Date of this Version
Introduced, non-native trout may have detrimental competitive or predatory interactions with native fishes. However, few studies have experimentally examined interactions between introduced trout and native non-game species. Therefore, the objectives of this study were to determine 1) if non-native rainbow trout Oncorhynchus mykiss influence survival, behavior, movement, or distribution of native longnose dace Rhinichthys cataractae under laboratory conditions, 2) if non-native rainbow trout influence survival of native longnose dace under in-situ conditions using in-stream enclosures, and 3) if native fish populations or communities differ in the presence and absence of non-native trout under natural conditions.
Rainbow trout preyed on longnose dace at low rates in both laboratory and in-stream enclosure experiments suggesting that if rainbow trout and longnose dace overlap in microhabitat use, some predation is likely to occur. Therefore, it is not recommended that non-native trout be stocked in streams containing at-risk species. Size structures of longnose dace and white sucker Catostomus commersonii were larger in the presence of brown trout Salmo trutta, and size structure of longnose dace was smaller in the presence of rainbow trout under natural conditions suggesting that non-native trout presence may influence some native populations. However, creek chub Semotilus atromaculatus and fathead minnow Pimephales promelas size structures did not differ in the presence and absence of non-native trout. Greater non-native trout abundances resulted in greater distinction in native community composition and structure between sites with trout and sites without trout suggesting there may be increased risk to native communities in sites with high abundances of trout. Therefore, species-specific, as well as community-wide effects of non-native trout should be considered prior to any introductions.
Advisors: Mark A. Pegg and Kevin L. Pope