This fast track project will provide high precision population status and trend information for Imnaha River steelhead. Information regarding Snake River steelhead is considered a high priority for informing managers .  Population abundance and productivity data are used by multiple entities in the Columbia Basin (e.g. assessing ESA listing status, harvest season opportunities, and effectiveness of management actions).  Most important is the ability to describe a population’s abundance relative to management goals, quasi-extinction thresholds, sustainable harvest, and ecological process.  The Imnaha River steelhead population is unique in the Snake River DPS in that it: 1) is physically small enough to conduct sampling of steelhead (mainstem flow and manageable number of spawning/rearing aggregates), 2) has a dendritic structure of spawning areas occurring across the entire range of elevations available to Snake basin DPS steelhead (spawning in areas from 1,000 feet up to 6,000 feet), and 3) has a supplementation program occurring in just two of its spawning aggregates.

This project will use data collected from a variety of monitoring techniques including floating weirs, fixed weirs, and PIT tag arrays throughout the Imnaha River drainage.  NPT staff will deploy two customized weirs and 4 small PIT tag arrays  in the upper tributaries of the Imnaha River that serve as spawning grounds for the endemic steelhead of the subbasin (Camp, Freezeout, Summit, Grouse, Crazyman, Mahogany and Gumboot). The ISEMP project (BPA Project No. 200301700) is also a fast track proposal that will install two PIT tag arrays in lower Imnaha River and two arrays in the upper mainstem Imnaha River and Big Sheep Creek.  Biomark, Inc. will serve as the subcontractor to deploy these arrays. NPT staff will assist Biomark, Inc. with site selection and deployment of PIT tag arrays in the upper mainstem Imnaha River and Big Sheep Creek. These arrays will be relied upon with their representative PIT tagging of Snake basin DPS adult steelhead at Lower Granite Dam to provide one measure of steelhead population escapement to the Imnaha River.  Weirs will monitor adult fish passage and distribution from February through June, while PIT tag arrays will operated year around.  We will incorporate results from these efforts and other monitoring results conducted under the Lower Snake River Compensation Program for a comprehensive understanding of the Imnaha steelhead population.

Given the desire for escapement data, hatchery composition, and age structure information on the population, physically handling of a portion of the run is necessary to enable biological sampling.  This project will provide high accuracy and precision escapement estimates to Imnaha tributaries hatchery fraction, age structure, age-at-return, size-at-return, age-at-emigration, percent females, adult run-timing, and within population spatial structure/distribution.

The Regional RM&E Collaboration strategies for Snake River basin spring/summer Chinook and steelhead call for high precision estimates of adult abundance (coefficient of variation of 15% or less) in at least one population per life history type per Major Population Group. High precision priority populations identified included Imnaha River steelhead (Coordinated Anadromous Workshop 2010).  In addition, adult abundance data from these populations was identified as necessary to fulfill Federal Columbia River Power System RPAs: 50.5 (CAA/NOAA/NPCC RM&E Workgroup 2009 and Coordinated Anadromous Workshop 2010).