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coldwater fishes can move downstream into habitats occupied by native fishes and <br />predation at that time may be high. <br />Cold water released from Glen Canyon Dam in the Colorado River supports a <br />substantial tailwater trout fishery in Grand Canyon. Trout predation on native warmwater <br />cyprinids that enter mainstream waters from warm tributaries has been well documented <br />(Marsh and Douglas 1997). Valdez and Ryel (1995) estimated that brown trout <br />consumed 230,000 humpback chub annually in the Grand Canyon, and that rainbow <br />trout consumed 27,375 annually. These authors also reported evidence of competition. <br />The yellowfin cutthroat trout (Oncorhynchus clarki macdonaldi) of the east slope <br />of the Rocky Mountains was one of the earliest cases of a native trout driven to <br />extinction. Native to the upper Arkansas drainage its last populations were reported in <br />Twin Lakes, Colorado, where they were abundant in the 1870's. However, their <br />extinction was attributed to overfishing and introduction of rainbow trout, brook trout, lake <br />trout, and Atlantic salmon (Salmo salary in 1890. By 1903, the rainbow trout were <br />dominant, and no yellowfin trout were found then or later (Ellis 1914, USFWS 1998). <br />The major factor in the decline of the greenback cutthroat trout in the South Platte <br />and Arkansas drainages in Colorado was the introduction of non - native salmonids: <br />rainbow, brook, brown, and Yellowstone cutthroat trouts. The greenback trout hybridizes <br />with rainbow trout and other subspecies of cutthroat trouts, it is displaced by brook trout, <br />and prey to rainbow and brown trouts ( USFWS 1998). <br />An exhaustive accounting of the adverse interactions between various species of <br />salmonids is presented by Fuller et al. 1999. These accounts leave little doubt that <br />introduced salmon, trout, and other salmonid fishes can and do compete with, prey <br />upon, and hybridize with native salmonids, and compete with and prey upon many other <br />species as well. <br />— Coolwater introductions <br />Coolwater lakes are transitional between coldwater and warmwater systems. <br />Coolwater lakes are characterized by predatory fishes such as northern pike, <br />muskellunge, walleye, yellow perch and smallmouth bass. These species also can thrive <br />in both cold and warmwater habitats, which they tend to move into depending on <br />season. <br />Northern pike and walleye are avidly sought by recreational fishing interests, thus <br />these species are the most popular coowater fishes for introductions. However, <br />stockings of these species have met with controversial results due to reduction of prey <br />species, piscivory on salmonids, and invasions into adjoi ni ng. watersheds, and there is <br />concern about risks associated with additional introductions (McMahon and -Bennett <br />1996). <br />16 <br />