Lect16MtnLakesBackground-1

Lect16MtnLakesBackground-1 - The introduction of salmonid...

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Unformatted text preview: The introduction of salmonid fishes into mountain lakes of the Sierra Nevada of California is an ideal case study to explore the potential value of simple, structural food webs for visualizing and communicat- ing about the community-level impacts of an introduced species. More than 99% of the approximately 10,000 high elevation lakes (I:- 3000 ml in this approximately 5 million hectare range were historically fishless as a result of numerous barriers to upstream movement by fishes [Bahls, 1992; Knapp, 1996]. Fish stocking began in the mid-18005 to provide recreational fishing opportunities, and over the course of the next century trout were introduced into 80%—95% of the lakes (Bahls, 1992: Knapp, 1996; Knapp and Matthews, 2000: Schindler et al., 2001]. The most commonly introduced species were rainbow trout (Oncorhynchus mykiss}, golden trout (O. m. oguabonita}, and brook trout (Salvelimts fontimrlis). Trout are voracious generalist predators and, as in other aquatic sys- tems throughout western North America, they have had a dramatic impact on the aquatic fauna. Many of these impacts appear to be 7.5 | a Case Study 409 directly trophically mediated Wander Zanden et al., 2000; Knapp et at, 2001; Beisner et al., 2003; Vander Zanden et al., 2003]. Recently, the improved understanding of the impacts of fish introductions on Sierra Nevada lake ecosystems has resulted in increased scrutiny of fish stock- ing practices. However, in the development of new stocking manage- ment strategies, community-level impacts of trout have generally been ignored and all focus has been directed at a single ‘charismatic’ Species, the mountain yellow-legged frog [Rene museum} whose distribution and abundance is strongly influenced by introduced fish (Bradford, 1989; Knapp and Matthews, 2000; Knapp et al., 2001;Vredenburg, 2004). As a consequence of strong predation by trout on R. muscosa tadpoles and adults, this species is now extirpated from 50%—80% of its historic localities (Bradford et 21]., 1994: Drost and Fellers, 1996; Jennings, 1996}. Consequently, the US. Fish and Wildlife Service recently determined that the listing of R. muscosa as “endangered” under the US. Endangered Species Act is warranted (Federai Register, 2003]. Due to the increasingly precarious status of R. muscosa, the California Department of Fish and Game recently halted most stocking of non-native trout in high elevation Sierra Nevada lakes and efforts to restore some lakes to their naturally fishless condition are underway {Knapp and Matthews, 1998; Milliron, 1999; Vredenburg, 2004}. This single-species focus was likely due, in part, to the ease of describing the fish-frog interaction compared to the considerably more complicated community-level changes that accompany fish introductions. ...
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