Our Liviiii^ RcM'urci's — Fishes 



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The indigenous fishery of Glacier Natiitnal 

 Park has been radically altered IVoni its pris- 

 tine condition during the past half-century 

 through introductions of non-native fishes and 

 the entry of non-native species from waters out- 

 side the park. These introductions ha\e adverse- 

 ly affected the native westslope cutthroat trout 

 (Oncorhyiuhus clarki Icwisi: Fig. I ) throughout 

 much of its park range. 



The effects of non-native fishes on indige- 

 nous fisheries have been reviewed by Taylor et 

 al. (1984), Mamell (1986), and Moyle et al. 

 (1986). Effects of fish introductions in Glacier 

 National Park include establishment of non- 

 native trout populations in historically fishless 

 waters, genetic contamination (i.e.. hybridiza- 

 tion) of some native westslope cutthroat trout 

 stocks, and ecological interferences with vari- 

 ous life-history stages of native trout. 



Research conducted in the park during the 

 1980's addressed the genetic effects of fish 

 introductions on native trout. Of 47 lakes 

 known or suspected to contain cutthroat trout or 

 trout hybrids. 32 lakes contained viable popula- 

 tions of cutthroat trout, rainbow trout ^0. 

 inykiss). or hybrids. Trout introduced in the 

 other waters were evidently unable to sustain 

 themselves through natural reproduction. 



Fig. 1. Westslope cutlhroat trout {Oiuiirlixncluis chirki 

 Icwisi). 



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t^tsu^" 



mt- 



^Wk/- 



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Fig. 2. Yellowstone cutthroat trout (Oncorhynclnis ciarki 

 boKvifii). 



About 30 trout sampled from each lake 

 underwent laboratory genedc analyses. Close 

 agreement of the results from two analytical 

 procedures yielded a high degree of confidence 

 in the conclusions (Mamell et al. 1987). Genetic 

 classifications in Tables 1 and 2 reflect the com- 

 bined results of the analyses. 



Fourteen pure strain populations of west- 

 slope cutthroat trout persist in 15 lakes (i.e., 

 some interconnected lakes contain a single trout 

 population) in the North and Middle Fork 

 drainages of the Flathead River; the species was 

 historically present in these waters (labeled as 

 "stable" populations in Table 1 ). 



Pure strain native trout also inhabit four 



other Middle Fork lakes (i.e.. Avalanche, 

 Snyder, and Upper and Lower Howe lakes), but 

 it is unclear whether they are indigenous or 

 were transplanted from other park waters. 

 Recent findings from sediment paleolimnology 

 studies suggest that trout have been present in at 

 least one of these lakes for more than 300 years 

 (D. Verschuren. University of Minnesota, and 

 author, unpublished data). Hence, trout popula- 

 tions in these four lakes are tentatively classi- 

 fied as indigenous (Table 1 ). 



Introduced populations of Yellowstone cut- 

 throat trout {O. clarki boiivieri; Fig. 2) and trout 

 hybrids including cutthroat-rainbow trout [0. 

 clarki spp. x O. inykiss) occur in 13 lakes dis- 

 tributed anions the three continental drainages 



■ WCT — pure strain westslope cutthroat trout 

 YCT — the introduced Yellowstone cutthroat trout 

 X — two or more species have hybridized 



"Stable — native population exists in a pristine environment 

 Unstable — declining condition resulting from presence ol competing 

 non-native species- 



Hybrid and non-native populations — classified without regard to popu- 

 lation condition 



•YCT— introduced Yellowstone cutthroat trout 

 X — two or more species have hybndized, 

 RBT— rainbow trout 

 WCT — westslope cutthroat trout. 



"Hybrid and non-native populations are classified without regard to popu- 

 lation condition. 



Cutthroat 

 Trout in 

 Glacier 

 National Park, 

 Montana 



by 



Leo F. Mamell 



National Biological Service 



Table 1. Status and trends of cut- 

 throat trout and their hybrids in the 

 North and Middle Fork. Flathead 

 River drainages of Glacier 

 National Park. Montana. 



Tabic 2. Status and trends of non- 

 native and hybrid trout populations 

 in the South Saskatchewan and 

 Missouri ri\er drainages of Glacier 

 National Park. Montana. 



