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was given to introductions prior to scrutiny from an endangered species perspective (e.g. <br />Werdon 1993ab, USFWS 1995,1997). Nonnative species were not even considered as <br />a factor in the decline of Missouri River fishes in major symposia dealing with status <br />(e.g., Dilliard et al. 1983) and given little attention in other published accounts. As with <br />recovery efforts in the Colorado River and elsewhere there has been a preoccupation <br />with physical habitat change and potential nonnative problems have been largely <br />ignored. <br />The roles and responsibilities of federal and state agencies for protecting natural <br />ecosystems have evolved gradually. Changes in policies of traditional fish and wildlife <br />agencies have occurred in response to a growing perception that biodiversity is worth <br />preserving. The nonnative problem is so serious and pervasive that proposals to extend <br />federal responsibilities, which would have caused considerable controversy with state <br />agencies in the past, now have been met with a majority of acceptance (63% of state <br />game and fish agencies; USOTA 1993). Even so, gaps in federal and state efforts <br />"constitute a serious threat to the Nation's ability to exclude, limit, and rapidly control <br />harmful fish and wildlife" ( USOTA 1993). Recovery efforts for sensitive species in the <br />Missouri River Basin will require the cooperation of federal and state agencies, as well <br />as local governments to reduce the impacts of introduced species. <br />Which species may be placing native Missouri River fishes at risk of decline and <br />potential extinction? A list of candidates is not difficult to obtain. Based on the present <br />introductions, Fuller et al. (1999) provided convincing evidence that every one of the <br />following species could prey upon or compete with the native fish: northern pike, <br />walleye, largemouth and smallmouth basses, salmon, rainbow trout, brown trout, <br />rainbow smelt, and common carp. <br />Why is the decline and loss of native Missouri River fish such an issue that <br />control of nonnatives species is needed? Biological diversity is at risk when nonnative <br />species are introduced. Biological diversity is not simply the number of native species <br />present, but also encompasses the "ecological roles they perform, and the genetic <br />diversity they contain" (Wilcox 1984). Because biodiversity is a characteristic of natural <br />ecosystems, it is not enhanced by the introduction of nonnative species. Biodiversity <br />can be reduced by shifts in the natural patterns of relative abundance (Temple 1990), <br />but there is no doubt that biodiversity is declining on the planet. Such a decline may <br />hold serious and unanticipated consequences for humans (Ehrlich and Ehrlich 1983, <br />Wilson 1992, Ward 1995). <br />Extinction results in an irrevocable loss of biodiversity. Three sets of factors are <br />thought to contribute to extinction: biotic factors, isolation, and habitat alteration (Frankel <br />and Soule 1981). Most extinctions involve a combination of the three sets of factors in <br />which the adverse effects of one set of factors may make the native species more <br />susceptible to the effects of other factors (Frankel and Soule 1981, Soule 1983, Wilson <br />1992). For example, biotic factors such as predation and competition from introduced <br />species may reduce or alter the density, range, and habitat use of a native species. <br />