9443

• UCREFRP Catalog Number: 9443
• Author: Bestgen, K. R., G. B. Haines, R. Brunson, T. Chart, M. Trammell, R. T. Muth, G. Birchell, K. Chrisopherson and J. M. Bundy.
• Title: Status of Wild Razorback Sucker in the Green River Basin, Utah and Colorado, Determined From Basinwide Monitoring and Other Sampling Programs.
• USFW Year: 2002.
• USFW - Doc Type: Project Number 22D,
• Copyright Material: NO

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for all time periods (~ = 0.72, 1980 to 1992; ~ = 0.76, 1990 to 1999) and were consistent with
the early estimate from Modde et al. (~ = 0.71, SE = 0.0246). Small differences in 1980 to 1992
estimates from Modde et al. (1996) and this study were likely due to recent changes in capture
histories of some individuals that were used in each analysis.
The cp parameter in the Pradel model was also consistent with other estimates of survival
of razorback suckers in the middle Green River. Pradel's ~,, which estimates annual population
rate of change from all sources including emigration, immigration, mortality, and recruitment,
also suggested that the razorback sucker population was declining over time. However, the ~,
parameter appears sensitive to large differences in sample sizes that occurred in the early 1980's
and data is likely too sparse for reliable parameter estimation. Thus, we do not place much
confidence in ~, estimates and instead rely on estimates of survival and population abundance to
make inferences about the status of wild razorback suckers in the middle Green River.
If one assumes that 500 razorback suckers remained in 1992, average annual survival rate
between the six yearly intervals until 1999 was 0.76 (our 1990 to 1999 estimate), and no
recruitment or tag loss occurred over the period from 1992 to 1999, about 73 fish should remain
(Fig. 10). This estimate is consistent with the average estimated abundance of 116 for the 1998-
1999 period. This again suggests that little or no recruitment occurred from 1992 to 1999.
Larvae, middle and lower Green River.- Reproduction by razorback suckers was
documented from 1996 to 1999 in both the middle and lower Green River reaches based on
captures of early life stages of razorback suckers in each reach. That data extends the record
documenting annual reproduction in the middle Green to 10 years (since 1992, Muth et al. 1998)
if 2000 and 2001 are considered (unpublished data, K. Bestgen, Larval Fish Laboratory, Colorado
State University). Reproduction occurred in seven consecutive years in the lower Green River
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