Laserfiche WebLink
<br />002J98 <br /> <br />16 <br /> <br />Non-native Fish: <br />The number of common non-native fish species in Grand Canyon remains relatively <br />low Although potentially reduced from pre-dam levels. carp remain a relatively abundant <br />non-native species. with large numbers seen year-around in the lower LCR and commonly <br />throughout the mainstream. Carp have been present in the river since the late 1880's, but no <br />pre-dam population data are available for Grand Canyon, and the effects of carp on native <br />species remain undocumented. Channel catfish aggregate annually in spring and early summer <br />in the LCR for presumed spawning. This species is a documented predator of humpback <br />chub, and may be the subject ofa control program in 1998. Fathead minnows are abundant in <br />mainstream backwaters, and population increases may be attributable to more stable <br />mainstream flows. Although densities may be temporarily decreased by high flows. many <br />tributaries in Grand Canyon harbor populations for reinvasion into the mainstream Red <br />shiners were relatively abundant in the LCR during 1996, perhaps because the LCR did not <br />experience a spring flood, are becoming more common in the mainstream downstream, and <br />are very abundant in the lowermost Grand Canyon. Other non-native species such as black <br />bullhead (Ameiurus melas), green sunfish (Lepomis cyanellus), largemouth bass (Micropterus <br />salmoides), and plains killifish (Fundulus zebrimus) continue to be uncommon in the <br />mainstem. <br /> <br />Trout: The blue-ribbon rainbow trout fishery from the dam to Lees Ferry is currently <br />primarily sustained by natural reproduction: 70 percent of the rainbow trout in the tail water <br />are naturally produced, while 10 years ago, most fish were of hatchery origin. Although large <br />trout in excess of 5 pounds were numerous before 1983, these large fish are now rare (Figure <br />5). Nevertheless, a large population of trout is currently being sustained by the high biomass <br />of amp hip ods (Gammarus lacustris), midges (Chironomidae) and blacktlies (Simuliidae) in the <br />Glen Canyon reach. The condition of trout in this population has improved since the <br />implementation ofInterim Flows in 1991, and further in 1995-1996; however. trout condition <br />remains a concern (Figure 6). Further downstream, resident populations of rainbow trout <br />persist throughout Marble and Grand Canyon, and spawn in and around tributaries. such as <br />Nankoweap Creek, Bright Angel Creek, Shinumo Creek. Deer Creek, and Tapeats Creek. <br />The trout population in and around Bright Angel Creek has become increasingly dominated by <br />brown trout (Salmo trutta) in the last 15 years (Valdez and Rye1 1995). <br /> <br />Native Fish: <br />Remaining native fish populations are variously dispersed through Grand Canyon. but <br />all four species seem to be experiencing difficulties with reproductive success and recruitment. <br />Mainstream water temperatures of 80C to 160C continue to be below optimum ranges ( 16- <br />220C) for reproduction and survival of eggs and larvae of these warm water species. <br /> <br />Final Draft - 12/12/97 - For AMWG Review <br />