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Great Lakes Sport Fishing Council, pers. comm., <br />1992). Rainbow trout fishing in States like <br />Virginia, Colorado, or Pennsylvania constitutes a <br />nonindigenous species use. The millions of <br />anglers who fish for largemouth bass <br />(Micropterus salmoides) outside its native range <br />(e.g. in Oregon, California, Arizona, and many <br />other States) clearly depend on a nonindigenous <br />species. These and other species have become <br />major components of the current sport fishing <br />programs in most States. Past management prac- <br />tices have thus created the expectation that such <br />fisheries will continue to be available. <br />Nonindigenous species have also been used in <br />situations where human activity has so altered an <br />ecosystem that it can no longer support indige- <br />nous species. In these highly altered ecosystems, <br />introduced species may play a role in maintaining <br />ecosystem productivity and in providing social <br />and economic benefits. For example, habitat <br />alteration that restricted movement, coupled with <br />siltation and elevation of stream temperatures led <br />to the demise of native grayling (Thymallus arcti- <br />cus) populations in stream habitats in northern <br />Michigan. The ecosystem was so altered that <br />attempts to reintroduce similar grayling strains <br />were unsuccessful. Introduced rainbow trout <br />now provide a productive fishery until such time <br />as the habitat may be restored. <br />ASSOCIATED RISKS: <br />The above accounting of some of the uses of <br />nonindigenous species illustrates that they must <br />be recognized as ongoing activities of significant <br />socio-economic importance, but does not sug- <br />gest that these and other species have not also <br />been the source of significant economic and <br />environmental impacts. To assess the impact of <br />introductions generally, the Office of Technology <br />Assessment (OTA) contracted for a series of <br />studies on different types of introduced species. <br />The studies reviewed 112 species of introduced <br />fish and 77 species of introduced mollusks. They <br />concluded that 45 species of fish and 32 species <br />of mollusks have had harmful economic or envi- <br />ronmental effects. In some instances introduced <br />species had both beneficial and harmful effects. <br />Although some of those who submitted com- <br />ments on the proposed report expressed the view <br />that unintentional introductions constitute the <br />major problem, OTA concluded that intentional <br />introductions are as likely to cause problems as <br />unintentional introductions. Their definition of <br />intentional introductions was narrower than that <br />used in this report. As intentional introductions, <br />they only considered species deliberately released <br />into the natural environment. For fish, 35 of 76 <br />intentional introductions and 10 of 26 uninten- <br />tional introductions had some harmful effects. In <br />the case of mollusks, five of ten intentional intro- <br />ductions and 27 of 67 unintentional introduc- <br />tions had harmful effects. In the case of <br />intentional introductions, such figures may indi- <br />cate apoor selection of species and inadequate <br />screening (OTA 1993). <br />For many cultured species, effective containment <br />is becoming an increasingly important aspect of <br />culture techniques. For example, because tilapia <br />are aggressive and compete with indigenous <br />species for spawning sites and space, they have <br />been prohibited from introduction into several <br />States (Parker 1989). Shelton and Smitherman <br />(1984) suggested that "escape is virtually <br />inevitable" in fish culture. Similarly, Welcomme <br />(1988) concluded that species used in aquacul- <br />ture "eventually escape" and that "any introduc- <br />tion made for aquaculture must be thought of as <br />a potential addition to the wild fauna." It will be <br />important to both private industry and public <br />agencies for all forms of aquacultura] facilities <br />(e.g., hatcheries, production ponds, holding <br />facilities) to develop more effective containment <br />strategies. If this impression of the inevitability of <br />escape and any regulatory trend toward prohibi- <br />tion of potentially deleterious species are to be <br />reversed, it will be necessary to demonstrate the <br />feasibility of longterm escape control. <br />Demonstration of such control may also go a <br />long way toward easing decisions made under <br />any current or future permit system. <br />The presence of an introduced species in an open <br />environment necessarily involves an impact of <br />some kind. 1n a recent text on "biological po~lu- <br />tion," Courtenay (1993) summarized that "... <br />every introduction will result in impacts to native <br />biota, which may range from almost nil to major, <br />including extinction with time." Nonindigenous <br />species may affect indigenous species by compet- <br />ing for resources, preying on native fauna, trans- <br />ferring pathogens, or significantly altering <br />habitat. The introduction of a nonindigenous <br />species may work synergistically with other fac- <br />tors, such as water diversions or pollution, to <br />alter the population and distribution of indige- <br />nous species. The factors are often cumulative <br />and/or complementary. For example, habitat <br />7 <br />