Lohn

We are asked to decide whether the federal government’s policy for listing killer whales under the Endangered Species Act is invalid.

I

The Center for Biological Diversity (“Center”), along with eleven co-petitioners not parties to this appeal, petitioned the National Marine Fisheries Service (“Service”) to list the Southern Resident killer whale (“Southern Resident”) as an endangered species under the Endangered Species Act (“ESA”), 16 U.S.C. §§ 1531-1544 . Applying its Distinct Population Segment Policy (“DPS Policy”) for listing endangered species under the ESA, the Service issued a proposed ruling that concluded listing the Southern Resident was “not warranted” because the Southern Resident was not “significant” to its taxon. See 67 Fed. Reg. 44,133 (July 1, 2002).

The Center challenged the Service’s proposed determination in district court. On cross-motions for summary judgment, the district court granted in part and denied in part. Ctr. for Biological Diversity v. Lohn, 296 F.Supp.2d 1223, 1243 (W.D.Wash.2003). The district court concluded that the DPS Policy was not contrary to congressional intent regarding the ESA, and that it was a reasonable interpretation…