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3.2.1 Colorado pikeminnow <br /> Low numbers of Colorado pikeminnow were captured in the Yampa River during population <br /> estimation sampling in 2011-2013. Bestgen et al. (2013,p.4) states, "Captures were particularly <br /> low in the Yampa River, where only six Colorado pikeminnow were captured, in spite of high <br /> effort associated with northern pike and smallmouth bass removal sampling, as well as regular <br /> Colorado pikeminnow sampling passes (up to eight sampling passes)." And for 2013, only 8 <br /> Colorado pikeminnow were captured in the Yampa River, in spite of high effort, once again. <br /> Preliminary population estimates based on these captures are shown in Figure 7. <br /> A somewhat higher number of Colorado pikeminnow currently occupy the White River. <br /> Captures in the White River during population estimation sampling between 2011-2013 ranged <br /> from 50-96 fish (Bestgen et al. 2013). Final population estimates based on these captures are not <br /> yet available. However, numbers of Colorado pikeminnow have been larger in the past. Adult <br /> Colorado pikeminnow abundance estimates in the White River declined from 1,115 animals in <br /> 2000 to 465 animals in 2003. Adult Colorado pikeminnow resident to the White River are <br /> known to spawn in the Green and Yampa rivers. However, in 2011,researchers documented for <br /> the first time Colorado pikeminnow spawning in the White River. Juvenile and subadult <br /> Colorado pikeminnow also utilize the White River on a year-round basis (Recovery Program <br /> 2015). <br /> As part of the process of revising the 2002 Colorado Pikeminnow Recovery Goals into recovery <br /> plans, a recovery team for Colorado pikeminnow was assembled in late 2012 consisting of <br /> species and threat experts. During initial discussions in November 2012, the Recovery Team <br /> linked persistent low densities of adult Colorado pikeminnow in the Yampa River to persistent <br /> high densities of nonnative predators (e.g., smallmouth bass and northern pike; northern pike <br /> abundance shown in Figure 7). These estimates,which indicate that northern pike are <br /> outnumbering Colorado pikeminnow at least 3:1, point up the ongoing challenge of managing <br /> nonnative predators (Service 2015a). A published fish density model (McGarvey et al. 2010) <br /> supported the importance of competition among top predators in lotic systems and suggested that <br /> partitioning available energetic resources among multiple predator species would inevitably <br /> reduce carrying capacity for Colorado pikeminnow. Examination of historic and recent trends in <br /> densities of large-bodied Colorado pikeminnow, northern pike, and smallmouth bass in the <br /> middle Yampa River suggests that large-bodied invasive predators have functionally replaced <br /> Colorado pikeminnow as the river's top predator(Martinez et al. 2014). <br /> The number of adult Colorado pikeminnow residing in the Yampa River has been greatly <br /> reduced, largely because of persistent high densities of nonnative predators, and perhaps also <br /> because of extended drought(Recovery Program 2015). The Recovery Program initiated a <br /> campaign to remove nonnative predators from the critical habitat reaches of the Yampa River in <br /> the early 2000s when it became apparent that smallmouth bass were decimating the native fish <br /> populations (Anderson 2005). Since that time removal efforts have increased both <br /> geographically (now encompassing— 170 miles of Yampa River+ Catamount Reservoir) and in <br /> intensity (with some reaches receiving more than 10 removal passes/yr). <br /> 35 <br />