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The other potential effects to native fish from nonnative species are more difficult to quantify. Harassment of native species by nonnative fish can include nonpredatory attacks that disrupt sheltering. breeding or feeding behavior or the elimination of habitat features (e.g. aquatic vegetation) utilized by the native species. These types of actions make it more difficult for the native fish to successfully utilize a specific habitat, thus contributing to declines in or the local extinction of the population. The role of nonnative fish introductions in the spread of new diseases and parasites in the Basin has not been fully evaluated. The spread of the parasite Lernea sp. in the Basin is very likely the result of nonnative introductions. The continued stocking of nonnative fish, even those already established in the Basin, adversely affects the native fish species. The stocking may enable a species to maintain a higher population level than the habitat could support, increasing the effectiveness of competition against the native species. In cases where natural events such as drought or floods have reduced nonnative fish populations, stocking allows them to regain pre-event population levels faster than would occur naturally. This may suppress native fish recovery in the area. However, it should be noted that at present, very little warmwater stocking occurs in Utah and Wyoming. A. No Action Alternative 1. Aquatic Biological Resources: Although Utah and Wyoming have no current plans for stocking warmwater fishes in the Upper Basin, with no stocking procedures in place future stockings could occur. As such stockings occur, nonnative fish occurrence in the river would increase. Additionally, determinations could be made to introduce new species into the basin. In the recent past, Utah has considered impacts to the endangered fishes even though no stocking procedures have been in place. Utah considered stocking rainbow smelt into Lake Powell to improve recreational fishing, but through a review process, tabled their proposal because of concerns on the downstream humpback chub population. In the past, Wyoming has stocked channel catfish into the Little Snake River. They stopped stocking in 1990, when a Colorado squawfish was captured in the Wyoming portion of the Little Snake River. However, with no formal procedures in place, resuming stocking would be totally at their discretion. Stocking in Colorado by the aquaculture industry into private ponds for approved species would continue and likely increase. Chronic escapement from ponds with outlets to the river and when the floodplain became inundated would continue and probably increase. The occurrence of channel catfish, largemouth bass, bluegill, black crappie, fathead minnows, green sunfish, etc. in the river would therefore increase. Competition with and predation on the endangered fish would increase. Stocking by the Colorado Division of Wildlife would continue in public waters. Colorado would continue to try and increase warmwater fishing opportunities in western Colorado, while trying to minimize impacts to the endangered fishes. Stocking into private ponds would likely occur 27