8055 ‎(2)‎

• UCREFRP Catalog Number: 8055
• Author: Crowl, T. A. and N. W. Bouwes.
• Title: A Population Model for Four Endangered Colorado River Fishes - Final Report.
• USFW Year: 1998.
• USFW - Doc Type: Logan, Utah.
• Copyright Material: NO

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downstream, a proportion die based upon the juvenile mortality rate for dispersal. The
further a juvenile has to move downstream, the less likely it is to survive. Currently, the
model is set for 10% mortality for fish <2 yrs old.
4. At-the end of each time step (1 yr), the number of survivors in each age category
become one year older, except for adults, the terminal age class. The age-specific
survivorship rates for each year are randomly generated based upon empirically
derived estimates + randomly generated standard, lognormal deviates. The standard,
lognormal deviate depends upon the observed standard deviation for each age-specific
mortality rate.
5. The processes of 1- 4 are repeated for the next year, etc.
By generating the population dynamics for 100 years for 100 replicated populations,
the percentage of populations that fall below the hypothesized extinction threshold
(minimum number of individuals) or any management-derived target values denotes the
likelihood that the population will persist for 100 years.
Final Model Description
Because the Mathcad modeling software is not widely used, we rewrote the original
model using the Quattro Pro (Version 7 for Windows 95 using PC computers) platform.
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