9560 - Laserfiche WebLink

Home Browse Search

9 I I I I I I I I I I I I :1 'I I I I I I Parachute, Colorado (Valdez et al. 1985), showed that drifting larval densities near the shoreline were seven times greater than mid-channel densities. These data were inconclusive, but suggest that larvae are uniformly mixed in the water colwnn. One estimate of larval entrainment is to estimate the volume of water entering a floodplain as a percentage of total river volume and assume an equal percentage of total drift. However, if larval densities are highest along the shoreline, the assumption of thorough river-wide mixing could underestimate the percentage and larvae entrained. 3.8 Growth in Floodplains Growth rates of young razorback sucker were taken from various studies (Modde 1996, 1997; Muth and Wick 1997; Muth et al. 1998). Additional information on growth of young razorback sucker is available from lower basin studies (Minckley et al. 1991). 3.9 Survival in Floodplains Recent investigations in floodplains along the Green River show low survival rate of larval razorback sucker (Birchell and Christopherson 2002; Christopherson and Birchell 2002). Larvae stocked into the Stirrup floodplain in May 2002 were resampled in late July and early August with a survival rate of 0.40/0-0.7% in uncontrolled areas with adult fathead minnows (Pimephales promelas), red shiners (Cyprinella lutrensis), black bullheads (Ameiurus melas), green sunfish (Lepomis cyanellus), and common carp (Cyprinus carpio). Survival in controlled conditions that excluded these nonnative predators and competitors was 12.0%. Survival oflarval razorback sucker has also been assessed in outdoor earthen ponds and under experimental conditions. Hamman (1987) reported 94.5% survival oflarvae after 120 days in earthen ponds; this equates to 84.4% over 12 months, 71.2% over 24 months, and 60.1 % over 36 months. Papoulias and Minckley (1990) reported 89.9% survival of razorback sucker larvae after 30 days in controlled conditions; this equates to 27.9% over 12 months, 7.8% over 24 months, and 2.2% over 36 months. Papoulias and Minckley (1990) also reported 67.4% minimal survival of razorback sucker larvae after 30 days; this equates to O.goAl over 12 months, 0.01 % over 24 months, and 0.0001 % over 36 months. 3.10 Residence Time in Floodplains The amount of time that a razorback sucker spends in a floodplain depends on a number