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2.2.3 Population dynamics <br /> Population estimates during the 1980 to 1992 period were on average between 300 and 600 wild <br /> fish (Modde et al. 1996). By the early 2000s, the wild population consisted of primarily aging <br /> adults,with steep decline in numbers caused by extremely low natural recruitment(Service <br /> 2002b). Although reproduction was occurring,very few juveniles were found (Service 2002b). <br /> In the early part of the 2000s, population numbers were extremely low. Population estimates <br /> from sampling efforts in the Middle Green River had declined to approximately 100 by 2002, <br /> with researchers hypothesizing that wild fish in the Green River Basin could become extirpated <br /> because of lack of recruitment(Bestgen et al. 2002). Similarly, in the upper Colorado River, <br /> razorback sucker were exceedingly rare. In the 2002 recovery plan, razorback sucker were <br /> considered extirpated in the Gunnison River,where fish were last captured in 1976 (Service <br /> 2002b). Similarly, in the Grand Valley, only 12 fish were collected from 1984 to 1990, despite <br /> intensive sampling (Service 2002b). No young razorback sucker were captured in the Upper <br /> Colorado River since the mid-1960s (Service 2002b). <br /> Razorback sucker likely occurred in the San Juan River as far upstream as Rosa,New Mexico <br /> (now inundated by Navajo Reservoir) (Ryden 1997). In the San Juan River we know of only two <br /> wild razorback suckers that were captured in 1976 in a riverside pond near Bluff,Utah, and one <br /> fish captured in the river in 1988, also near Bluff(Ryden 2006). No wild razorback sucker were <br /> found during the 7-year research period (1991-1997) of the San Juan River Basin Recovery <br /> Implementation Program (Ryden 2006). <br /> Because of the low numbers of wild fish, the Recovery Program has been rebuilding razorback <br /> sucker populations in the upper Colorado River Basin with hatchery stocks. Since 1995, over <br /> 375,000 subadult razorback suckers have been stocked in the Green and upper Colorado River <br /> subbasins. Preliminary population estimates were generated for razorback sucker in the <br /> Colorado River as a whole (from Palisade, CO downstream to its confluence with the Green <br /> River), for adult fish> 400 mm TL (Figure 6). Although razorback sucker numbers have begun <br /> increasing in the past decade in the Green River subbasin due to stocking efforts,no standardized <br /> monitoring program to produce a population estimate has begun for the Green River subbasin <br /> (Service 2012a). <br /> 18 <br />