The opinion of the court was delivered by: Paul L. Friedman United States District Judge
The Endangered Species Act of 1973 affords protection to species that are listed as "endangered" or "threatened."*fn1 In 1978, the gray wolf (Canis lupus) was listed as threatened in Minnesota and endangered throughout the rest of the conterminous United States. On February 8, 2007, the United States Fish and Wildlife Service ("FWS"), an agency within the Department of the Interior, promulgated a final rule revising the wolf's listing status. See 72 Fed. Reg. 6052 (Feb. 8, 2007) (the "Final Rule"). The Final Rule did not affect the listing status of the gray wolf everywhere. Rather, it designated a cluster of gray wolves in the western Great Lakes region as a "distinct population segment," or DPS. It then removed the wolves within the western Great Lakes DPS from the endangered species list. See id., 72 Fed. Reg. at 6066. The Final Rule did not change the listing status of gray wolves outside the boundaries of the western Great Lakes DPS.*fn2
Soon thereafter, plaintiffs The Humane Society of the United States, Help Our Wolves Live, Animal Protection Institute, and Friends of Animals and Their Environment (collectively, "plaintiffs") brought this suit. They challenge the Final Rule under the Endangered Species Act of 1973, 16 U.S.C. §§ 1531 et seq. ("ESA" or "the Act"), and the Administrative Procedure Act, 5 U.S.C. §§ 551 et seq., claiming that FWS violated the ESA and acted arbitrarily and capriciously by simultaneously designating and "delisting" the western Great Lakes DPS.*fn3
On May 30, 2007, the Court permitted two groups to intervene in this matter: (1) the U.S. Sportsmen's Alliance Foundation, the Wisconsin Bear Hunters Association, Scott Meyer and Robert Stafsholt, and (2) Safari Club International, Safari Club International Foundation and the National Rifle Association. These two groups (collectively, "defendant-intervenors") have jointly submitted briefs in support of FWS' position.
Upon careful consideration of the parties' papers, the oral arguments presented by counsel at a hearing on August 4, 2008, and the entire record in this case, the Court concludes that FWS failed to acknowledge and address crucial statutory ambiguities in the course of promulgating the Final Rule. The Court therefore vacates the Final Rule and remands to the agency for further proceedings consistent with this Opinion.*fn4
Gray wolves are the largest wild members of the Canidae, or dog family. See Proposed Rule Designating the Western Great Lakes Population of Gray Wolves as a Distinct Population Segment; Removing the Western Great Lakes Distinct Population Segment of the Gray Wolf from the List of Endangered and Threatened Wildlife, 71 Fed. Reg. 15266 (March 27, 2006). Gray wolves are "frequently a grizzled gray, but . . . can vary from pure white to coal black." Id., 71 Fed. Reg. at 15266. They prey primarily on medium and large mammals, including white tailed deer and elk. Id., 71 Fed. Reg. at 15266.
"Although the gray wolf once roamed across most of North America, by the 1960s the wolf had been almost completely extirpated from the conterminous United States." Pls.' Mot. at 1; see also Defs.' Mot. at 8. In 1978, FWS concluded that "the entire species Canis lupus is Endangered or Threatened to the south of Canada." Reclassification of the Gray Wolf in the United States and Mexico, with Determination of Critical Habitat in Michigan and Minnesota, 43 Fed. Reg. 9607 (Mar. 9, 1978). FWS thus listed the wolf as endangered throughout the United States and Mexico, with the exception of Minnesota, where the wolf was listed as threatened. "Nevertheless, even today the gray wolf remains extirpated across 95% of its historic range."
Pls.' Mot. at 1. As of this writing, the gray wolf is concentrated in two regions: the western Great Lakes region (which includes Michigan, Minnesota and Wisconsin) and the northern Rocky Mountains region (which includes Idaho, Montana and Wyoming). Only the status of the western Great Lakes population is at issue in this case.
A. Endangered Species Act
The Endangered Species Act is "the most comprehensive legislation for the preservation of endangered species ever enacted by any nation." Tennessee Valley Authority v. Hill, 437 U.S. 153, 180 (1978). Congress enacted the ESA "to provide a means whereby the ecosystems upon which endangered species and threatened species depend may be conserved, [and] to provide a program for the conservation of such endangered species or threatened species." 16 U.S.C. § 1531(b).*fn5 "The plain intent of Congress in enacting this statute was to halt and reverse the trend toward species extinction, whatever the cost." Tennessee Valley Authority v. Hill, 437 U.S. at 184. The Department of the Interior is ultimately responsible for implementation of the ESA with respect to terrestrial species. It has delegated primary enforcement authority to FWS, an agency within the Department of the Interior. See Spirit of Sage Council v. Norton, 294 F. Supp. 2d 67, 75 (D.D.C. 2003).
The ESA's protections are triggered when FWS lists a species as endangered or threatened. A species is endangered if it is "in danger of extinction throughout all or a significant portion of its range." 16 U.S.C. § 1532(6). A species is threatened if it is "likely to become an endangered species within the foreseeable future throughout all or a significant portion of its range." Id. § 1532(20). FWS must determine whether a species should be listed as endangered or threatened based upon five statutorily prescribed factors. See id. § 1533(a)(1)(A)-(E) (hereinafter the "listing factors" or the "Section 4(a)(1) factors"); see also 50 C.F.R. § 424.11(c). The listing factors are: (1) present or threatened destruction, modification, or curtailment of a species' habitat or range; (2) overutilization for commercial, recreational, scientific, or educational purposes; (3) disease or predation; (4) the inadequacy of existing regulatory mechanisms; and (5) other natural or manmade factors affecting a species' continued existence. See 16 U.S.C. § 1533(a)(1)(A)-(E).
The ESA further instructs FWS to monitor the status of listed species and, when appropriate, to reclassify or delist species. See 16 U.S.C. § 1533(c). The same five factors that determine whether a species is endangered or threatened also determine whether threats to a species have been diminished or removed to the point that reclassification or delisting is appropriate. See id. § 1533(c)(2); see also 50 C.F.R. § 424.11(d). FWS is required to make listing determinations "solely on the basis of the best scientific and commercial data available."
16 U.S.C. § 1533(b)(1)(A).
2. Distinct Population Segments
The ESA authorizes FWS to list, delist and reclassify "species." When the ESA was enacted in 1973, the term "species" was defined to include species, subspecies or "any other group of fish or wildlife of the same species or smaller taxa in common spatial arrangement that interbreed when mature." Pub. L. 93-205, 87 Stat. 884, 886 (1973). Congress revised this definition in 1978 so that the definition of "species" now includes species, subspecies and any "distinct population segment of any species of vertebrate fish or wildlife which interbreeds when mature." 16 U.S.C. § 1532(16) (emphasis added).
It is common ground for the parties that because the ESA authorizes FWS to list endangered or threatened "species," and because the term "species" is defined to include "distinct population segments," FWS may list a distinct population segment of a vertebrate species even "when the species as a whole is neither threatened nor endangered." Pls.' Mot. at 5; see also Defenders of Wildlife v. U.S. Dep't of the Interior, 354 F. Supp. 2d 1156, 1169 (D. Or. 2005). In this way, the "DPS tool" (as the parties frequently refer to it) permits FWS to "protect and conserve species and the ecosystems upon which they depend before large-scale decline occurs that would necessitate listing a species or subspecies throughout its entire range." Policy Regarding the Recognition of Distinct Vertebrate Population Segments Under the Endangered Species Act, 61 Fed. Reg. 4722, 4725 (Feb. 7, 1996) (the "DPS Policy").*fn6 The central issue in this case is whether FWS ...