Maine v. Norton

The National Marine Fisheries Service and the Fish and Wildlife Service (collectively, the services) (defendants), after extensive research and debate, issued a joint policy applicable to all vertebrate populations in 1996 meant to clarify the phrase distinct population segment (DPS) for purposes of listing a DPS as endangered under the Endangered Species Act. Neither DPS nor population was defined by the Endangered Species Act, and there was confusion as to whether political boundaries should be considered in defining a DPS and listing a DPS as endangered. The Fish and Wildlife Service had previously listed populations as endangered based solely on political boundaries without consideration of the significance of the population to the biology of the species, but the joint policy included three elements: discreteness, significance, and conservation status. Under the joint policy, a population segment was discrete if it was either markedly separated physically, physiologically, ecologically, or behaviorally from other populations of the same taxon, or if it was separated by international government boundaries within which there were significant differences in habitat management and regulatory mechanisms that affected conservation. Once a population was determined to be discrete, then the remaining elements of significance and conservation status were considered. Pursuant to the joint policy, the services listed the Gulf of Maine DPS of Atlantic salmon as endangered, and the state of Maine (the state) (plaintiff) challenged the validity of the listing and the joint policy. The state cited Congress’s 1978 amendment to the Endangered Species Act that removed from the definition of species groups of animals “in common spatial arrangement” as proof that Congress did not intend to convey to the services the authority to base listings under the Endangered Species Act on political boundaries.