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environment exposed to more daylight, primary productiv- ity was greater and food more abundant. Factors other than a greater food supply likely were involved, but the result was a refuge population of pupfish with larger, more brightly-colored bodies and changes in several mensural characteristics (Williams 1977). An unusual, melanistic pop- ulation of threespine stickleback, Gasterosteus aculeatus, from Holcomb Creek, California, was considered to be possibly a new evolutionary form native to the area (Bell 1982), but now is considered to be the result of phenotypic changes in an introduced population. The Holcomb Creek popula- tion's allozyme pattern is identical to that of sticklebacks from the lower Santa Clara River (D. G. Buth, personal communication). Buth (personal communication) hypoth- esizes that the sticklebacks in Holcomb Creek were intro- duced inadvertently with trout from the Fillmore Hatchery located on the Santa Clara River. In other animal groups, most notably birds, the problem of rapid evolutionary change in introduced populations of endangered species is an increasing cause for concern (Conant 1988). Recovery plans list five reasons for introductions: (1) information and education, (2) establishing a genetic reserve or for artificial propagation, (3) use as a biological control agent, (4) supplement existing populations, and (5) establish new populations. A secondary consideration in establishing new populations of certain rare trouts (e.g., Apache trout, Salmo apache, and Gila trout, S. gilae) has been the creation of a sport fishery. Concerns and procedures for conducting an introduction will vary greatly with its intended purpose. Establishing new populations and supplementing existing stocks often are the primary means for recovering many threatened or endangered western fishes. Through 1986, the following numbers of introductions were made for those purposes: Little Kern golden trout, Salmo aguabonita whitei, 43; greenback cutthroat trout, Salmo clarki stomias, 32; Col- orado squawfish, Ptychocheilus lucius, 14; desert pup fish, Cyprinodon macularius, 13; Pecos gambusia, Gambusia nobilis, 32; and Gila topminnow, Poeciliopsis occidentalis, 97. In some circumstances, our ability to introduce endan- gered and threatened species has been facilitated by reg- ulations that enable the designation of "experimental pop- ulation" (see 27 August 1984 Federal Register), designed to lessen local opposition to introducing endangered or threat- ened species. Experimental populations are classified as "essential," or more likely, "nonessential." All experimental populations are classified as threatened, which allows for the species to be taken (i.e., killed or captured) pursuant to special regulations. Further, most nonessential experi- mental populations are not subjected to the rigorous inter- agency consultation requirements of Section 7 of the En- dangered Species Act. Guidelines Within this paper and suggested guidelines, the terms "introduction" and "introduced" are used in their broadest context (sensu Shafland and Lewis 1984) and include any fishes moved by man regardless of whether the organism is moved outside or within its native range. The following guidelines for conducting introductions of endangered and threatened fishes were developed by the American Fisheries Society's Western Division Endangered Species Committee. The guidelines are intended to apply 8 when an introduction of an endangered or threatened fish is proposed to supplement an existing population or to establish a new population. Portions may be useful when introducing fish for artificial propagation, maintenance of a genetic reserve, educational exhibits, or other purposes. Unforeseen circumstances, such as the imminent and un- predicted loss of a population, may require emergency procedures that deviate from portions of the guidelines. Fisheries managers are urged to plan in advance and develop procedures for dealing with such emergencies. Individuals conducting introductions should be familiar with all applicable regulations pertaining to the rare fish(es) in question. Applicable local, state, and federal permits must be obtained. The permitting process often is lengthy, and applications should be submitted as early as feasible. Permits should include procedures for adequate monitoring and preservation of any mortalities. The guidelines are divided into three components: (1) selecting the introduction site, (2) conducting the introduc- tion, and (3) post-introduction activities. 1. Selecting the Introduction Site A. Restrict introductions to within the native or historic habitat whenever possible. For a broadly ranging species, such as the Colorado squaw- fish, the historic habitat includes the mains tern Colorado River and many of its major tributaries, from the Green River of Wyoming to the Gila River of Arizona. On the other hand, a single-spring endemic, such as the Devils Hole pupfish, has a historic distribution of narrowest pro- portions. Any attempt to introduce an endangered or threatened fish outside of its historic range should be viewed with great caution. The historic habitat of a species is herein considered to be those localities from which the species is known plus any interconnected waters from which it could reasonably have occurred. Introductions outside of a species'. historic habitat may be necessary, but should be considered only when all locations within the historic range are unsuitable and/ or unrestorable, when extant historical habitat is clearly threatened with imminent loss, or when the introduction is proposed within a controlled site (such as a hatchery). B. Restrict introductions to a protected site. Any site selected to receive introductions should be secure from imminent or future threats of habitat destruction. In order to protect the habitat, some form of management agreement with the landowner or land management agency is advisable. Placing the site in land dedicated to protecting the species, whether public or private ownership, is pref- erable. C. Restrict introductions to sites where the potential for dispersal has been determined and is acceptable. Depending on the introduction goal it may be advisable to choose sites with little or no opportunity for further dispersal of the introduced population. This is especially true for releases made outside the historic habitat where additional range expansion may not be desired. Conversely, some introductions are intended to expand an existing population within its historic range. In such cases, further dispersal routes may be a prerequisite for site selection. Fisheries, Vol. 13, No.5 j