Steelhead Survival and Population Viability Assessment Study

Strategic planning and effectiveness monitoring of habitat restoration is needed to identify the best methods and locations given the life stage(s) to provide benefits for targeted fish species. Tracking survival and potential shifts of various steelhead life history strategies are important for measuring success of restoration actions. Currently, there is a lack of unified framework to tie habitat restoration to juvenile steelhead growth, survival, and age structure in a way that shows how actions affect population viability. This information is needed to truly monitor the effectiveness of habitat restoration.



This project will develop methods to estimate and track survival of wild juvenile steelhead in select key subwatersheds and watersheds in Idaho to Lower Granite Dam. The study will investigate trends in survival of different juvenile life history strategies by age and by movement strategies. IDFG will also estimate and track brood year survival and abundance of smolts to Lower Granite Dam. Findings can then be associated to habitat conditions and be used to construct better guiding documents for planning and implementing habitat restoration for wild steelhead.



Size, age, movement, and survival of wild juvenile steelhead will be evaluated among all existing life history strategies and for assessing brood year cohort survival to Lower Granite Dam using fish PIT-tagged at various screw trap sites across Idaho, focusing on the existing Intensively Monitored Watersheds. This project will integrate age information and abundance estimates obtained at screw traps to provide levels of uncertainty for overall brood year smolt survival and abundance estimates.



This work will mostly be a quantitative exercise requiring a computer and programs capable of building and analyzing complex modeling. The exercise will use existing PIT tag and detection information that will be extracted from the Columbia Basin PIT Tag Information System (PTAGIS), size and age information extracted from the IDFG database that houses all the age information for PIT-tagged fish that were aged, and screw trap abundance estimates generated from IDFG. Sensitivity analyses will be conducted to test for error and biases of inputs to the model that will include assigning ages to fish, trapping efficiencies of screw traps, sample sizes of PIT-tagged fish, and detection probabilities.



The outputs from the developed model and potential applications will provide a timeseries of length-at-age, life history strategies of wild steelhead, proportions of those life history strategies identified at the subwatershed or watershed scales, survival of the different life histories, contributions of life histories to smolts that survived, and overall brood year cohort survival and abundance to Lower Granite Dam with uncertainty.

Inferences on restoration benefits to steelhead population viability are lacking due to their complex life history. The goal of this project will be to examine life history characteristics of wild juvenile steelhead and how they contribute to smolts that survive to Lower Granite Dam. Links can be made between habitat conditions and survival by different life stages to better understand limiting factors in freshwater systems.



This project will leverage previous PCSRF investments and specifically link them to habitat restoration benefits to steelhead. Changes in life history strategies and survival will assess potential success or failures of restoration actions at multiple spatial scales (e.g., subwatershed, watershed, large basin or catchment). Further analyzing relationships of life history strategies and survival to habitat conditions can help inform future modeling methods for predicting population-level response given a suite of proposed actions (e.g., integrated or life cycle models; Jorgensen et al. 2021). Thus, there will also be benefits to viability assessments.