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<br />Other Factors <br /> <br />Other factors also will be monitored/evaluated through existing/planned programs to assess the health of <br />the population such as (a) expansion of the range of the endangered fish, (b) the success of efforts to <br />control nonnative fishes and the success of fish passage structures, (c) increases in usable flooded <br />bottom habitats, (d) survivallbehavior of stocked fish. Ultimately, these recovery action measures <br />should lead to an increase in the endangered fish populations. However, detecting a significant <br />population response associated with these actions could take many years. These factors will be <br />qualitatively considered in the assessment of the health of the fish population. However, consideration <br />of these factors will be secondary to the assessment of the population indices above. <br /> <br />Role of Stocked Fish <br />The presence of stocked hatchery fish can provide an inaccurate picture of the size and health of the <br />wild population. Therefore, fish stocked into the Colorado River will be marked to allow the size of the <br />wild population to be differentiated from the size of the stocked population. While stocked fish <br />contribute to the size of the adult population, the overall health of a specific population depends upon <br />successful reproduction as indicated by increased munbers of young-of-the-year fish and corresponding <br />increases in the wild adult population due to recruitment. Therefore, stocked fish will not be included in <br />the population estimates for the population status assessment. <br /> <br />Population baseline values will be established for each of the indices, including expected annual <br />variations, to reflect the current status of fish populations. Future values of these indices will be <br />compared to their population baseline values to determine if additional water depletions in the upper <br />Colorado River are biologically justifiable. The Recovery Program currently is developing recovery <br />goals for the four endangered fishes. If a population meets or exceeds the muneric goal for that <br />species, it will be considered to exhibit a positive response. However, short of reaching a specific <br />recovery goal, trends in certain population indices provide an interim assessment of a species' progress <br />toward recovery. Increases in fish populations as determined using the population indices may support <br />increasing the water depletion limits established in the biological opinion; decreases or no change in <br />populations may indicate that additional depletions are not justifiable. The Recovery Program staff will <br />develop these indices for review by the Biology Committee by April 2000. <br /> <br />Examples <br />Colorado pikeminnow from the Upper Colorado River were used in the examples described below <br />because data are readily available to establish reliable population baseline values for each of the three <br />indices: adult population size; adult length-frequency; and young-of-the-year. Similar assumptions <br />could be made for the humpback chub, as well, when sufficient data are available. <br /> <br />Individual criteria or threshold values were selected for pikeminnow adult population size and young-of- <br />year production. These indices provide an objective means by which to measure the pikeminnow <br />population response. An unambiguous negative response in either one of these indices is presumptive <br /> <br />3 <br />