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7/14/2009 5:01:47 PM
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UCREFRP
UCREFRP Catalog Number
8108
Author
Dizon, A. E., C. Lockyer, W. F. Perrin, D. P. Demaster and J. Sisson
Title
Rethinking the Stock Concept
USFW Year
1992
USFW - Doc Type
A Phylogeographic Approach
Copyright Material
YES
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<br />Dizonettd. <br /> <br />Qualified Phytogeographic Taxa <br /> <br />The manner in which such a phylogeographic classifi- <br />cation of any given population is made and the confi- <br />dence in such a decision depends on the amount of <br />information available. We suggest that this information <br />be appended to the phylogeographic taxa using a short- <br />hand method (Fig. 3). A shorthand notation is necessary <br />because resource management documents usually con- <br />tain extensive lists of stocks that have received or are <br />being considered for separate management status. Using <br />this approach, reference to a given management unit <br />would carry with it information regarding its phylogeo- <br />graphic structure (category type) and the data from <br />which the decision was made (criteria basis). <br />The phylogeographic category is designated by a Ro- <br />man numeral (I, II, III, and N; Fig. 2). The proxy infor- <br />mation with which decisions regarding the population <br />are made is designated as "a" (distribution and move- <br />ment), "b" (population responses), "c" (phenotypic dif- <br />ferences), and "d" (genotypic differences). A population <br />would be designated by phylogeographic category and <br />decision criteria, for example, II albed. Letters to the left <br />of the solidus represent data for "lumping" and those to <br />the right, data for "splitting" the group (Fig. 3). <br />A population that has a high probability of being an <br />ESU is immediately apparent from its phylogeographic <br />category. The degree of confidence in such a classifica- <br />tion is indicated from the type of information that was <br />marshalled to make the decision. Situations where infor- <br />mation was lacking or equivocal could be informative <br />from a management sense. In cases where information <br />, regarding one or more of the criteria was unavailable, <br />the letter designation would not be present (perhaps a <br />dash could be substituted), or the same letter could <br />appear on both sides of the solidus if information was <br />equivocal or unresolvably contradictory, A stock desig- <br />nation of type III dad would probably stimulate more <br /> <br />PhyIogeoghraphlc <br />category <br /> <br /> <br /> <br />media <br /> <br />Rethinking the Stock Concept <br /> <br />31 <br /> <br />aggressive management than one _~esignated as III da, <br />and such a designation would help focus additional re- <br />search efforts. Where there is clear geographic separa- <br />tion but extensive overlap of mll!gins tempocally, as in <br />type III, we might wish to denote this fact by indicating <br />the stock as III ala. In another example, where popula- <br />tion response is to be included in the stock criteria, <br />there might be no difference between demographic pa- <br />rameters and pollutant and parasite loads, but clear dif- <br />ferentiation between dialects, The stock that perhaps <br />might be type II might then be designated as II bib. If all <br />aspects showed clear differences, then the category <br />would be II /b. <br />In the appendix, we have chosen a marine mammal <br />species to illustrate the procedure. The minke whale <br />(Balaenoptera acutorostrata) has populations with re- <br />lationships demonstrating each of the four phylogeo- <br />graphic categories. Current biological information on <br />the minke whale is provided in detail, covering as much <br />ground as possible under each of the four criteria. Clas- <br />sifications are suggested for the various putative stocks. <br /> <br />The Decision Process <br /> <br />TI1is proposed system of phylogeographic classification <br />of course addresses only single-species considerations. <br />Because of ecological phenomena such as predator-prey <br />interactions, the existence of keystone species and spe- <br />cies guilds, etc., a population may be important beyond <br />its qualifications, or lack thereof, as an ESU; these factors <br />must also be considered in deciding what should com- <br />prise a management unit. <br />It is most important that the phylogenetic classifica- <br />tion be carried out as an exercise separate from and <br />prior to consideration of the socioeconomic and polit- <br />ical factors that inevitably influence the management <br />status of a population, and, further, potential conflicts of <br /> <br /> <br />Available <br />Infonnation <br /> <br />Figure 3. A shorthand method for qualifying stock type using Pbylogeograpbic categories and information re- <br />garding the criteria used to make sudJ qualifications. <br /> <br />1,":0::"" <br />~, <br /> <br />, , <br /> <br />Coasc:rvadOD Biology <br />Volume 6, No, I, Man:b 1992 <br />
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