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Federal Register / Vol. 86, No. 156 / Tuesday, August 17, 2021 / Notices
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reviewers were asked to evaluate the adequacy, appropriateness, and application of data used in the report.
Of the three peer reviewers, two responded with written comments and the third responded informally that they had no comments. All peer reviewer comments were addressed prior to dissemination and finalization of the draft report and publication of these 12month findings.
We subsequently reviewed the report, its cited references, and peer review comments, and believe the report, which informs our 12-month findings, provides the best available scientific and commercial information on the OC
and SONCC Chinook salmon ESUs.
Much of the information discussed below is attributable to the report.
However, in making the 12-month findings determination, we have independently applied the statutory provisions of the ESA, our regulations regarding listing determinations 50 CFR
part 424, and our ESU Policy.
Previous Federal Actions On March 9, 1998, following completion of a comprehensive status review of Chinook salmon O.
tshawytscha populations in Washington, Oregon, Idaho, and California, we published a proposed rule to list seven Chinook salmon ESUs as threatened or endangered under the ESA 63 FR 11482. In this proposed rule, we identified the OC Chinook salmon ESU as comprised of coastal populations of springand fall-run Chinook salmon from the Elk River north to the mouth of the Columbia River 63 FR 11482, March 8, 1998. We did not propose to list the OC ESU of Chinook salmon under the ESA, concluding that the ESU was neither in danger of extinction nor likely to become endangered in the foreseeable future.
On September 16, 1999, following an updated status review for four Chinook salmon ESUs, we published a final rule to list two Chinook salmon ESUs as threatened under the ESA 64 FR
50394. In this 1999 final rule, we identified the SONCC Chinook salmon ESU as composed of coastal populations of springand fall-run Chinook salmon from Euchre Creek, Oregon, through the Lower Klamath River, California inclusive 64 FR 50394, September 16, 1999. After assessing information concerning Chinook salmon abundance, distribution, population trends, and risks, and after considering efforts being made to protect Chinook salmon, we determined in this 1999 final rule that the SONCC ESU of Chinook salmon did not warrant listing under the ESA.

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Evolutionary Significant Unit Analysis The Petitioners requested we delineate and list the OC and SONCC
spring-run Chinook salmon populations as ESUs. As described above, the ESU
Policy requires the consideration of two elements when deciding whether a population unit is an ESU: 1 It is substantially reproductively isolated from other conspecific population units;
and 2 it represents an important component in the evolutionary legacy of the species. The first criterion, reproductive isolation, refers to restricted interbreeding among populations. Such isolation does not have to be absolute, but it must be strong enough to permit evolutionarily important differences to accrue in different population units. Information that can be useful in determining the degree of reproductive isolation includes documentation of fish straying from one population to another, recolonization rates of other populations, the efficacy of natural barriers to migration, and measurements of genetic differences between populations. Each of these types of information has its limitations.
Identification of physical barriers to genetic exchange can help define the geographic extent of distinct populations but reliance on physical features alone can be misleading in the absence of supporting biological information. Documentation of straying between populations can provide information about the movements of individual fish but not the genetic consequences of migration.
Furthermore, measurements of current straying or recolonization rates provide no direct information about the magnitude or consistency of such rates in the past. In this respect, data from the analysis of genetic variation between individuals or groups of fish can be very useful because they reflect levels of gene flow that have occurred over evolutionary time scales.
To be considered an ESU, the population must also represent an important component in the evolutionary legacy of the species. The evolutionary legacy of a species is the genetic variability that is a product of past evolutionary events and which represents the reservoir upon which future evolutionary potential depends.
This second criterion would be met if the population contributed substantially to the ecological/genetic diversity of the species as a whole. In other words, if the population became extinct, would this event represent a significant loss to the ecological/genetic diversity of the entire
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species? In making this determination, the following questions are relevant:
1. Is the population genetically distinct from other conspecific populations?
2. Does the population occupy unusual or distinctive habitat?
3. Does the population show evidence of unusual or distinctive adaptation to its environment?
Several types of information are useful in addressing these questions.
Again, the strengths and limitations of the information will be considered in making the determination. Phenotypic/
life-history traits, such as size, fecundity, and age and time of spawning may reflect local adaptations of evolutionary importance, but interpretation of these traits is complicated by their sensitivity to environmental conditions. Data from DNA analysis provides valuable insight into levels of overall genetic differentiation among populations but in many cases does not contain direct information regarding the extent of adaptive genetic differences. Habitat differences suggest the possibility for local adaptations but do not prove that such adaptations exist.
Methods for Analyzing Genetic Variation Genetic variability within and between populations of Chinook salmon generally falls into two categories:
Neutral and adaptive genetic variation.
Most of the variation in a species genome the sum total of an organisms DNA has no influence on survival or reproduction, and hence is considered to be selectively neutral. Examining patterns of selectively neutral variation among individuals in populations is very useful for understanding the relationships between those individuals and the histories of the populations. For example, neutral variation can be used to estimate the degree of gene flow or interbreeding among different populations, or the familial relationships among specific individuals. Adaptive genetic variation refers to genes or regulatory regions of the genome that have an effect on fitness survival or reproduction. Adaptive genetic variation occurs when certain DNA sequence variants in a population help some members survive or reproduce better than others.
Reproductive Isolation Criterion The 1998 and 1999 coastwide status reviews for Chinook salmon focused on patterns of neutral genetic variation and did not consider differences in run timing adaptive genetic variation alone to be indicative of substantial
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