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" :J72 CHAPTER 15 major threat has been extensive introduction to areas outside their native ranges (Behnke and Zarn 1976); this has led to hybridization and resulted in loss of genetically pure populations, increased competition for food and space, and increased predation on young trout. Allendorf and Leary (1988) considered introgression, dilution of native alleles, the most important effect of introductions of nonnative western trout. Widespread introgression can lead to replacing the diversity of taxa produced by evolution with a single taxon. Such homogenization could result in loss of locally adapted populations and, Jess importantly, outbreed- ing depression (hybrids with reduced fitness). Another factor blamed for the decline of native western trouts is habitat destruction caused by water diversion and removal, channelization, water pollution, and overgrazing of rangeland and damage to streambanks by livestock. Originally, the Apache trout and greenback, Lahontan, and Paiute cutthroat trouts were federaIJy listed as endangered, but they were reclassified as threat- ened to facilitate recovery and management efforts (Behnke and Zarn 1976). Federal recovery plans have been approved for several native western trouts, and management programs have been suc';::essful in rehabilitating certain populations. Status and management of Lahontan and greenback cutthroat trouts were considered in Gresswell (1988); in general, elimination of nonnative trout, reintroduction of genetically pure native stocks, habitat protection and improve- ment, and restricted harvest have been used to enhance populations of these fishes. These actions conform to the steps in a native trout management program outlined by Behnke and Zarn (1976): (1) collection of specimens from suspected genetically pure populations, (2) identification of pure populations by taxonomic study of collected specimens, (3) prot,ection and possible improvement of existing habitat, (4) introduction of native trout into isolated waters devoid of nonnative trouts, and (5) establishment of special-regulation fisheries where applicable. Native western trouts are some of the most aesthetically pleasing fishes in North America and have high sport value. Behnke and Zarn (1976) stated that low-cost quality fisheries can be based on native trouts if they are properly managed and publicized. Therefore, odds favor native western trouts if any of North America's threatened or endangered fishes have a chance of being recovered and delisted. Public awareness and support are needed if native western trouts are to be saved. 15.5 MANAGEMENT FOR ENDANGERED FISHES Fisheries biologists can use many approaches to alleviate threats to rare native fishes. In general, they should strivle to maintain populations of threatened or endangered fishes by recognizing tht:ir status and the importance of preserving biological diversity, contributing to knowledge about them, applying management strategies (and provisions of the ESA), or instructing others on the merits of such actions. When conservation of fishes is possible, Moyle and Cech (1988) recommended the following steps: (1) inventory fishes; (2) monitor habitats, communities, and species; (3) conduct research on best management of resource and nonresource fishes; (4) plan regional management following natural, rather than political, boundaries; and (5) manage fish communities and habitats as units. We see a