9588

• UCREFRP Catalog Number: 9588
• Author: Bestgen, K. R. and e. al.
• Title: Population Status of Colorado Pikeminnow in the Green River Basin, Utah and Colorado.
• USFW Year: 2005.
• USFW - Doc Type: Fort Collins, CO.
• Copyright Material: NO

2003 period. Differences in survival rates over time may be useful to interpret trends in
population abundance.
We used Pradel's model (Pradel 1996) to estimate 1, the finite rate of population change,
which is defined as:
7X; = N; +,1N; = ?r +f,
where Nis population size at time i or i + 1, O; is survival rate, and f is the number of fish
recruited to the population at time i per adult in the population at time i. A Xj value less than one
indicated a declining population, Ii > 1 indicated an increasing population, and I; of 1 indicated a
stable population. Functionally, the Pradel model is similar to the Jolly-Seber model used to
predict survival rates but uses the capture history in reverse order to predict the probability of
entering the population (Nichols et al. 2000). A main assumption of this model is that study area
size is constant over the sampling period, which precluded the use of capture data from other
ISMP reaches in some years. Global models that fit parameters (p, S, X) for all years and river
reaches were compared with models with a reduced parameter set. The AIC, for small samples
was used as a guide in model selection. We were careful to guard against overfitting models
with the sometimes sparse data available for some reaches or rivers and focused on those that
gave reasonable estimates of parameters that were critical to understanding the status of Colorado
pikeminnow in the Green River Basin.
24
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•