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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
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<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 />maintain a desired Ne (Lentsch et al. 1998). This factor for genetic contribution to <br />the next generation, NJN, has been estimated for only a few fish species or <br />genera (see Lentsch et al. 1998; Frankham 1995). None of the taxa have a life <br />history-longevity combination similar to those established for Colorado pikeminnow <br />or the other endangered Colorado River fish species. Nunney and Elam (1994) <br />and Nunney (1995) suggested that a good approximation of NJN is 0.5 for a <br />variety of mating systems. The authors indicate that as adult longevity and <br />generation time increases, Ne tends to equal N/2 regardless of the mating system <br />employed. As described in Nunney and Elam (1994), the Colorado pikeminnow <br />breeding strategy appears most similar to a random union of gametes from <br />overlapping generations within several, independently regulated subpopulations. <br />Nunney and Elam (1994) indicate this subdivision increases effective population <br />size, even though the subpopulations may become genetically homogenous. <br />Variation in lifetime reproductive success is largely due to the mating system and <br />longevity (Lentsch et al. 1998). As described in Nesler (1998) concerning the <br />contribution of adult fish to succeeding generations, adult Colorado pikeminnow <br />are late-maturing, long-lived, and highly fecund. All of these attributes enhance <br />the potential for any individual adult fish to contribute to succeeding generations <br />over at least 10-20 years of reproductive activity during an adult fish's lifetime. <br />Osmundson et al. (1996) demonstrated the potential for adult Colorado <br />pikeminnow existing for 20-50 years. <br /> <br />Biased sex ratios (male:female, M:F) during spawning, a common trait in <br />many fish species, and presumably in the endangered fishes as well, also affect <br />and increase the population abundance necessary to maintain Ne. Given these <br />considerations, the target abundance of a genetically viable population may be <br />estimated using formulae provided in Wright (1931), Frankham (1995) and Lentsch <br />et al. (1998). <br /> <br />Assuming a sex ratio of 3M: 1 F and an NJN=0.5 for Colorado pikeminnow <br />the target abundance is estimated at approximately 2,700 adult fish in order to <br />maintain an Ne=1,OOO. If a sex ratio of 2M:1F is used, the target abundance <br />necessary to maintain Ne is reduced to approximately 2,300 fish. Given these <br />factors and a population survival rate of 0.86, an NJN value of 50% may be <br />conservative. Repeating these calculations using Ne=500, the target abundance . <br />necessary to maintain this lower Ne ranges from 1,100-1400 fish. <br /> <br />The size of a population needed to maintain an effective population size and <br />genetic diversity is affected by NJN and M: F. In the case of the Colorado <br />pikeminnow and the other endangered Colorado River fishes, neither has been <br />estimated with any reliability. The size of spawning adult populations relative to <br />total population and the sex ratio during egg deposition and fertilization have not <br />been studied. Miller and Ptacek (2000) observed three Colorado pikeminnow <br />engaged in apparent spawning behavior in the San Juan River, and made a visual <br />observation of radiotagged male and female Colorado pikeminnow in presumed <br />spawning activity paired 1 M: 1 F. Using a feasible array of M: F and NJN values <br /> <br />11 <br />
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