Invasive Brown Trout Population Assessment and Suppression Feasibility Pilot Study Phase 2 FY2014

This project involved a second round of Brown Trout collection 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. Captured brown trout were sampled for stomach contents, tissue samples and scales were taken for analysis to assess diet and age. In addition to data collection scales were used to calculate growth and mortality rates, and mark recapture rates were used to establish population estimates for both years of sampling. Results from this assessment will be used to illuminate the magnitude of the problem and capture success rates will inform suppression feasibility while implementing a one-time suppression treatment via fish collections. This project was conducted in close coordination with NOAA, USFWS, CDFW, the Yurok Tribe and Humboldt State University. This project was conducted by Justin Alvarez, a tribal member and employee of the Hoopa Valley Tribal Fisheries Department, and Dr. Darren Ward at Humboldt State University, as part of a masters thesis project by Mr. Alvarez.

As the study progresses we are finding that Brown Trout are consuming many Coho salmon especially age 1+ individuals. The timing of this years electrofishing efforts will provide more insight into Brown Trout diets when hatchery fish are not as available. This will allow a more clear picture as to the proportion of the various prey Brown Trout are consuming. An additional benefit is a better understanding of what time of year is best for a removal effort in any suppression actions. A more efficient removal will provide the largest benefit to ESA listed salmon with the least impact to the native fishes of the Trinity River. Activities and methods are to collect biological data on brown trout and analyze results to recommend management. A complete list of methods was provided to NOAA Fisheries for review.