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

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Data Synthesis and Integration We will use several lines of evidence to determine whether humpback chub benefit from stable flows in September and October because of the significance and importance of this issue. Over the next 5 years, there will be hourly variation in flow rates (related to diel variations in energy demand) during summer months (modified low fluctuating flows, MLFF, June through August) and lower, steady experimental flows during the fall (FSEF, September and October). The centerpiece of this data synthesis and integration is the nearshore ecology project (Project 1), which seeks to determine the use and relative importance of nearshore habitat to humpback chub and other fishes and addresses strategic science questions (SSQs) 1. 1, 1.7, 4.2, 5.4, and 5.6. This project will quantify abundance, survival, habitat use, growth, and natal source of selected native and nonnative juvenile fish over two flow periods (summer MLFF and FSEF). This project will evaluate humpback chub response by measuring differences in static measurements (catch rate, abundance, and occupancy data) and process -level measurements (proxies for fish growth — otolith daily increments, RNA /DNA ratios) during fluctuating flows of July and August relative to these same measurements during stable discharge in September and October. These measurements will evaluate the short-term effect of interactions between flow, fish habitat selection, and growth, and will help inform analysis of humpback chub recruitment trends. Because of the importance of the nearshore ecology project, a complete project description is presented in appendix A. If stock- assessment analysis (Project 2) finds that humpback chub recruitment trends from cohorts spawned during 2008 through 2012 are strongly positive, this may provide support that steady flows in September and October benefit humpback chub. During the remaining years of the experiment there are likely to be differences in annual volumes, tributary activity, and other factors that will affect humpback chub recruitment success and may confound data interpretation. As such, we propose that the same stable discharge occur the remaining years of the experiment to minimize the number of confounding factors that will complicate interpretation of these recruitment data. We are not evaluating interactions between native and nonnative fish (that is, competition and predation) because previous studies have evaluated these interactions (Yard and others, in press; Kennedy and others, U.S. Geological Survey, unpub. data, 2010), and we do not expect there to be a strong interaction between the proposed July – October flows and competition or predation. Yard and others (in press) found turbidity had a strong influence on the degree of piscivory by rainbow trout, and tributary activity will have a far greater impact on turbidity than steady flows. Further, the nearshore ecology project pilot study attempted to quantify differences in predation risk among habitat types and across flows in August and September 2008, but the results Were inconclusive and the work was extremely time consuming. Thus, our humpback chub projects focus on studying the short -term interactions between flows, habitat use, and fish growth, and the long -term effect of these interactions on recruitment. Food base data (Project 3) will provide additional insights into mechanisms underlying any native fish response and seeks to determine whether and to what degree flow regimes impact the rates of primary production and /or invertebrate drift. Project 3 specifically relates to SSQ 3.5. The food base project focuses on process -level measurements at locations that are easy to access (Lees Ferry and Diamond Creek). Frequent measurement of these parameters, which is only possible at easy to access locations, will greatly increase the strength of our inferences with respect to flow. Work in Lees Ferry will be especially informative because tributary sediment and carbon inputs, which have a far greater impact on 13