Our Living Rfsmirces — Non-native Species 



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The rate of introduction of exotic species 

 increased markedly since the 1800's. as human 

 activity in the Great Lakes basin increased. 

 Almost one-third of the introductions to the 

 Great Lakes were reported in the past 30 years. 

 The first introductions of aquatic plants 

 occuned when ships discharged solid ballast in 

 the late I800"s. The opening of the St. 

 Lawrence Seaway in 1959 greatly increased the 

 number of ocean-going vessels entering the 

 Great Lakes and dramatically increased the 

 entry of exotic species by ships. Deliberate 

 releases declined after the 1800's. and entry by 

 canal increased slightly through 1959; entry by 

 railroad and highway occuixed mostly in the 

 1800"s, and unintentional releases were consis- 

 tently high since the late 1800's. 



Origins of Introduced Species 



Although most exotic species established in 

 the Great Lakes are native to Eurasia (55%) and 

 the Atlantic coast (13'7f). Great Lakes popula- 

 tions of many of these exotic species may have 

 been established from sources outside their 

 original native range. Purple loosestrife 

 {Lythmm salicario). Eurasian watermilfoil 

 (M\ii<>jih\lliim spicatum). and the Asiatic clam 

 {Corbiciila fhiininea) are examples of Eurasian 

 organisms that invaded the Great Lakes from 

 source populations established outside their 

 native ranges. Invading Atlantic coast species. 

 such as sea lamprey iPetroinyzon Diariniis) and 

 white perch [Morone americana) probably 

 entered through the Erie and Welland canals. 

 Pacific salmon (Oncorhynchiis spp.), rainbow 

 trout (O. niykiss). brown trout (Salino tnttta), 

 alewife (Alosa pseudoharengiis). and rainbow 

 smelt (Osmenis mordax) are examples of 

 species that were introduced directly into the 

 Great Lakes basin from populations in their 

 original native ranges. 



Effects of Introductions 



The ecological and economic effects of the 

 introduced fish species have been large. Of the 

 25 introduced fish species established in the 

 Great Lakes, nearly half have had substantial 

 effects. The extension of the range of the sea 

 lamprey since the 1830's contributed to the 

 decline of several fish species and severely 

 damaged the sport and commercial fisheries of 

 the Great Lakes. Millions of dollars are spent 

 annually on sea lamprey control. The lake trout 

 was the major predator species in the four 

 lower Great Lakes, and its extermination by the 

 sea lamprey allowed the alewife to move quick- 

 ly through the lakes and experience almost 

 unrestrained population growth. This growth 



was followed by massive die-offs of alewives, 

 which polluted shorelines and blocked the 

 intake pipes of water treatment plants and other 

 industries. The alewife probably also sup- 

 pressed native coregonines (Coregonus spp.). 

 yellow perch {Perca fhivescens). emerald shiner 

 {.Notropis aiheriuoides). and rainbow smelt. 

 Eventually the alewife became an important 

 prey for trout and salmon. 



The ruffe (Gymnocephahts ceruuus). a 

 small, perchlike fish, reached the St. Louis 

 River estuary in Lake Superior in ballast water 

 in the early to mid-1980's. Ruffe abundance 

 increased rapidly and in 1993, 61% (by num- 

 ber) of the fish caught in 440 bottom-trawl tows 

 in the estuary were ruffe (J.H. Selgeby, National 

 Biological Service, personal communication). 

 The ruffe is spreading to other parts of the lake 

 and has the potential to occupy at least 6.6 mil- 

 lion ha (16.3 million acres) of Great Lakes' 

 habitat that is suitable for use by native percid 

 fishes, including the economically important 

 walleye iStizostedion vitreiim) and yellow perch 

 (Edsall et al. 1993). The effect of ruffe on native 

 Great Lakes percids has not been demonstrated, 

 but yellow perch numbers in the St. Louis River 

 estuary declined markedly as ruffe abundance 

 increased. There is concern that the ruffe has the 

 potential to adversely affect percid abundance 

 in other areas of the Great Lakes. 



The common carp (Cypriiius carpio) was 

 stocked in the 1870's. but it never becaine pop- 

 ular and by the 1890's was considered a prob- 

 lem because of its negative effects on more 

 favored fish species and on waterfowl habitat. 

 The stockings of Pacific salmon and rainbow 

 and brown trout had profound and permanent 

 ecological effects on the fish fauna through 

 competition and predation. These salmonids 

 now support a major element of the fishery in 

 the Great Lakes, valued at more than $6 billion 

 annually (GLFC 1992). 



Of the fish disease pathogens introduced 

 into the Great Lakes, Gliigea liernvigi. a proto- 

 zoan, caused extensive mortality in rainbow 

 smelt in Lakes Erie and Ontario in the 1960's 



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50 



40 



S30 



20 







Introduced aaualic soecies 



Fig. 1. Inlroduced aquatic species 

 established in the Great Lakes. The 

 number of species in each category 

 is given above the bars. 



45 



Plants 

 40 -i Algae 



g Invertebrates 

 35 - Fish 



40 



Introduction method 



Fig. 2. Entry mechanisms or 

 routes of exotic species established 

 in the Great Lakes. The number of 

 species in each category is given 

 above the bars. 



The introduced ruffe 

 (Gymnocephalus cemuus). 



