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2.1.2 Life history <br /> The Colorado pikeminnow requires relatively warm waters for spawning, egg incubation, and <br /> survival of young. Males become sexually mature at approximately 6 years of age,which <br /> corresponds to a length of about 400 millimeters (mm) (17 inches (in.)), and females mature 1 <br /> year later(Sigler and Sigler 1996). <br /> Mature adults migrate to established spawning areas in late spring as water temperatures begin to <br /> warm,with migration events up to 745 river kilometers round-trip on record (463 mi) (Bestgen et <br /> al. 2005). Spawning typically begins after peak flows have subsided and water temperatures are <br /> above 16' Celsius (°C) (60.8° Fahrenheit ff)). Mature adults deposit eggs over gravel substrate <br /> through broadcast spawning and eggs generally hatch within 4 to 6 days (multiple references in <br /> Bestgen et al. 2005). River flows then carry emerging larval fish (6.0 to 7.5 mm long (0.2 to 0.3 <br /> in.)) downstream 40 to 200 km to nursery backwaters (25 to 125 mi),where they remain for the <br /> first year of life (Service 2002b). <br /> Colorado pikeminnow reach lengths of approximately 70 mm by age 1 (juveniles) (2.8 in.), 230 <br /> mm by age 3 (subadults) (9 in.), and 420 mm by age 6 (adults) (16.5 in.),with mean annual <br /> growth rates of adult and subadult fish slowing as fish become older (Osmundson et al. 1997). <br /> The largest fish reach lengths between 900 and 1000 mm (35 to 39 in.); these fish are quite old, <br /> likely being 47 to 55 years old with a minimum of 34 years (Osmundson et al. 1997). <br /> Reproductive success and recruitment of Colorado pikeminnow is pulsed,with certain years <br /> having highly successful productivity and other years marked by failed or low success (Service <br /> 2002b). The most successful years produce a large cohort of individuals that is apparent in the <br /> population over time. Once individuals reach adulthood, approximately 80 to 90 percent of <br /> adults greater than 500 mm (20 in.) survive each year(Osmundson et al. 1997; Osmundson and <br /> White 2009). Strong cohorts,high adult survivorship, and extreme longevity are likely life <br /> history strategies that allow the species to survive in highly variable ecological conditions of <br /> desert rivers. <br /> 2.1.3 Population Dynamics <br /> The Colorado pikeminnow is endemic to the Colorado River basin,where it was once <br /> widespread and abundant in warm-water rivers and tributaries. Wild populations of Colorado <br /> pikeminnow are found only in the upper basin of the Colorado River(above Lake Powell). <br /> Three wild populations of Colorado pikeminnow are found in about 1,090 miles of riverine <br /> habitat in the Green River,upper Colorado River, and San Juan River subbasins (Service 2011 a). <br /> We measure population dynamics of Colorado pikeminnow separately in the Green, upper <br /> Colorado, and San Juan River basins because distinct recovery criteria are delineated for each of <br /> these three basins. In the 2002 recovery plan, preliminary abundance estimates for wild adults in <br /> the basins were: upper Colorado River, 600 to 900; Green River, 6000 to 8000; and San Juan <br /> River, 19 to 50 (Service 2002b). <br /> 7 <br />