K. R. Bestgen, K. A. Zelasko, and G. C. White. Monitoring ...

Low precision of survival rate estimates reflected the low probabilities of capture of fish
in each reach, but particularly for the middle Green River, where capture rates ranged from
0.004–0.02 over the three-year period (Table 7). Capture rates for the lower Green River were
slightly higher and more fish existed in that reach, so p’s were slightly higher at 0.01–0.07 over
the 2006–2008 period. Those rates consisted of the following across-year captures: 2 fish
captured in 2006 and 2007, 9 fish captured in 2006 and 2008, 11 fish captured in 2007 and 2008,
and 1 fish captured in all three years. Capture rates exist for the Desolation-Gray Canyon reach
only because within year recaptures were observed; those ranged from 0.008–0.04 and were
slightly higher than those in the middle Green River but lower than those in the lower Green
River. In the middle Green River, only five razorback suckers were recaptured across years: 3
from 2006 to 2007 and 2 from 2007 to 2008. Overall, capture rates for all reaches were highest
in 2006 (0.02–0.07), very low in 2007 (0.008–0.01), and intermediate in 2008 (0.01–0.04).
Capture rates for Colorado pikeminnow in the same reaches and years were also highest in 2006,
but tended to be higher in 2007 than 2008 (Bestgen et al. 2010). River flow rates were low in
2007, which may have made sampling more difficult, and in at least one reach, effort (in terms of
days of sampling) was relatively low.
Abundance estimates of razorback suckers varied dramatically across years in each reach
(Table 8, abundance estimates). Abundance was highest in the lower Green River, ranging from
nearly 1600 fish in 2006 to 5153 in 2007, and then declining to 2597 in 2008. Razorback sucker
abundance was lowest in the Desolation-Gray Canyon reach of the Green River, ranging from
nearly 474 fish in 2006 to 3011 in 2007, and then declining to 836 in 2008. Abundance was
intermediate in the middle Green River reach, ranging from nearly 600 fish in 2006 to 3146 in
2007, and then declining to about 1200 in 2008.
Razorback sucker abundance estimates were relatively imprecise in all reaches and years.
Abundance estimates for Green River razorback suckers in the period 2006–2008 were the most
precise in the lower Green River, with CV’s of 22–37% among years, and reflected the relatively
higher capture rates in that reach. The confidence limits for abundance estimates in other
reaches were very wide and the CV’s ranged from 49 to 81%, which limits any meaningful
inference to those estimates. However, relatively precise estimates of large-river fish abundance
are possible. For example, estimates of Colorado pikeminnow in the middle Green River reach
from 2000–2003 had CV’s of 9–18% (Bestgen et al. 2007). The higher recapture probabilities
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