The use of rotary screw traps (RSTs) has become an essential tool for biologists to assess downstream migration timing and estimate abundance of juvenile salmon and steelhead. Rotary screw traps are operated at a fixed location for extended periods of time, and when properly operated, can provide credible estimates of juvenile abundance. The Yuba Reintroduction Working Group (YRWG), a collection of State and Federal agencies, NGOs, the Yuba Water Agency, and other stakeholders, is focused on investigating the biological, technical, and financial feasibility of reintroducing spring-run Chinook salmon (Oncorhynchus tshawytscha) to historical spawning habitat in the upper Yuba River Watershed. To assist with data collection for this effort, FISHBIO was tasked with assessing how effectively RSTs will collect emigrating juveniles once they are reintroduced, and whether RSTs can be safely operated at a range of flows on the North Yuba River.
The RST at Rocky Rest.
The North Yuba River – the largest of the three main tributaries of the Yuba River – flows through the towns of Sierra City, Downieville, and Goodyears Bar, and eventually empties into New Bullards Bar Reservoir. Upon completion of an assessment of many suitable sites in February 2023, two locations were chosen based on ease of access, safety, and channel characteristics. One of these sites is along Old Toll Bridge Rd (near Goodyears Bar), and the other is at Rocky Rest Campground. Two RST sizes underwent evaluation at Old Toll Bridge Rd site – one smaller trap with a 5-ft diameter cone, and one larger with an 8-ft diameter cone – while only one RST of the 8ft size was evaluated at Rocky Rest site.
Image 1: FISHBIO biologist explains the RST project to interested community members.
Image 2: A group of rafters pass by the RST.
FISHBIO was responsible for acquiring all necessary permits for RST installation and operations, performing the installation and deployments of the RSTs, field operations, and data analyses. Throughout both phases of the project, FISHBIO staff have routinely provided updates to the YRWG on the progress and findings. The main objectives of the evaluation are to determine the range of flows at which the RSTs can be safely and effectively operated and, based on the historical hydrology, what percentage of the juvenile migration season the RSTs could be expected to operate. The field evaluation of RST performance began in October 2023 and was completed in May 2024.
FISHBIO staff scouting potential sites for the RSTs.
RST field evaluations include routinely tracking and responding to storm events to collect relevant RST performance data at each RST site during fluctuating flow levels. To sample a flow (discharge), the RST cone is lowered into the water to “fish” for a pre-determined duration. Importantly, none of the RSTs operated during the field evaluation phase of this project are trapping or holding fish. The back mesh screen of the live well on each RST has been removed, and any fish funneled through the cone have the ability to safely exit out the back of the live well. To monitor RST performance during a “fishing” period, various types of data are recorded each time an RST is visited. These include both qualitative and quantitative data such as cone revolution rate, debris load, river stage, turbidity, water velocity, discharge, public interactions, trap status and condition, distance from the bank, and photos taken.
An interpretive sign at one of the RST sites.
These metrics allow FISHBIO to track RST performance at varying discharges and test which RST sizes can operate most effectively and safely at different positions within their site locations. Analyzing a combination of this data set and historic hydrological data at the conclusion of the evaluation is expected to reveal how much of the juvenile salmonid migration period each RST can operate, and estimate what each trap’s efficiency could be (referencing existing trap efficiency data).
Header Image: FISHBIO staff check the RST deployed near Goodyears Bar during high flows.
