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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 />produce 1,740 age-3 fish in a single year is about 3,068 acres. Model runs also indicate that <br />estimated floodplain area necessary to support a population of 10,000 adult razorback sucker <br />ranges from 133 to 5,289 acres, given the same model assumptions. The model also estimated <br />that the 6,000 acres of potential floodplains at average peak: flows of the Green River could <br />support a population of about 11,350 adults, given the conditions of the model and the <br />appropriate timing, availability, and suitability of the floodplain habitat. <br />Model Sensitivity <br />Parameters (i.e., input variables) that determine floodplain area necessary to support a <br />given population size of razorback sucker are largely unknown, and use of these parameters gives <br />the model output varying degrees of uncertainty. However, a reasonable range of values for <br />some parameters is known and can be used as a starting point to gauge the value of other lesser <br />known parameters. This allows the user to "game" with the model in trying to better understand <br />unknown variables and inter-relationships. Initially, the model may have limited utility, but as <br />more is known about conservation of the razorback sucker and the population expands, there will <br />be more opportunity to ground-truth and refine the model. The area of floodplain habitat <br />necessary can be more precisely assessed as empirical data are collected from ongoing <br />investigations that provide greater accuracy for model inputs. Empirical data needed for this <br />model refinement include estimates of longitudinal survival/and retention of drifting larvae, <br />percent entrainment of larvae into floodplains, and monthly survival offish in floodplains and in <br />the main river channel. I recommend that the Recovery Program maintain and refme this model <br />as a tool in helping to understand those aspects of the Habitat Restoration Program that are most <br />critical to the recovery of the razorback sucker. <br />Use of floodplains by razorback sucker depends on many factors external to species <br />demography, including timing of availability, duration of connection with the mainstem, and <br />ability of the floodplain to hold quality water for overwintering fish. It is also unknown if the <br />inter-annual frequency of flooding is sufficient to establish and maintain a demographically and <br />genetically viable population of razorback sucker. A recruitment model that simulates survival <br />for the historic hydrographic record of the Green River may be necessary to provide insights into <br />inter-annual flood frequency necessary to maintain a population of 5,800 adults. <br /> <br />Vll <br />