Egg-to-fry survival rates for salmonids in the Green River, a key watershed for recovering Puget Sound salmonid species, lag behind those of other west-slope Cascade Range rivers. Identifying the key factors at different life stages that limit the production of offspring and adult salmon will help determine the appropriate approach for management. Stillwater Sciences worked with the Muckleshoot Indian Tribe to develop and implement a study to determine gravel quality in known spawning sites in the middle Green River and to evaluate the likely effects existing gravel quality has on current and future salmon production. The overall purpose of the project was to determine whether fine sediment is impacting survival of salmonid eggs and if there are spatial patterns that suggest likely cause(s) for observed conditions.
The primary sampling objectives of this study were to assess the fine sediment and bed-sediment composition, to evaluate their spatial distribution, and to assess their potential influence on survival-to-emergence. Stillwater scientists worked in conjunction with staff of the Muckleshoot Indian Tribe and the Washington Department of Ecology to develop a statistically robust study design that required broad geomorphic characterization of the river to inform a focused sampling regime of fine sediments associated with known spawning activity.
Stillwater geomorphologists and biologists collected and analyzed field samples from 52 sites and evaluated the effects of intra-gravel quality as it relates to potential salmon production. We also conducted a field investigation of landslide activity and recommended approaches to monitor and estimate fine sediment loading from this source over time. The results of the study will help guide future habitat protection, restoration, fisheries enhancement, and appropriate sediment-management practices.