Laserfiche WebLink
<br />Proposed Water Year 2005-2006 Experimental Actions <br /> <br />10 <br /> <br />particularly of fry and fingerlings, habitat modification concomitant with stage changes, <br />and erosion of benthic algae and invertebrates resulting in increased drift during the <br />period of increasing current velocities whether it occurs in November-December or <br />January, Since the high flow can occur under either the No Action or Proposed Action <br />alternative, differences in effect are restricted to those attributable to the liming of the <br />event, and these differences are expected to be minor, <br /> <br />Non-native Fish Suppression Flows <br /> <br />Korman and others (2004) have demonstrated that fluctuating flows of 5,000-20,000 cfs <br />increased incubation mortality of rainbow trout (RBT) in the Lees Ferry reach by 23%- <br />33% above Record of Decision fluctuating flows in 2003-2004. They estimated that <br />incubation mortality could have been increased to 40% had the non-native fish <br />suppression flows been conducted through April, rather than ceasing them at the end of <br />March, but that inclusion of the first week of April would result in only a minor increase <br />in mortality, <br /> <br />There was minimal reproduction of RBT in Marble Canyon in 2004 based on a <br />comparison of young-of-year densities in the reach with those in Glen Canyon, <br />Therefore, the effects of non-native fish suppression flows likely were greatest in the <br />reach of the Colorado River above the Paria River, <br /> <br />Mechanical Removal of Non-native Fish <br /> <br />Mechanical remo\'a\ would occur only under the Proposed Action. Results from the <br />ongoing removal effort for 9 trips Oan - Mar 2003, July - Sept 2003, and Jan - Mar 2004) <br />indicate that removal has a 50% efficiency for RBT and that consistent removal can have <br />a persistent effect on this species' abundance in the removal area (Coggins and Yard <br />2004), The pattern of removal efficiency is not as consistent for brown trout (BNT), <br />Predation on endangered HBC has been documented for both trout species, thus <br />reduction in their numbers in the area of the Colorado River having highest numbers of <br />the endangered cyprinid is anticipated to produce a positive effect. <br /> <br />Humpback Chub <br /> <br />Alternating Low Steady and Low Fluctuating Flows <br /> <br />Under the Proposed Action, these releases are intended to provide an opportunity to <br />measure differences during differing hydrologies in sediment transport and in near <br />shore rearing habitats of native fish, They would only occur under No Action if <br />sediment input from the Paria River exceeded 500,000 metric tons by July 1, Therefore, <br />there is a greater opportunity to learn the effects of these flows under the Proposed <br />Action, <br />