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

using open population model (no assumption of demographic closure of populations) Cormack-
Jolly-Seber estimation procedures. It is also possible to obtain estimates of annual transition
rates of fish between sampling reaches if the sampling design supports a multi-state model
analysis. Additional sampling between primary three-year sampling blocks sometimes allows
for estimation of population rates of change (λ) that determine if population abundance (not
estimated directly) is increasing, decreasing, or staying the same by essentially comparing
survival and recruitment rates.
Conveniently, population centers for razorback suckers in the Upper Colorado River
Basin are mostly overlapped by sampling areas for Colorado pikeminnow. This is particularly
true in the Green River Basin, because substantial captures of adult razorback suckers have
occurred mainly in the mainstem Green River, with a few in the lower White River (e.g., 2011).
Substantial numbers of razorback suckers do not occur in tributaries such as the San Rafael
River, or the Green River upstream of the Yampa River, or the Yampa River itself, even though
scattered individuals are occasionally found in those places. Instead, most captures have been in
the mainstem Green River from downstream of Split Mountain boat ramp downstream to the
confluence with the Colorado River. A similar situation exists in the Colorado River, where
Colorado pikeminnow sampling areas broadly overlap with known distribution of stocked adult
razorback suckers from just upstream of the confluence of the Gunnison and Colorado rivers
downstream to the confluence with the Green River (Zelasko 2008; Osmundson and Seal 2009;
Zelasko et al. 2010).
Green River data, fish distribution, and macrohabitat use. —Because of broad overlap of
sampling areas, monitoring population status of razorback suckers will borrow heavily from
sampling for Colorado pikeminnow, since many razorback suckers are captured during that
sampling (Table 2, captures by sampling program, 2006–2008 data). For example, of 1,177
razorback sucker captures in the Green River Basin during 2006–2008, 1,079 (92%) were made
during sampling for Colorado pikeminnow abundance estimation. Spring Colorado pikeminnow
sampling is also conducted when razorback suckers may be most susceptible to capture, because
they are in relatively shallow water near or at spawning areas.
Additional razorback suckers were captured in the 2006–2008 period in the Green River
during humpback chub Gila cypha sampling (n = 11), and northern pike Esox lucius and
smallmouth bass Micropterus dolomieu removal sampling (n = 16 and 71, respectively), but
those contributions are small relative to captures during pikeminnow sampling; such additional
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