reduced to 2 or 3 people, whoever is in a tribe with treaty fishing rights has potential access to the full benefits of those rights. This is sort of why numerous north Puget Sound tribes opposed the federal recognition of the Samish Tribe - and previously the Snoqualmie and Stillaguamish Tribes - they recognize that the more tribes there are, the smaller will be each tribe's share of treaty fishing allocations and federal funding for Indian programs like health, education, and housing. Money forms both strange bedfellows and antagonisms alike.
Sincerely,
Salmo g.