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147 



HoLUtt, C.H., and E.O. Wiley, eds. 1986. The zoogeography 

 ot North American freshwater fishes. John Wiley and 

 Sons. Inc.. New York. 866 pp. 



Lee. D.S.. C.R. Gilbert. C.H. Hocutt. R.E. Jenkins. D.E. 

 McAllister, and J.R. Stauffer. Jr. 1980. Atlas of North 

 American freshwater fishes. North Carolina Stale 

 Museum of Natural History. Raleigh. 8.'i4 pp. (Reissued 

 in 1981 with appendix; 867 pp.) 



Matthews. W.J., and D.C. Heins. eds. 1987. Community and 

 evolutionary ecology of North American stream fishes, 

 flniversity of Oklahoma Press. Norman. 310 pp. 



Mayden. R.L.. ed. 1992. Systematics. historical ecology, 

 and North American freshwater fishes. Stanford 

 University Press, CA. 969 pp. 



Mount. R.H.. ed. 1986. Vertebrate animals of Alabam.i in 

 need of special attention. Alabama Agricultural 

 Experiment Station. Auburn University. 124 pp. 



Moylc. P.B.. and R.A. Leidy. 1992. Loss of biodiversity in 

 aquatic ecosystems: evidence from fish fauna.s. Pages 

 127-169 in PL. Fiedler and S.K. Jain. eds. Conservation 

 biology: the theory and practice of nature conservation, 

 preservation and management. Chapman and Hall. New 

 York. 507 pp. 



Page. L.M.. and B.M. Bun". 1991. A field guide to freshwa- 

 ter fishes of North America north of Mexico. Peterson 

 field guide series. Houghton Miffiin Co.. Boston, MA. 

 432 pp. 



Warren, M.L., Jr., and B.M. Burr. 1994. Status of freshwa- 

 ter fishes of the United States: overview of an imperiled 

 fauna. Fisheries 19(1):6-18, 



Williams, J.E., J.E. Johnson, D.A. Hendrickson, S. 

 Contreras-Balderas, J.D. Williams, M. Navarro- 

 Mendoza, D.E. McAllister, and J.E. Deacon. 1989. 

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 special concern: 1989. Fisheries 14(6):2-20. 



For further information: 



Stephen J. Walsh 



National Biological Service 



Southeastern Biological Science 



Center 



7920 NW 7 1st St. 



Gainesville, FL 32653 



Species are composed of genetically diver- 

 gent units usually interconnected by some 

 (albeit low) level of gene flow (Soule I9S7). 

 Because of this restriction in gene flow, natural 

 selection can genetically tailor populations to 

 their environments through the process of local 

 adaptation (Wright 1931 ). 



Because freshwater and anadromous (i.e., 

 adults travel upriver from the sea to spawn) fish- 

 es are restricted by the boundaries of their 

 aquatic habitats, genetic subdivisions may be 

 more pronounced for these vetlebrates than for 

 others. Consequently, managers of programs for 

 these species must realize that the stock (i.e., 

 local discrete populations), and not the species 

 as a whole, must be the units of primary man- 

 agement concern (Kutkuhn 1981). 



Genetic variability in a species occurs both 

 among individuals within populations as well 

 as among populations (Wright 1978). Variation 

 within populations is lost through genetic drift 

 (see glossary; Allendorf et al. 1987), a process 

 increased when population size becomes small. 

 Variation tunoniJ populations is lost when previ- 

 ously restricted gene flow between populations 

 is increased for some reason (e.g., stocking, 

 removal of natural baiTiers such as waterfalls); 

 differentiation between populations is lost as a 

 result of the homogenization of two previously 

 distinct entities (Altukhov and Salmenkova 

 1987;Campton 1987). 



Beyond this loss of genetic variation, mixing 

 two groups can result in outbreeding depres- 

 sion, which is the loss of fitness in offspring that 

 results from the mating of two individuals that 

 are too distantly related (Templeton 1987), This 

 loss in fitness is caused by the disruption of the 

 process that produced advantageous local adap- 

 tations through natural selection. Inbreeding 

 depression, on the other hand, is the loss of fit- 

 ness produced by the repeated crossing of relat- 

 ed organisms. The area of optimal relatedness 

 occurs between inbreeding depression and out- 

 breeding depression. 



Loss of Genetic Integrity 

 Through Stocking 



Many sportt'ish populations are managed by 

 using a combination of harvest regulation, habi- 

 tat manipulation, and stocking. Jurisdiction for 

 these activities falls to federal, state, tribal, and 

 local governments, as well as private citizens. 

 Many resource managers in the past were 

 unaware of the long-term consequences that 

 stocking efforts would have on the genetic 

 integrity of local populations (Philipp ct al. 

 1993). 



Fish introductions can be classified into 

 three types: non-native introductions, in which a 

 given species offish is introduced into a body of 

 water outside its native range (regardless of any 

 political boundaries); stock transfers, in which 

 tlsh from one stock are introduced into a water 

 body in a different geographic region inhabited 

 by a different stock of that same species, yet are 

 still within their native range; and genetically 

 compatible introductions, in which fish are 

 removed from a given water body and they, or 

 more often their offspring, are introduced back 

 into that water body or another water body that 

 is still within the boundaries of the genetic stock 

 serving as the hatchery brood source (Philipp et 

 al. 1993). 



Although non-native introductions may 

 often cause ecological problems for the envi- 

 ronments in which they are introduced, they can 

 also cause genetic problems if they hybridize 

 with closely related native species. Examples of 

 this are the hybridization of introduced small- 

 iiKHith bass {Micwpterits doloinieu) and spotted 

 bass (M punctulcitus) with native Guadalupe 

 bass (M. treciili) in Texas (Morizot et al. 1991), 

 and the hybridization of introduced rainbow 

 trout iOncorhynchus mykiss) with native 

 Apache trout (O. apache: Carmichael et al. 

 1993). The greatest degree of genetic damage, 

 that is, the loss of genetic variation among pop- 

 ulations, is caused by stock transfers, a common 



Loss of 



Genetic 



Diversity 



Among 



Managed 



Populations 



by 



David P. Philipp 



Julie E. Claussen 



Illinois Natural History 



Surrey 



