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Last modified
7/14/2009 5:02:37 PM
Creation date
5/22/2009 12:36:53 PM
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UCREFRP
UCREFRP Catalog Number
9628
Author
Gloss, S. P., J. E. Lovich and T. S. Melis.
Title
The State of the Colorado River Ecosystem in Grand Canyon - A Report of the Grand Canyon Monitoring and Research Center 1991-2004.
USFW Year
2005.
USFW - Doc Type
\
Copyright Material
NO
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<br />A '~..,~'~~\s'~~.~:;~l:.L:':f;~~:.:~. .~::.;.~(~:: '~~.:,~~;;~%~~~~i;n~~tt1!~l:'i <br />. "~.<.~ .<~""F''l" m.17i'''''~._'\,;' "'""ix 1,..~ -,~ <br />tl~~;/';"i~~f~fi::'~~~~~~ <br /> <br /> <br />)....~..~:. :., <br />,i~~.._~2=~.. ".; <br />~p~~~:.;\> <br /> <br />,-.~ <br /> <br />.:'" <br /> <br />Fishes of Grand Canyon 39 <br /> <br /> <br />Figure 4. Photomicrograph of an otolith cross-section of young-of-year rainbow trout sampled from Glen Canyon in April 2003. Otoliths <br />are minute boney structures found in the inner ear that show daily growth patterns in many fishes. The image shows the weekly striping <br />pattern (identified by white arrows and shown at magnifications of 16x (A) and 400x (Bll caused by increased growth during lower peak <br />Sunday flows (8,000 cfs) during April 2003 when normal weekday operations ranged from 7,000-13,000 cfs on a 24-h cycle (photographs <br />courtesy of Steven Campana, Bedford Institute of Oceanography, Canada). <br /> <br />the increased electro fishing catch rate and the implemen- <br />tation of Ouctuating Oows (see chapter 9, this report). <br />Otoliths (minute boney structures found in the inner <br />ear) of young rainbow trout (fig. 4) were examined in <br />2003 and 2004 to infer growth rate patterns during the <br />late spring and summer months following the end of <br />Ouctuating nonnative fish suppression flows. Microscopic <br />examination of these bony structures allows research- <br />ers to determine daily growth patterns. Results of these <br />examinations suggest that YOY rainbow trout experi- <br />enced more growth on Sundays than on other days of <br />the week in 2003; howevel~ otoliths collected in 2004 <br />do not display increased growth on Sundays. Korman <br />and others (2005) hypothesized that this difference was <br />related to less severe Oow Ouctuations on Sundays during <br />2003 as compared to 2004. <br /> <br />Mainstem Colorado River <br /> <br />Management objectives of the Glen Canyon Dam <br />Adaptive Management Program call for managing the <br /> <br />mainstem Colorado River and its tributaries below the <br />Paria River for the benefit of native fishes (GCDAMp' <br />200 I, http://www.usbr.gov/uc/rm/amp/amwg/mtgs/ <br />02jan 17/ Attach_06.pdf, accessed July 14, 2005). Fish <br />monitoring in the mainstem Colorado River is primarily <br />conducted by electrofishing or with trammel nets, hoop <br />nets, and beach seines. Each of these methods is "selec- <br />tive," or has higher efficiency for particular species or <br />fish sizes. For instance, electrofishing is very effective in <br />catching rainbow and brown trout and common carp <br />but is ineflicient in capturing adult humpback chub. <br />Alternatively, trammel and hoop nets are more eflicient <br />than electrofishing in capturing humpback chub. These <br />differences in sampling gear efficiency, coupled with <br />diflcrences in abundance, inOuence the ability of the <br />monitoring program to detect differences in abundance <br />over time and space. <br />The current monitoring program, which uses elec- <br />troEshing for rainbow trout, brown trout, and common <br />carp, is able to show trends in the abundance of these <br />species over time and space (fig. 5 a, b, c). The abun- <br />dance of rainbow trout declines as a function of distance <br />
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