9560

• UCREFRP Catalog Number: 9560
• Author: Valdez, R. A.
• Title: A Generalized Interactive Model to Predict Floodplain Habitat Area Needed to Recover the Endangered Razorback Sucker in the Upper Colorado River Basin - Floodplain Model Version 5.1.
• USFW Year: 2004.
• USFW - Doc Type: Logan, UT.
• Copyright Material: NO

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automated output variables. Where possible, critical variables were left as user-specified input
variables to provide user-discretion and as much flexibility to the model as possible. A
description oflife history variables used in the model is provided in Section 3.0, and the model is
described in Section 4.0. Sensitivity analyses were performed to ensure that appropriate input
variables were used and to provide a better understanding of the inter-relationships of model
variables.

2.2 Task Descriptions
Objective 1: Estimate egg production and larval emergence of razorback sucker
from spawning sites.
1bis objective was addressed by specifying the number of adult razorback sucker in the
population, the sex ratio to compute number of females, average size of females to compute
weight, number of eggs produced, and survival of eggs to hatching and larvae to emergence. The
number of adults, sex ratio, and survival of eggs and larvae are all user-specified input variables.
The output of this portion of the model is the total number of larvae' emerging from the spawning
bed(s) and available for downstream transport by river currents.
Objective 2: Estimate downstream drift of larval razorback sucker and
entrainment into floodplain habitats.
An important aspect of the survival of razorback sucker is the occurrence of floods and
availability of floodplain habitat simultaneous to the emergence and drift of larvae (Wick 1997;
Modde and Wick 1997; Muth et al. 1998; Wydoski and Wick 1998). Downstream drift rates and
entrainment of larvae into floodplain habitats is an important consideration. The proportions of
larval razorback sucker that enter floodplain habitats at varying distances downstream from
spawning sites is estimated in the model with the aid of the sub-model "Drift" that allows the
user to specify the initial number of drifting larvae (output from Objective 1), mainstem survival
rate during drift, and percentage entrainment at specified river miles. The last input variable is
provided in order for the user to simulate a particular reach of river; this aspect is illustrated in
the sample run of the model described in Section 4.0.
Drift time and distance for pelagic eggs and larvae have been simulated using artificial
eggs in smaller rivers (Dudley and Platania 1999a, 1999b). Similar approaches were used by

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