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reproductively isolated from other conspecific [in the same species] population units, and (2) 

 It must represent an important component in the evolutionary legacy of the species." The 

 federal fish agency designated such a group an "evolutionarily significant unit," or ESU. 



Unfortunately, rather than explain DPS, the new definition has generated a quagmire 

 of confusion and illogic. In the case of Columbia Basin salmon, reproductive isolation, the 

 definition's first criterion, is difficult to evaluate. After over a century of habitat degradation 

 and passage blockage, the few remaining populations are small and greatly fragmental. The 

 isolation we now observe may not be natural, but an artifact of "civilization." Furthermore, 

 countering this isolation is the tendency of salmon to stray into new areas and produce 

 progeny that return there to spawn. In any event, the fact of geographic isolation does not 

 necessarily indicate reproductive isolation. 



The second criterion, evolutionary importance, is vague and highly subjective. Does 

 it refer to genetic material in salmon species descended from salmon of the 1850s? Or to 

 present-day genetic material of importance to the future success of a species? Does it refer to 

 differences in life history and body form? Does it mean something measured in the genes or 

 in the environment? 



Add to these ambiguities the problem of the ESU definition being nearly the same as 

 the species definition. According to NMFS, an ESU is characterized by reproductive 

 isolation and by uniqueness (evolutionary significance), which are the same considerations 

 used in defining a species. Once a salmon population is determined to be an ESU, what has 

 been identified, according to the definition, is more like a species than a group below the 

 species level, such as a distinct population segment. 



Electrophoresis Is Used to Identify ESUs 



In practice, NMFS relies almost exclusively on genetic testing to predict evolutionary 

 significance and reproductive isolation in determining whether a salmon population is an 

 ESU. Using electrophoresis, NMFS scientists differentiate populations by comparing the 

 proportion of individuals in each population according to particular types of proteins. They 

 reason that the larger the differences in these proportions of proteins, the longer the time of 

 reproductive isolation. The agency's scientists infer that populations presumably isolated for 

 a long time are likely to have developed unique characteristics that must be protected. The 

 same results can occur when a common historical population undergoes a series of genetic 

 bottlenecks and population fragmentation as depicted in Figure 1 . 



However, predicting evolutionary significance from minute differences in protein 

 composition is largely speculative: there is no known way to associate biochemical differ- 

 ences with important characteristics, such as length of reproductive isolation or adaptive 

 traits, and no way to correlate the degree to which a population represents a historical 

 population. 



