Here is the relevant portion of the Boldt decision that defines what "in common with" means:
First, the court goes on to clearly state that off-reservation treaty fishing is a right and that non-tribal fishing is a privilege:
"...off reservation fishing by other citizens and residents of the state is not a right but merely a privilege which may be granted, limited, or withdrawn by the state as the interests of the state or the exercise of treaty fishing rights may require." U.S. v. Washington, 384 F. Supp. 312, 332 (W.D. Wash. 1974).
Second, citing to the Puyallup-I case, the court finds a statement there that is contrary to established treaty law...
"Moreover, the right to fish as those respective [usual and accustomed] places is not an exclusive one. Rather it is one 'in common with all citizens of the territory.' Certainly the right of the latter may be regulated [non-Indian fishing]. And we see no reason why the right of the Indians may not also be regulated by an appropriate exercise of the police power of the State." 384 F.Supp at 337, citing Puyallup-I, 391 U.S. 398.
The court goes on to say "This statement seems to say that because a state has police power to regulate fishing privileges [non-Indian fishing] which the state has granted and may limit or entirely withdraw, that it is somehow a legal reason for state regulation of federal fishing rights which are expressly reserved in a treaty which only Congress has authority to limit or modify." Id. at 337.
The court further goes on to outline the obvious fallacy in such an argument and entirely discredit it, citing several cases that support the legal basis for allowing state regulation of state granted privileges while generally prohibiting state regulation of federally granted rights.
I encourage everyone who has any interest whatsoever, much less an opinion, about tribal fishing and state/federal regulation, and the distinction between Indian fishing rights and non-Indian fishing privileges to read the entire case, if they wish. However, the majority of the case is dedicated to delineating which tribes hold the rights and the geographical extent of such rights. The law setting out the nature of the rights is all in the first quarter or so of the case.