CM -
There is little doubt that ESA applies to the tribes (the co-managers have to get take permits). However the rub has been and will continue to be that NMFS considers their federal responsibilities to preserve tribal fishing rights to have equal footing with their ESA responsibilities (two # 1 priorities if you will).

When pushed the Feds consistently opt to favor the tribal needs - look at the allowable ESA impacts on the upper Columbia where approximatley 80% of the impacts go to the tribes and the rest to the non-tribal fishers.

As you suggest might not be an issue many folks would want to push - if you can live with the potential answer don't ask the question.

Tight lines
Curt