Influence of Trout Stocking on Tier I/II Fishes
The Nebraska Game and Parks Commission (NGPC) continually receives political pressure to stock native and non-native fish throughout the state. In many instances, stocking fish enhances recreational opportunities for anglers. However, in some instances, stocking fish mars the integrity and stability of biotic communities.
Currently, the NGPC discourages stocking trout in streams that are home to tier I/II fishes because of concern for these fish communities. Tier I/II fishes, or species of concern, are species for which conservation actions are considered vital for survival. Specifically, there is concern that introduced trout will consume, or compete with, tier I/II individuals. Thus, introduced trout could potentially harm tier I/II fishes
GoalsThe goal of this project was to gain a better understanding of the interactions between non-native trout and species of concern in Nebraska headwater streams to better predict the outcomes of future trout stockings. Specific objectives of this project were to determine 1) if non-native rainbow trout influence survival, behavior, movement, or distribution of native longnose dace 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.
This project is complete. 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. Size structures of longnose dace and white sucker were larger in the presence of brown trout, 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 and fathead minnow 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 fish-community composition and structure between sites with and without trout suggesting there may be increased risk to native communities in sites with high abundances of trout. Therefore, species-specific and community-wide effects of non-native trout should be considered prior to introductions.