Laserfiche WebLink
stocked juveniles. Through augmentation, Colorado pikeminnow are generally distributed <br /> throughout the San Juan River within critical habitat. <br /> 2.1.4 Threats <br /> The Colorado pikeminnow was designated as an endangered species prior to enactment of the <br /> ESA, and therefore a formal listing package identifying threats was not assembled. Construction <br /> and operation of mainstem dams,nonnative fish species, and local eradication of native minnows <br /> and suckers in advance of new human-made reservoirs in the early 1960's were recognized as <br /> early threats (Service 2002a). According to the 2002 Recovery Goals for the species,the <br /> primary threats to Colorado pikeminnow populations are streamflow regulation and habitat <br /> modification (including cold-water dam releases,habitat loss, and blockage of migration <br /> corridors); competition with and predation by nonnative fish species; and pesticides and <br /> pollutants (Service 2002a). <br /> In the Upper Basin, 435 miles of Colorado pikeminnow habitat has been lost by reservoir <br /> inundation from Flaming Forge Reservoir on the Green River, Lake Powell on the Colorado <br /> River, and Navajo Reservoir on the San Juan River. Cold water releases from these dams have <br /> eliminated suitable habitat for native fishes, including Colorado pikeminnow, from river reaches <br /> downstream for approximately 50 miles below Flaming Gorge Dam and Navajo Dam. In <br /> addition to main stem dams, many dams and water diversion structures occur in and upstream <br /> from critical habitat that reduce flows and alter flow patterns,which adversely affect critical <br /> habitat. Diversion structures in critical habitat can divert fish into canals and pipes where the <br /> fish become permanently lost to the river system. It is unknown how many endangered fish are <br /> lost in irrigation systems,but in some years, in some river reaches,the majority of the river flow <br /> is diverted into unscreened canals. Peak spring flows in the Green River at Jensen, Utah,have <br /> decreased 13-35 percent and base flows have increased 10-140 percent due to regulation by <br /> Flaming Gorge Dam (Muth et al. 2000). <br /> Although a good portion of the recovery factor criteria(Service 2002a) are being addressed, <br /> nonnative fish species continue to be very problematic. Recovery Goals (Service 2002a, 2002b, <br /> 2002c, 2002d) identified predation or competition by nonnative fish species as a primary threat <br /> to the continued existence or the reestablishment of self-sustaining populations of Colorado <br /> pikeminnow and the other three endangered fishes (Martinez et al. 2014). Predation and <br /> competition from nonnative fishes have been clearly implicated in the population reductions or <br /> elimination of native fishes in the Colorado River Basin (Dill 1944, Osmundson and Kaeding <br /> 1989, Behnke 1980, Joseph et al. 1977, Lanigan and Berry 1979, Minckley and Deacon 1968, <br /> Meffe 1985, Propst and Bestgen 1991, Rinne 1991). Data collected by Osmundson and Kaeding <br /> (1991) indicated that during low water years nonnative minnows capable of preying on or <br /> competing with larval endangered fishes greatly increased in numbers. The Colorado River <br /> Basin is an altered riverscape and the interaction of native and nonnative species with <br /> non-adapted and competing life histories has contributed to what may be the largest expansion of <br /> nonnative fishes and displacement of native fishes in a North America river basin (Martinez et al. <br /> 2014). More than 50 nonnative fish species were intentionally introduced in the Colorado River <br /> Basin prior to 1980 for sportfishing, forage fish,biological control and ornamental purposes <br /> 14 <br />