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GIS database and other surveys will be used to stratify habitat into classes such as talus slopes, <br />open sand bars, vegetated sand bars, cobble bars, and backwaters. We hypothesize that unstable <br />habitat types (sand bar - mediated backwaters) will be used only minimally during the summer - <br />unsteady flow period, but that use of these habitats will increase during the fall- steady period <br />when flows are stabilized. If this difference in habitat use were ecologically important, we would <br />also predict increase in growth and survival during the fall- steady flow period relative to the <br />summer because habitats may offer more favorable conditions, such as food and higher <br />temperature. <br />Effects of Fall Steady Flows on Native Fish Habitat Use. Any mark - recapture approach to <br />estimating abundance and density depends on recapturing sufficient numbers of marked <br />individuals to draw inferences on the parameters of interest. Closed population models generally <br />have fewer parameters (and assumptions) than open models and are thus better able to estimate <br />parameters of interest (capture probability and abundance) when recaptures are low. We will <br />evaluate the closure assumption in our mark - recapture experiments using methods similar to <br />Korman and others (2009). Additionally, recaptures of fish marked on previous trips will <br />provide useful information on growth and movement (e.g., movement into backwaters during <br />periods of steady flow) between sampling trips and associated flow conditions. The nearshore <br />ecology project pilot sampling data from 2008 should provide some information on closure and <br />also provide information on capture probability which is necessary to fully assess how violation <br />of the closure assumption biases abundance estimates. This project will evaluate occupancy <br />models (MacKenzie and others, 2005) and sonic tags to support habitat use assessment. This <br />project will utilize otoliths (inner ear bones) from native fishes, such as flannelmouth sucker and <br />humpback chub to investigate habitat use and origin of fish by using microchemistry to identify <br />unique isotopes. Otoliths may also prove useful for determining growth and survival rates of <br />humpback chub and other fishes. <br />Links /Relationships to Other Projects <br />This project utilizes habitat information developed largely by the GCMRC Physical Sciences and <br />Modeling and the Data Acquisition, Storage, and Analysis (DASA) programs. The results of this project <br />will help evaluate responses of small size classes of fish to various dam release flows, and so will <br />provide some of the information needed to assess the status and trends of humpback chub in the <br />mainstem Colorado River. <br />Logistics <br />This project will utilize four trips, one each in July, August, September, and October, for three years <br />(2009- 2011), subject to permit approval. All four trips are to be motor supported. The first three are <br />scheduled to launch in the motor season, but the October trip will require authority from Grand Canyon <br />National Park to use motors during the non -motor season. Sampling in October supports investigation of <br />the possible effects of steady flows on fish habitat use and so authority to conduct the trip has been <br />requested. <br />Products /Reports <br />Annual reports of project results will be delivered in December 15 of each year of the fieldwork, 2009- <br />2011. A final, synthetic report will be delivered by September 2012. <br />19 <br />