Summary judgment for defendant National Marine Fisheries on suit brought by pesticide manufacturers challenging a biological opinion issued by the defendant to the Environmental Protection Agency under the Administrative Procedure Act, is reversed, the opinion is vacated and the case is remanded, where the opinion that the pesticides would jeopardize the viability of certain Pacific salmonids and their habitat is arbitrary and capricious because it was not the product of reasoned decision-making in that the defendant failed to explain or support several assumptions critical to its opinion.