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Last modified
7/14/2009 5:02:36 PM
Creation date
5/20/2009 10:07:40 AM
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UCREFRP
UCREFRP Catalog Number
9499
Author
Osmundson, D. B.
Title
Removal of Non-native Centrarchids from Upper Colorado River Backwaters, 1999-2001
USFW Year
2003.
USFW - Doc Type
Summary of Results.
Copyright Material
NO
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Control efforts in an individual backwater <br />In the Horsethief backwater, total catch of green sunfish per seasonal effort <br />displayed a general downward trend over the three years (r2 = 0.67; P = 0.02), but no <br />reductions were evident during the last three seasonal efforts while the backwater <br />remained isolated (r2 = 0.0; P = 0.96). For largemouth bass, just the opposite was <br />observed: no overall reduction was evident during the six efforts (r2 = 0.1; P = 0.53); in <br />fact, total catch in fall 2000 increased 5-15 times that of the previous three efforts (Fig. <br />6). However, total catch did decline during the last three seasonal efforts when the <br />backwater remained isolated (Y-2= 0.97; P = 0.08). <br />Length frequencies of green sunfish and largemouth bass indicated fairly stable <br />size structures of both populations during the one-year period when Horsethief <br />backwater was isolated (Figs. 7). As expected, there was very little change in length <br />frequency of both species between fall (October 3) 2000 and spring (April 11) 2001 <br />when low winter temperatures would likely have reduced growth rates. However, there <br />was a noticeable shift to higher frequencies of larger fish by late summer (August 28) <br />1000 <br />800 <br />a? <br />L <br />600 <br />U <br />L <br />400 <br />E <br />Z <br />200 <br />0 <br />Horsethief backwater <br />------------------------------------------------- <br />------------------------------------------------- <br />--------®-------------------------------- <br />®Green sunfish <br />El Largemouth bass <br />----_--------------------- <br />sp-99 fa-99 sp-00 fa-00 sp-01 <br />Removal efforts <br />fa-01 <br />Figure 6. Total number of largemouth bass and green sunfish captured from Horsethief <br />Backwater (rm. 154.5) with barge electrofishing on each of six occasions, 1999-2001. <br />14
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