Assessment of Chinook Salmon Smolt Habitat Use in the lower Trinity River

This report summarizes data collections and analyses to assess variation in physical habitat characteristics selected by Chinook Salmon smolts in the Trinity River. Spatially, this study focuses on two mainstem Trinity River reaches located downstream of the confluence of the North Fork Trinity River, each several kilometers in length. This project was initiated to inform the extension of the Trinity River Stream Salmonid Simulator (S3) model from the confluence of the North Fork Trinity River to the confluence with the Klamath River.

Several methods for observing and enumerating juvenile Chinook Salmon were explored, with the goal to compliment habitat models developed for Chinook Salmon fry and parr in the upper portion of the Trinity River mainstem. Methods applying various sonar camera technologies were deemed ineffective for the intended needs of the project. To complete the project, direct-observation snorkel counts we chosen as the data collection method.

Time spent conducting field sampling methodology trials and elevated flows causing turbid waters too dark for effective sampling caused delays in implementation of the data collection. Eventually, assessments of habitat use were collected at the desired sites, but during a single week in August. The single week of sampling is generally thought to be too short to capture temporal variation in habitat use. Additionally, the August period of collection is rather late in the period of time when juvenile Chinook Salmon inhabit the Trinity River, and too few wild fish may have been present to accurately reflect the habitat selection of larger juveniles.