Study Plan - Biological Resource Responses to Fall Steady Experimental Flows Feruary 2010

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Study Plan— Biological Resource Responses to Fall Steady Experimental Flows Released from Glen Canyon Dam, 2009 -12 Background Need for Study Regulation of the Colorado River by Glen Canyon Dam has eliminated spring snowmelt flood peaks, which historically occurred from April through early July, and increased discharge in summer, fall, and winter (Topping and others, 2003). The Bureau of Reclamation (Reclamation) has released or will release experimental steady flows from Glen Canyon Dam in September and October of 2008 through 2012 (fall steady experimental flows, FSEF) to partially mimic the steady and low flows that historically occurred annually from July to March. It is hypothesized that steady flows during the fall will benefit native fishes by stabilizing and warming the nearshore habitats that are occupied by juvenile (less than 150 mm total length) life stages of endangered humpback chub (Gila cypha) (Stone and Gorman, 2006). Fall steady flows may also affect other downstream biological resources, including the food base for native and nonnative fish. The Glen Canyon Dam Adaptive Management Work Group (AMWG) requested that the Grand Canyon Monitoring and Research Center ( GCMRC) develop a science plan for investigating the effects of FSEF. Glen Canyon Dam Adaptive Management Program participants, including natural resource managers and other stakeholders, want to know if the 2008 -12 fall steady flows will affect humpback chub and other biological resources. One of the tenets of adaptive management is that learning about managed ecosystems can and should be gained by monitoring ecosystem responses to management actions (Williams and others, 2007; Souchon and others, 2008). Additionally, evaluation of natural resource responses to the 2008 -12 FSEF is required by a 2008 environmental assessment (EA) (U.S. Department of the Interior, 2008). The studies outlined here will examine the effects of FSEF on downstream biological resources to advance adaptive management and ensure compliance with Federal environmental regulations. Provisions of the Environmental Assessment and Biological Opinion In February 2008, Reclamation released an EA (U.S. Department of the Interior, 2008) that built upon an earlier environmental impact statement for Glen Canyon Dam operations (U.S. Department of the Interior, 1995). The 2008 EA describes two flow experiments: (1) a 60 -hour experimental high -flow release from Glen Canyon Dam in March 2008 and (2) steady releases in September and October of 2008 through 2012. The exact release volumes of the second experiment (FSEF) were not specified in the 2008 EA. As a result, in addition to examining the effects of the FSEF on biological resources, the GCMRC was asked by the AMWG to make recommendations for the volume of the fall steady flows, which are presented here. Recommendations for flows needed to evaluate whether a change in the lower limit of discharge, which, since 1996, has occurred between August and September, are also provided.