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

5

I
I
I
I
I
I
I
I
I
I
I
I
;1
I
I
I
I
I
I

Bestgen et al. (1998) and Schmidt (1996) for drifting larvae Colorado pikeminnow into main
channel backwaters. The result of this sub-model provides an estimate of the proportion of
larvae produced at a spawning site that drift downstream and become entrained in floodplain
habitats at varying distances downstream from the spawning site.
Objective 3: Estimate growth and survival of larval and young razorback sucker
in floodplain habitats.
Growth and survival oflarvae, age-D, age-I, and age-2 razorback sucker is estimated in
floodplains inundated by high river flows in spring. This aspect of the model uses the output of
Objective 2 (i.e., number oflarvae entrained in floodplains) and computes numbers and sizes of
fish in the floodplain with user-specified input of number of months in the floodplain and annual ,
survival rate. The numbers of fish surviving in the floodplain is computed for low, moderate,
and high fish growth rates, in all possible combinations with low, moderate, and high fish
densities. Survival and growth rates of young razorback sucker were taken from various studies
(Modde 1996, 1997; Muth and Wick 1997; Muth et al. 1998). Additional information on
survival and growth of young razorback sucker is available from lower basin studies (Minckley
et al. 1991). Estimates of food availability were taken from various trophic energetic studies in
flooded bottomlands and main channel backwaters (Grabowski and Hiebert 1989; Mabey and
Shiozawa.1993). Using the combination oflow, moderate, and high growth rates and low,
moderate, and high fish densities, total area of floodplains is computed as acres and hectares.
Objective 4: Estimate recruitment to adults of naturally-produced razorback
sucker necessary to achieve and sustain recovery criteria.
The numbers of razorback sucker escaping from the floodplain into the mainstem at low,
moderate, and high growth rates are provided by Objective 3. The model provides total lengths
for each growth rate and computes the number of months required for the fish to reach size of
recruitment at 400 rom total length (TL). Fish may reach recruitment size in the floodplain,
depending on the number of months specified by the user. An annual mainstem survival rate is a
user-specified input variable and the numbers of razorback sucker that recruit is computed, along
with the recruitment rate. Sustainable recruitment rate is estimated at 0.30, which is equal to the
average annual mortality rate of adult razorback sucker.