Ohi Li\ini: Rcsoiiivc.s — Nuii-iuilhe Species 



43.1 



bass, American shad, yellow perch, catfish, 

 bullheads, sunfish. black bass, and crappies. 

 Most of these introductions resulted in estab- 

 lished populations that still persist today. At this 

 same time brown trout, tench, and carp were 

 being stocked throughout the country. A resur- 

 gence of stocking occurred around \^)50 when 

 many state agencies began stocking game tlsh. 

 The popularity of home aquaria and the avail- 

 ability of foreign fish have also contributed to 

 an increase in the number of species introduced 

 in the past 40 years (Courtenay and Williams 

 1992: Fig. 2). 



The Future 



The presence of nonindigenous fish will 

 continue to alter U.S. aquatic resources. These 

 species compete with or prey on native game 

 and nongame fish, often with sexere negative 

 effects on aquatic ecosystems. Nonindigenous 

 fish that survive the initial introduction and sub- 

 sequently become established are often tolerant 

 of adverse or altered environmental conditions, 

 including habitat disturbance. This tolerance 

 has been used to justify nonindigenous fish 

 introductions rather than to restore disrupted 

 environments. The environmental tolerance of 

 nonindigenous fish combined with increasing 

 habitat disruption in streams and lakes assures 

 their continued dispersal into formerly unoccu- 

 pied areas. If the introduction and establishment 



of nonindigenous fish continue at their present 

 rates, distribution and survi\al oi' native aquatic 

 organisms could be drastically affected. These 

 introductions can also profoundly change bio- 

 logical diversity and composition of habitats 

 and ecosystems, which could result in substan- 

 tially increased rates of extinction of native 

 aquatic species. 



References 



Boydstun. C.P.. and A. Benson. 1992. Nonindigenous report 

 (1992:1): zebra mussel (Dreissena polyniorpha) sites in 

 the United States and Canada. National Fisheries 

 Research Center. Gainesville. FL. 10 pp. 



Courtenay. W.R.. and J.D. Williams. 1992. Dispersal of 

 exotic species from aquaculture sources, with emphasis 

 on freshwater fish. Pages 49-81 in A. Rosenfield and R. 

 Mann. eds. Dispersal of living organisms into aquatic 

 ecosystems. Maryland Sea Grant. College Park. 



Sleirer, F.S.. Jr 1992. Historical perspective on exotic 

 species. Pages 1-4 in M.R. DeVoe. ed. Introductions and 

 transfers of marine species. South Carolina Sea Grant 

 Consortium. Hilton Head Island. 



Taylor. J.N.. W.R. Courtenay. Jr.. and J.A. McCann. 1984. 

 Known impacts of exotic fish in the continental United 

 States. Pages 322-373 in W.R. Courtenay. Jr.. and J.R. 

 Stauffer. Jr.. eds. Distribution, biology and management 

 of exofic fish. The Johns Hopkins University Press. 

 Baltimore. MD. 



U.S. Congress. Office of Technology Assessment. 1993. 

 Harmful non-mdigenous species in the United States. 

 U.S. Government Printing Office OTA-F-.se.';, 

 Washington. DC. 391 pp. 



Williams. J.D., and D.P. Jennings. 1991. Computerized data 

 base for exofic fish: the western United States. California 

 Fish and Game 77(21:86-93. 



400 



Before 1900 1900-1950 1950-beyon() 



Fig. 2. Diversity offish introduc- 

 tions over time. 



For further information: 



Charles Boydstun 



National Biological Service 



Southeastern Biological Science 



Center 



7920 NW 71st St. 



Gainesville. FL 326.'i3 



Interest in established, non-native species of 

 reptiles and amphibians in the United States 

 (including territories and possessions) has been 

 increasing the past quarter-century. Concerns 

 regarding the interactions of introduced and 

 native species have driven this interest (Wilson 

 and Porras 1983). Most successful introductions 

 have taken place in the southern tier of states 

 (California to Florida) and on islands. This suc- 

 cess rate is probably due. in pan. to favorable 

 environmental conditions. Movements by 

 indigenous peoples to islands also may have 

 substantially augmented existing faunas. For 

 example, in American Samoa, virtually the 

 entire terrestrial reptile fauna may have been 

 introduced by the original human colonizers 

 (T.D. Schwaner, Alabama School of Science 

 and Math, personal communication). Since 

 many species of reptiles and amphibians on 

 islands could be considered as introduced, the 

 scope of this report, for islands, is restricted to 

 those introductions that occurred after contact 

 with western societies and for the mainland 

 United States, within the past century. A review 

 of both successful and unsuccessful reptile and 

 amphibian introductions in North America is 

 presented by Smith and Kohler (1977). 



Of the documented 53 established non- 



native amphibian and reptile species (Table), at 

 least 3 — spectacled caiman iCuiniaii croco- 

 cliliis). marine toad (Biifo marimts). African 

 clawed frog (Xenopus laevis). bullfrog (Rcma 

 catesheiana). and brown tree snake (Boiga 

 irregularis) — have been established at least 30 

 years and have been sufficiently monitored to 

 enable preliminary assessment of impacts on 

 the native biota. The marine toad is established 

 in Florida, Hawaii, the Temtories of Guam, 

 U.S. Virgin Islands, and American Samoa, and 

 the Commonwealths of Puerto Rico and of the 

 Northern Mariana Islands, where it is regarded 

 as a nuisance species. The spectacled caiman is 

 established in Puerto Rico and Florida, where it 

 may be negatively affecting vertebrates. The 

 African clawed frog is established in Arizona 

 and California, but is not demonstrating any 

 apparent negative effects on native vertebrates. 

 The bullfrog is widely established in western 

 North America, Hawaii, and Puerto Rico, and is 

 implicated in restricting the range of native 

 North American ranid frogs and the Mexican 

 garter snake (Thamnophis eqiies). The brown 

 tree snake is established on Guam and is identi- 

 fied as the agent in the extirpation of native for- 

 est-dwelling birds and small reptiles. 



Non-native 

 Reptiles and 

 Amphibians 



by 



Michael James McCoid 



Caesar Kleberg 

 Wildlife Research Institute 



Marine toad (Bufo manin 



