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A. FLOWING RIVERS 1. Status of rivers: Native fishes remain a component of the fish community in flowing river reaches within Glen Canyon NRA. Nonnative fish do not thrive in harsh spring flood conditions. These are the very conditions that have been controlled by water development upstream from the Glen Canyon NRA. Although surveys of the river reaches within the NRA are incomplete, native fishes numbers are low and the listing of four endemic species as endangered illustrates the severity and urgency of the problem. The four endangered fishes are generally considered long-lived species, and some are known to migrate great distances to spawn. Larvae of these species also drift long distances in river current until they settle in backwaters or slackwater nursery habitats. Biocontaminants have potential detrimental impacts to .fisheries. Naturally occurring trace elements, and trace elements from irrigation return flows, enter the food chain in plankton then bioaccumulate within organisms and biomagnify up the food chain. Long-lived species and top predators tend to concentrate some elements to levels that could negatively affect survival or reproduction. Causes for decline of native fish in the rivers are not fully understood, but could include loss and change of habitat, competition/predation from nonnative species, and biocontaminants. Many nonnative species have been intentionally introduced into impoundments and have found their way into the river reaches. The most troublesome species were not intentionally introduced into the river but have invaded from other sources. Invading channel catfish, northern pike, striped bass (seasonal runs), red shiner, and common carp exacerbate the recovery effort in the river reaches. Researchers indicate that nonnative species dominate catches in the rivers with red shiner being the most numerous species. Adult forms of these species may prey on native fish while the juvenile and larval stages compete for limited food and habitats. The Colorado River supports more native fish species and numbers than the other tributaries into Lake Powell. Regulated river flows minimize natural extremes in flow which allows nonnative fish to occupy habitats which otherwise would not be suitable for them. 2. Goal for Rivers: To protect, restore and recover, where possible, native fish populations, particularly threatened and endangered fishes endemic to the Colorado River Basin, within Glen Canyon NRA. 3. Flowing River Management Objectives a. Understand native fish habitat requirements and-life history. b. Ensure that optimum instream flow regimes required for native fish recovery are maintained. c. Conserve native fish populations while maintaining genetic integrity. 16