Invasive Brown Trout Population Assessment and Suppression Feasibility Pilot Study Phase 1

This project involved the collection of brown trout through a variety of methods including electrofishing, angling, and capture at fish sampling weirs to provide information on trout population size, distribution, age and diet. The majority of captured brown trout had stomach contents, scales, and tissue samples taken to assess age and diet. Scales collected during these efforts as well as scales provided by CDFW were prepped for aging. Future analysis of data from this collection will be used to build a bioenergetics model to help illuminate the magnitude of the problem and capture success rates informed suppression feasibility. This project was conducted in close coordination with NOAA, CDFW, and Humboldt State University.

Brown Trout are predators of and compete with ESA listed SONCC, contributing to their imperiled state. In order to quantify the impact that Brown Trout are imposing on Coho salmon, Hoopa Valley Tribal Fisheries Department (HVTFD) began to enumerate the population of brown trout within the Trinity River, assess brown trout diet, age and habitat utilization, and develop recommendations for suppressing brown trout population to levels that do not significantly impede ESA and tribal trust species recovery. The findings of this study will provide justification for any changes in management actions concerning Brown Trout on the Trinity River. All Brown Trout captured will be used for research and/or humanely euthanized (permit dependent) as part of an initial suppression effort. The projects goals, objectives, activities and methods are listed below. Brown Trout populations have increased significantly in the upper Trinity River, confounding efforts to restore anadromous fish (Chinook salmon, Coho salmon, steelhead trout, Pacific lamprey) to pre-Dam levels as envisioned in the Trinity Record of Decision.