Monitoring O. mykiss Life Stages on the Stanislaus River

This study is designed to partly address steelhead conservation measures outlined in the U.S. Bureau of Reclamation's Proposed Action for the Long-Term Operation of the CVP. This effort is funded under the Central Valley Project Improvement Act (CVPIA) authority Provision 3046 (g)(4), which states the primary purpose of this effort shall be to support the Secretary's efforts in fulfilling the requirements of this title through improved scientific understanding concerning, but not limited to, measures needed to restore anadromous fisheries to optimum and sustainable levels in accordance with the restored carrying capacities of Central Valley rivers, streams, and riparian habitats.

Conceptual and quantitative work described in this report encompass multiple O. mykiss life-stages and transitions among life stages. The geographic scope of the report extends from Goodwin Dam to the confluence of the Stanislaus and San Joaquin Rivers.

The goal of this study is to develop a framework for monitoring O. mykiss life stages, and transitions among life stages, to quantify how water project operations and environmental variation influence life history expression, abundance, and population productivity. Here we provide results from activities during the base year of the Project.

• Task 1 Steelhead Monitoring Plan: Define methods and objectives for long-term O. mykiss monitoring in the Stanislaus River drainage by developing a Steelhead Monitoring Plan.
• Task 2 Enumerate the O. mykiss population size in the Stanislaus River.
• Task 3 Age and Growth Study: Estimate key population demographics (e.g., age structure, sex ratio).
• Task 4 Monitoring Instream and Outmigration Survival, and Outmigration Rate: Quantify the survival and transition probabilities of key life stages (e.g., instream rearing, outmigration survival).

The completed dataset for the 2021-2023 portion of the Project includes several components:

1. Electrofishing and seining: In 2021-2023 electrofishing, seining, and hook and line sampling of captured fish occurred opportunistically by CFS staff as well as by volunteer anglers.

2. PIT tagging: PIT tag detection records are included in the dataset after being filtered for false detections.

3. Egg to Fry Survival: Data related to the construction of artificial redds, deployment of egg boxes, and their subsequent retrieval are included in the dataset.

4. Species Counts and Physical Attributes: The species and the number caught are included in the dataset. For some O. mykiss individuals caught, the weight and fork length measurements are included. Whether or not a genetic sample (either fin clip or scale) was taken is indicated as well.

5. Rotary Screw Trap: Data related to rotary screw trap sampling are included in the dataset. This includes, but is not limited to, the environmental and metadata regarding sampling events as well as species ID, counts, recaptures, and mortalities.

6. Acoustic monitoring: Data collected by acoustic receivers from fish tagged by CFS and other agencies are included in the dataset after being filtered for false detections.

7. Supplementary Data: Data reporting field staff, weather, water temperature, electrofishing settings, and collection method used are included for greater context.

Data is recorded in a combination of paper to computer files and electronic only files. Annual reports summarize the survey findings. While this project is ongoing, this is a completed dataset for the collection sessions performed in the year 2023.