Not necessarily just the opinion of one biologist, but a thorough review by biologists that results in a government decision, more than an opinion.
A “BiOp” in policy short-hand, this is the result of the consultation between agencies. The action agency (BOEM, in our previous example) asks for input from the regulatory agency (NMFS) on a specific action or project. The regulatory agency does their homework and gives the action agency their “Biological Opinion” – if the action will jeopardize a listed species or destroy their critical habitat.
If it’s a yes, the regulatory agency suggests “Reasonable and Prudent Alternatives” – other ways of carrying out a project that will not cause jeopardy. If the answer is no, then “Reasonable and Prudent Measures” are suggested, which would reduce any accidental impacts that might happen.
For example, to avoid accidentally knocking something over by playing with the dogs inside, I’m going to apply the Reasonable and Prudent Measure of taking them outside to run around. Sometimes, however, the government says it’s OK to let the dogs run inside and risk knocking things down and that’s where groups like WDC step in to challenge the BiOp.
For example, WDC and its partners have previously challenged BiOps when NMFS decided that certain fisheries known to entangle and kill endangered right whales would not jeopardize the survival of right whales. Sometimes those challenges go to court and the court has required NMFS to review and redo the BiOp.