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-:.> -!:-. OO~42n seasons of the year, spring and fall. The question is whether a single run in a particular creek shows sufficient genetic nov- elty to merit protection under the ESA. The Kla. math River has a half.dozen major tributaries, and these arc fed by well over 100 streams. Are we prepared to accept the cost of protecting hundreds of subunits of this one species within a single river system? The debate over salmon in the Pacific Nonhwest has yielded claims of the number of protectable stocks ra1lging from dozens to thousands, and bureaucrats are twisted in knots over where the truth lies. The sad fact is that, twenty years into endangered species protection, we still do not have a elear defini- tion of what it is we are trying to protect. The ESAstates, "the term 'species' includes any subspecies of fish or wildlife or plants, and any distinct population segment of any species of vertebrate fish or wildlife whieh interbreeds when mature." 16 U.S.c. S; 1532(16).1t seems clear that in adopting this definition Congress intended to protect not only true species but also significant genetic varieties within species, particularly within venebrate animal species. The definition of "significant" is not nearly so clear. The National Marine Fisheries Service (NMFS), which has responsibility for anadro- mous fish, published a rule that labeled the minimum taxonomic unit wonhy of protection an evolutionarily significant U1lU. 56 Fed. Reg. 58,612 (Nov. 20,1991). To qualify as an ev. olutionarily significant unit a population must satisfy two criteria: it must be reproductively isolated from other populations and it must rep. resent an important component in the evolu- tionary legacy of the species. Are the different salmon stocks in the Kla- math River basin evolutionari Iy significant units? Because one criterion is gene flow isolation, the question might be rephrased to ask if all these stocks are genetically isolated. To answer this question, one must know what level of genetic isolation is sufficient to qualify a population for evolutionary significance. This has not been es- tablished, although the NMFS has refused to in- sist upon absolute barriers to gene flow. A5 for the second criterion, no serious attempt has been made to define evolutionary legacy and cer. tainly not importance in this context. The cur- rent situation for anadromous fish is that one term has been replaced by several orher terms. all equally ill.defined. The U.S. Fish and Wild- life Service (FWS) is no closer to defining a protectable unit on the terrestrial side. It wres- tled with the problem in the process of listing the marbled murrelet: When considering whether [Q list a population segment, the Service assesses the bioJogicalsig- nificance of the population segment to the sub- species as a whole. Thus, threats to a population will vary depending on which segment of the species' range is being considered. Addition- ally. one segment may be significantly threat- ened, but the biological importance of that segment {Q the species as a whole may not be considered significant to the listing of a species. 57 Fed. Reg. 33,478. 33,479 Ouly 29, 1992). 5ignlfic07lt segments sound much like ev- olutionarily significant units and share with them the same weakness, the lack of objective criteria by which to assess significance. Com- pounding the confusion, Richard N. Smith, dep- uty director of the FWS, suggested to the U.S. Court of Appeals for the Ninth Circuit in Mar- bled Mltrrelet v. Lltjan, C.A. No. 92-36705, that at least one of the following four criteria be met for a population to be recognized as a distinct population segment: I. it is significantly isolated from other mem- bers of the same species or subspecies (i.e., it rarely interbreeds with other populations); 2. it occupies an ecosystem that is in danger of destruction throughout all of (sic) a significant portion of its historical distribmion, and the species or subspecies is not present in sur. rounding ecosystems; 3. it is the only occurrence of a species or sub- species within Unired States jurisdiction; or 4. it can be defined by geo-political boundaries that delineate an area representing a significant portion of the species' or subspecies' range where existing legal protection is inadequate to ensure its survival. Although space is inadequate to analyze these criteria in detail, they reveal two distinct patterns. FWS has yet to figure out what consti- tutes a distinct population segment, and it con- fuses the biological aspects of defining a segment with its regulatory responsibilities to- ward the segment, once defined. The source of this problem is not bureau- cratic incompetence. The ESA asks something of biologists that they have not traditionally been prepared to provide: a clear definition of what constitutes an important variant within a spe- cies. The legal and policy communities must understand that with the exception of (fue spe- cies all taxonomic units in biology are some- what arbitrary. The discussion of what makes a . subunit within a species, be it a subspecies, race, ecotype, variety, or stock, is such a dura- ble source of dispute among systematic biolo. gists that scientific consensus may never be achieved. Biologists will advocate either of twO al- ternative paths to solve this problem. The first is the traditional approach of evolutionary bi- ology. which is to find the differences between populations of a species and discover which of NR&E/SUMMER 1993 The sad fact is that, twent)' years into enda1lgered species protectio1l, we still do not bave a clear definition of what it is we are tryi1lg to protect. 7