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<br />EXECUTIVE SUMMARY <br />The purpose of this document is to outline quantifiable interim management objectives (IMOs) for <br />all Colorado River endangered fish and describe how they were developed. The term "interim" is <br />being used because they will require refinement at regular intervals as new information is <br />obtained. The application of IMOs will be primarily within the UBRIP to evaluate progress <br />towards recovery of these endangered fish. In this light, the IMOs will provide a framework for <br />prioritizing short-term actions needed for recovery and guidelines for obtaining the information <br />needed to define quantifiable long-term recovery objectives. <br />These IMO's were quantified in terms of viable population size estimates. They represent the <br />number of individuals in a population (N.) that the Upper Basin Recovery Implementation <br />Program (UBRIP) should target to achieve through recovery management actions. These <br />estimates incorporate two basic biological components: maintenance of genetic variability <br />(expressed as NJ and population demographic stability (incorporated within N.). The process <br />used to develop the IMOs was based upon a review of a number of methods for quantifying <br />population status, minimum viable population size, listing criteria, and conservation criteria. This <br />approach incorporated: 1) the conceptual technique for developing de-listing criteria for sea otter <br />outlined in Ralls et al. (1996), 2) the application of empirical information for measuring effective <br />population sizes for Pacific salmon stocks as suggested by Waples (I990a,b and 1991), 3) the <br />methods for calculating populations parameters important for prioritizing recovery efforts by <br />Allendorf et al. (1997), and 4) the methods for establishing listing criteria by Mace and Lande <br />(1990). The acceptable level of risk for long-term viability was set at a 95% (19 in 20) chance of <br />persistence for 100 years. <br />The following process was adhered to for each species and their representative sub-populations in <br />the UCRB. First, the number of populations or sub-populations was identified. Second, a <br />minimum effective population size (J was set as a constant for all populations. Third, sex ratio <br />was estimated based on empirical evidence and varied from species to species. Fourth, the <br />number of individuals breeding in the population (Nb) required to maintain N. was estimated based <br />on sex ratio. Fifth, the ratio of effective population size to census population size (N)N) was set <br />as a constant for all populations. Sixth, the number of individuals in the population required to <br />maintain the genetic diversity (Ng : based on Nb and N." was estimated. The seventh and final <br />calculation involved accounting for the population demographic features by using Crowl and <br />Bouwes (1998) life stage models. <br />Calculated IMO values for each species included: 5477 (±966) for Colorado squawfish, 5316 <br />(±804) for razorback sucker, 4796 (±1317) for humpback chub, and 4118 (±817) for bonytail. <br />These values represent the total number of adults (Nm) required to reach a 95% probability of <br />maintaining Ng adults for at least 100 years. A discussion of how they can be used in combination <br />with life-stage models for prioritizing management actions is included. Monitoring population <br />responses in relation to these IMOs is also discussed. Recommendations for application of IMOs <br /> <br />v <br />1