There's something fishy going on here: a critique of the National Marine Fisheries Service's definition of species under the Endangered Species Act.

• Author: Rohlf, Daniel J.
• Position: Endangered Species Act at Twenty-One: Issues of Reauthorization

1. INTRODUCTION

   Even after all of the controversy and litigation spawned by the federal Endangered Species Act of 1973 (ESA),(1) it is ironic that over twenty years after its enactment agencies which administer the Act lack a clear sense of what "species" they should protect. The National Marine Fisheries Service (NMFS), which together with the U.S. Fish and Wildlife Service (FWS) is charged with implementing the statute,(2) recently attempted to define populations which qualify for listing.(3) In a recent law review article,(4) attorneys with NMFS and the National Oceanic and Atmospheric Administration (NOAA) explained the agency's rationale for its definition of a "distinct population segment" which qualifies for listing under the ESA's definition of species.(5) After providing relevant background, this article argues against NMFS' approach to this issue, and criticizes the reasoning which Gleaves employs to justify the agency's notion of what constitutes a species eligible for ESA protection. It also explores how FWS and the federal courts have wrestled with the same question and examines a draft policy issued by FWS in 1992. The article concludes that FWS' suggested approach better comports with the current state of biological sciences and with the policy objectives Congress sought to further through the ESA

2. BACKGROUND

   Although characterized as the "pit bull of federal environmental statutes,"(6) the ESA is as meek as a kitten unless an imperiled creature appears on the statute's lists of threatened and endangered species. The law offers virtually no substantive protections to organisms not listed,(7) a fact which focuses tremendous interest and controversy on the ESA's listing process.(8) In order to qualify for listing, FWS or NMFS must find that a group of organisms constitutes a species, and determine that the species is endangered or threatened. The ESA defines a species to include subspecies and "distinct population segments" of vertebrate fish and wildlife.(9) Neither the Act nor its implementing regulations define the terms subspecies or distinct population segment. The statute defines an endangered species as a species in danger of extinction throughout all or a significant portion of its range.(10) A threatened species is one likely to become endangered in the foreseeable future.(11)

   For much of the ESA's history, providing protections to groupings below the species or subspecies levels was relatively uncontroversial.(12) The current list of protected species includes many populations of species which as a whole do not necessarily face extinction. These populations are usually defined by geographical occurrence.(13) For example, grizzly bears are listed as a threatened species in the contiguous United States, whereas grizzlies in Canada and Alaska are not listed.(14) However, controversy over ESA protection for runs of Pacific salmon in the Pacific Northwest prompted NMFS and FWS to reassess their authority to list distinct population segments. Historically, fisheries managers differentiated salmon populations based on run timing and geographical occurrence.(15) In 1990, Indian tribes and environmental organizations filed several petitions requesting listings of various salmon populations based on these historic management classifications.(16) These petitions, which almost overnight raised the issue of salmon conservation to a level of controversy approaching that surrounding efforts to protect northern spotted owls, prompted NMFS to closely examine its authority under the ESA to list groups of organisms other than entire subspecies and species.

   NMFS' deliberations resulted in the agency formulating a salmon-specific definition of the phrase "distinct population segment" within the ESA's definition of species. According to NMFS, only an "evolutionarily significant unit" (ESU) of a broader salmonid species qualifies as a distinct population segment eligible for protection.(17) A population constitutes an ESU if it meets two criteria. First, a population "must be substantially reproductively isolated from other conspecific population units."(18) This criterion does not require that reproductive isolation be absolute, but the population's isolation must be "strong enough to permit evolutionarily important differences to accrue in different population units."(19) Evidence of such isolation, according to NMFS, can be gleaned from movements of tagged fish, recolonization rates of other populations, evaluations of the efficacy of natural barriers, and measurements of genetic differences between populations.(20) Second, a population must "represent an important component in the evolutionary legacy of the species."(21) NMF's characterizes a species' evolutionary legacy as "the genetic variability that is a product of past evolutionary events and which represents the reservoir upon which future evolutionary potential depends."(22) Thus, in order to satisfy the second element of the ESU test, a population must "contribute[] substantially to the ecological/genetic diversity of the species as a whole."(23) Indicators of such a contribution include genetically-driven physical characteristics and data from scientific tests which analyze genetic make-up.(24)

   NMFS' ESU concept has significantly influenced the agency's listing decisions. While NMFS has found some salmon runs to qualify as ESUs, the agency has used this concept to reject ESA protection for other runs. For example, petitioners asked the agency to protect separately spring and summer runs of chinook salmon in the Snake River.(25) However, citing "the possibility of substantial levels of gene flow" between the two runs, NMFS lumped these stocks together as constituting a single ESU.(26) Finding that this ESU was experiencing an alarming decline, NMFS listed Snake River "spring/summer chinook" as a threatened species.(27) The agency also used its ESU concept to deny ESA protection to a winter steelhead run in Oregon's Illinois River. Citing insufficient data to demonstrate that these fish were genetically distinct from other nearby steelhead populations, NMFS threw out a petition to list the Illinois winter run.(28) More recently, utilities opposed to a pending petition to list mid-Columbia summer chinook acknowledged that numbers of summer chinook have declined, but argued strenuously against protecting this stock because of its alleged genetic similarities to the more numerous fall chinook run.(29)

   Although NMFS published its definition of distinct population segment as a "policy" specific to Pacific salmon rather than as a regulation formally interpreting the ESA, the agency's ESU concept clearly carries potentially broad implications for all listings under the statute. It seems unlikely that NMFS would abandon its ESU policy when the agency makes listing decisions involving organisms other than salmon; NMFS drafted the policy and its technical justification in terms sufficiently broad to readily apply to vertebrates other than salmonids. NMFS' policy could also influence FWS, which itself has struggled with the scope of its listing authority in recent years.(30) Adding to the uncertainty over this issue, FWS in 1992 issued a draft policy interpreting distinct population segment in a manner dramatically different from NMFS' ESU approach, but days later made a significant listing decision on the basis of ESU concepts.(31) NMFS and FWS are currently attempting to formulate a joint definition of groupings eligible for ESA protection.(32) This issue has also generated tremendous interest in legal and scientific circles.(33) Ultimately, a decision on the meaning of distinct population segment may fall to Congress; resolution of this issue is widely mentioned as an integral part of the Act's pending reauthorization.

3. INTEGRATING POLICY AND BIOLOGY

   Formulating and implementing policy involving biodiversity conservation presents Congress and administrative agencies with tremendous challenges. First, policymakers must consider and accurately employ biological concepts in order to devise sensible regulatory schemes. On the other hand, however, administrative agencies with a great deal of technical expertise must implement statutory directives in a manner which carries out lawmakers' policy aims. Further, lack of scientific certainty often substantially complicates both of these processes. The ESA's protection for distinct population segments serves as an excellent example of the steps--and difficulties--involved in integrating law and biology.

   In giving NMFS and FWS authority to list groupings below the subspecies level, Congress was responding to both scientific and policy considerations. When they created the ESA, lawmakers stressed the importance of maintaining genetic diversity, and astutely recognized that populations can play a crucial role in the persistence and evolution of a species as a whole.(34) However, Congress later chose to afford agencies authority to protect only vertebrate populations.(35) Since no biological reasons exist to distinguish between vertebrates and invertebrates with respect to the role genetic variability and healthy populations play in maintaining an entire species, Congress clearly excluded invertebrates from the definition of distinct population segment as a matter of policy.(36)

   Congress makes these types of policy choices as a matter of course, but faces significant problems in dealing with scientific issues. Humans' limited understanding of the planet's biosphere makes it devilishly difficult to integrate law and biology. Part of this difficulty stems from the differences in the processes of making laws and gaining scientific knowledge. While biologists' understanding of other species and ecosystems continually evolves hopefully increasing), federal law remains static until Congress finally changes it. Mindful of this problem, as well as of their limited scientific expertise, legislators have devised...