Lemhi River Rehabilitation Project Monitoring 2022

Over the last decade, extensive investments have been made in numerous habitat rehabilitation efforts for listed Snake River Spring/Summer Chinook salmon & steelhead in the Lemhi River. Efforts have increasingly focused on habitat capacity limitations for parr and presmolt rearing life stages. However, due to the migratory life history, it has been difficult to monitor and quantify project-scale benefits from rehabilitation efforts. Passive Integrated Transponder (PIT) technology present a novel approach to monitor the extent fish use restored habitat reaches during rearing and migration. This project will maintain existing PIT infrastructure critical for project and population-level monitoring.



Objectives include: 1) Maintain rotary screw trap (RST) tagging and increase electrofishing to expand the variation in rearing and migration strategies monitored to include fish otherwise unavailable for capture by RSTs due to migration timing. 2) Assess juvenile Chinook salmon and steelhead habitat use (e.g., timing and duration) within newly rehabilitated habitat, and 3) Quantify the effect that parr and presmolt Chinook salmon habitat use has on growth, body condition, outmigration timing, and survival to the lower Lemhi River and to the hydrosystem. Additionally, this proposal will help fund annual Chinook salmon redd surveys, operation of three RSTs, and operation of 23 PIT arrays.

The Lemhi River Rehabilitation Project Monitoring 2022 project will aid in the continued long-term tagging and monitoring of Chinook salmon and O. mykiss in the Lemhi River watershed, an ongoing intensively monitored watershed. Continued tagging efforts using rotary screw traps and electrofishing will support sample sizes necessary for analysis of movement, emigration timing, habitat use, growth, and survival for juvenile salmonids. These fish exhibit a suite of migratory tactics (e.g., downstream rearing versus natal reach rearing) and this monitoring will aid in both project-scale and population-scale effectiveness monitoring of rehabilitation actions in the Lemhi River. The operation and maintenance of Passive Integrated Transponder (PIT) array infrastructure within restoration projects in the lower Lemhi River will support monitoring of habitat use and residency of juvenile salmonids at a temporal and spatial scale not previously possible. Additionally, PIT arrays have recently been installed on the spillway weir at Lower Granite Dam; this significantly increased average detections rates by 453% for Chinook salmon and 432% for steelhead relative to detections at the juvenile bypass system alone. These increases suggest 4-5x more detections of Lemhi River juvenile emigrants at Lower Granite Dam, which allow for more accurate estimates of emigration timing and survival.