>Can someone help us with determining the basis for which a
>species is determined to be endangered, and to what extent the
>government can infringe upon our recreational rights or wants
>to try and reestablish this species.

I do believe the criteria are listed in the Federal Endangered Species Act. You can also go to the Federal Register, and search for some fish that has been listed as endangered (heres a recent one, the Gulf of Maine DPS Atlantic Salmon) recently, and you will get a major rundown including review of listing criteria.

>
>Who checks the authenticity of their biological opinions?

Its a multi-tiered internal review process. But keep in mind its a public document, so its there for anybody and everybody to see, and challenge if they want. Thats why we have watchgroups who scour places these things are released publicly. Yes, many BO's have been challenged, and many agencies have been brought to court concerning BO's and resulting actions.