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Last modified
7/14/2009 5:02:35 PM
Creation date
5/22/2009 4:53:39 PM
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UCREFRP
UCREFRP Catalog Number
9378
Author
Nesler, T. P.
Title
Recovery of the Colorado River Endangered Fishes
USFW Year
2000.
USFW - Doc Type
Biological recovery goals and criteria for Colorado pikeminnow, Humpback chub, Razorback sucker & Bonytail.
Copyright Material
NO
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<br />12 <br /> <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br /> <br />here, the minimum target population of Colorado pikeminnow ranges from 1,100- <br />1,400 adult fish for Ne=500 and a more conservative target population ranges from <br />2,300-2,700 fish as the minimum needed to maintain Ne=1 ,000. <br /> <br />It should be noted that the estimation of Ne and NJN and their application to <br />wildlife populations is a subject of debate in conservation genetic science. In <br />contrast to Franklin (1980), Nunney and Elam (1994) and Nunney (1995), Lynch <br />(1996) argues that 5,000-10,000 breeding adults each generation are necessary to <br />maintain an Ne=1,000. Frankham (1995) concluded that Ne is typically one order <br />of magnitude less than adult population sizes (NJN=0.1) when comprehensive <br />genetic estimates are used compared to demographic estimates. The author <br />states that the latter do not always include all relevant variables (i.e., fluctuation in <br />population size, variance in family size, unequal sex ratio, overlapping generations, <br />fecundity). The consequence of a very low NJN as advocated by Frankham <br />(1995) and Lynch (1996) is a greatly expanded adult population size necessary to <br />meet a desired effective population size. This has serious implications when <br />considering carrying capacity and available habitat. <br /> <br />Another consideration in determining an abundance goal for each <br />population is the amount of habitat available to support a top predator like the <br />Colorado pikeminnow. Within the three populations of Colorado pikeminnow <br />designated here, the amounts of habitat available in river miles are 223 mi in the <br />San Juan basin, 300 mi in the Colorado-Gunnison basin, and 580 mi in the Green- <br />Yampa-White basin. Using the population estimates in Appendix Table A-1, <br />annual densities of adult pikeminnow range from 2.3-5.4 fish per river mile on the <br />Yampa and White Rivers, to 5.4-7.5 on the Colorado River, to 11.4-22.2 on the <br />Green River. Average density of pikeminnow per river mile on these rivers has <br />ranged from 3.4 on the White, to 3.8 on the Yampa, to 6.7 on the Colorado, to 16.1 <br />on the Green. This suggests the ability of these rivers to support pikeminnow <br />populations are different. <br /> <br />In developing a target density and biomass of adult Colorado pikeminnow <br />populations derived from stocking, Nesler (1998) established a density of 10 adult <br />fish/mi based on determinations that the pikeminnow biomass would be 11 % of the <br />available prey fish base biomass and 1 % of the total fish community biomass. It. <br />was recognized that the river reaches designated to support these populations <br />were at the upper elevation of historic range and the criteria used to target this <br />density was experimental and subject to change based on monitoring data. As <br />stated in the stocking plan (Nesler 1998), it would remain to be demonstrated if the <br />populations restored by stocking in the upper river segments could be maintained <br />naturally at 10 fish/mi. Given the population objectives for this stocking effort, the <br />target population abundance in the Colorado-Gunnison basin (based on a wild <br />population in the Grand Valley portion of the Colorado River and two restored adult <br />populations in the upper Colorado and Gunnison) would be approximately 1,650- <br />2,000 adult fish. This range is based on average population size derived from <br />
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