MODESTO IRRIGATION DISTRICT; Turlock Irrigation District; Merced Irrigation District; Oakdale Irrigation District; South San Joaquin Irrigation District; Stockton East Water District, Plaintiffs-Appellants, v. Carlos M. GUTIERREZ, in his official capacity as Secretary of Commerce; D. Robert Lohn, in his official capacity as Regional Administrator of the Northwest Region of NMFS; National Oceanic and Atmospheric Administration, a federal agency; Conrad C. Lautenbacher, Jr., in his official capacity as Administrator of National Oceanic and Atmospheric Administration; William T. Hogarth, in his official capacity as Assistant Administrator for Fisheries of NMFS; National Marine Fisheries Services, a federal agency within the Commerce 12403 Department; Rodney McInnis, in his official capacity as Regional Administrator of the Southwest Region of NMFS, Defendants-Appellees, and Center for Biological Diversity; Delta Fly Fishers; Federation of Fly Fishers; Northern California Council of Federation of Fly Fishers; Trout Unlimited, Defendants-Intervenors-Appellees.

Plaintiffs, Modesto Irrigation District and other irrigation and water districts, formed a coalition in 2006 to file this suit under the Administrative Procedure Act ("APA"). Largely, Plaintiffs contended that, in listing the steelhead—a type of Pacific salmon—as "threatened" under the Endangered Species Act ("ESA"), the National Marine Fisheries Service ("NMFS") violated both the ESA and APA. More specifically, Plaintiffs averred that (1) listing the steelhead as a distinct species under the ESA violated the Act because the steelhead and rainbow trout interbreed and (2) the NMFS violated the APA by failing to adequately explain its decision to adopt a new policy for classifying the fish. The United States Court of Appeals, Ninth Circuit, disagreed with both of Plaintiffs’ contentions and affirmed the ruling of the United States District Court for the Eastern District of California. As to the Plaintiffs’ first argument, the court noted that while the steelhead and rainbow trout do interbreed, Congress, in enacting the ESA, did not intend to create a rigid limitation on an agency’s discretion to define the "statutorily undefined concept" of a "distinct population segment" ("DPS"). Hence, "distinct population segment" is an ambiguous term. In fact, by incorporating such language into the ESA and then declining to define it, Congress intended to provide agencies such as the National Marine Fisheries Service with discretion in deciding what comprises a "distinct population segment." Finally, as to Plaintiffs’ second and last contention that the APA failed to adequately explain its decision to adopt a new policy for classifying the fish, the court again disagreed. The Court condidered that NMFS engaged in a careful decision-making process and provided a sufficient explanation for its decision to apply the DPS policy. Particularly, the NMFS was not arbitrary or capricious in changing its policy in order to protect the steelhead, as the record contained "ample support" for the reasons it implemented the new policy.