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9432 (2)
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Last modified
7/14/2009 5:02:35 PM
Creation date
5/20/2009 10:09:36 AM
Metadata
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UCREFRP
UCREFRP Catalog Number
9432
Author
Modde, T. and M. Fuller.
Title
Feasibility of Channel Catfish Reduction in the Lower Yampa River.
USFW Year
2002.
USFW - Doc Type
Vernal.
Copyright Material
NO
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Base river flow volume and mean daily discharge between 31 July and 9 <br />October in 1999 were double that of 1996, 1998, and 2000. However, the <br />unseasonably high flows that occurred during this 2-1/2-month period in 1999 did <br />not appear to be responsible for the continued decline of the total number of <br />three of the most abundant non-listed native fishes (flannelmouth sucker, <br />bluehead sucker, and roundtail chub) and adult Colorado pikeminnow that were <br />collected in the fish trap during 1999. There was virtually no difference among <br />correlation coefficients for the data for the five years (1996-2000). <br />Comparisons were made for flow volume and mean daily discharge for the range of <br />flows available vs. the total aggregate numbers of three native fish. These <br />included the flannelmouth sucker, bluehead sucker, roundtail chub, and Colorado <br />pikeminnow collected in the Redlands passageway fish trap from 31 July to 9 <br />October, 1996-2000. The decline in the number of these three native fishes <br />continued in 2000 during the same period, despite flow volume and mean daily <br />discharge being about 50% lower than in 1999. <br />There was a trend that was apparent: the total number of these three native <br />fishes during the 2-1/2-month period from July through October declined steadily <br />from 1996 to 2000. The numbers of these three native fish that steadily declined <br />from 1996 to 2000 during these 2-1/2 post-runoff months could have been <br />attributed to a slow, long-term attrition or depletion of the numbers of native <br />fish in downstream river reaches as fish moved through the passageway. This <br />reduction in numbers of fish below the diversion dam could be a mark of the <br />success of the passageway. The same steady, diminishing trend also occurred for <br />12 nonnative fishes collected in the fish trap during this same period between <br />1997 and 1999. Additionally, this trend was supported by the ratio of the three <br />most abundant native fish collected in the fish trap during high passageway use <br />periods to the number collected during low use periods. This was further <br />corroborated by a weak correlation between the total number of these three native <br />fishes with water volume (low vs. medium or high water year) and the mean daily <br />discharge in each of the five years examined. <br />A possible reason that pikeminnow use of the passageway peaked in 1997 and <br />1998 was an influx of adult pikeminnow that moved upstream from the lower reach <br />to the upper reach of the Upper Colorado River in the mid-1990's. The reasons <br />for this upstream dispersal are unknown but there are several hypotheses: 1) a <br />response to seek new food sources, (i. e., sub-adult pikeminnow made upstream <br />movements due to an inadequate supply of food in the lower reach), 2) an innate <br />physiological mechanism to move upstream (e. g. , seek new home range), and 3) the <br />urge to spawn. <br />The radiotagging and subsequent monitoring of the movements of Colorado <br />pikeminnow provided no data on their use of the Redlands fish passageway. None <br />of the 33 sub-adult and adult Colorado pikeminnow implanted with radiotags during <br />1996-1999 used the Redlands passageway. Radiotelemetry did provide data on the <br />fate of some of the pikeminnow released upstream of the Redlands Diversion Dam. <br />Telemetry also. provided data on the duration that they spent upstream of the <br />diversion dam, documented when they passed over the dam, and monitored subsequent <br />movements presumed to'be related to spawning. Some radio-tagged pikeminnow were <br />located in the general vicinity with other non-radio-tagged pikeminnow during <br />spawning. And, though the opportunity existed for some of these radio-tagged <br />fish to congregate with non-radio-tagged pikeminnow believed to be spawning, <br />xiv
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