Western Washington University Western CEDAR WWU Graduate School Collection WWU Graduate and Undergraduate Scholarship 2014 Dietary characteristics of juvenile trout and char in seasonally inundated stream segments in Ross Lake, Washington Emily Derenne Western Washington University Follow this and additional works at: https://cedar.wwu.edu/wwuet Part of the Environmental Sciences Commons Recommended Citation Derenne, Emily, "Dietary characteristics of juvenile trout and char in seasonally inundated stream segments in Ross Lake, Washington" (2014). WWU Graduate School Collection. 382. https://cedar.wwu.edu/wwuet/382 This Masters Thesis is brought to you for free and open access by the WWU Graduate and Undergraduate Scholarship at Western CEDAR. It has been accepted for inclusion in WWU Graduate School Collection by an authorized administrator of Western CEDAR. For more information, please contact [email protected]. DIETARY CHARACTERISTICS OF JUVENILE TROUT AND CHAR IN SEASONALLY INUNDATED STREAM SEGMENTS IN ROSS LAKE, WASHINGTON By Emily Derenne Accepted in Partial Completion Of the Requirements for the Degree Master of Science Kathleen L. Kitto, Dean of the Graduate School ADVISORY COMMITTEE Chair, Dr. Leo Bodensteiner Dr. James Helfield Ashley K. Rawhouser MASTER’S THESIS In presenting this thesis in partial fulfillment of the requirements for a master’s degree at Western Washington University, I grant to Western Washington University the non-exclusive royalty-free right to archive, reproduce, distribute, and display the thesis in any and all forms, including electronic format, via any digital library mechanisms maintained by WWU. I represent and warrant this is my original work, and does not infringe or violate any rights of others. I warrant that I have obtained written permissions from the owner of any third party copyrighted material included in these files. I acknowledge that I retain ownership rights to the copyright of this work, including but not limited to the right to use all or part of this work in future works, such as articles or books. Library users are granted permission for individual, research and non-commercial reproduction of this work for educational purposes only. Any further digital posting of this document requires specific permission from the author. Any copying or publication of this thesis for commercial purposes, or for financial gain, is not allowed without my written permission. Emily Derenne November 10, 2014 DIETARY CHARACTERISTICS OF JUVENILE TROUT AND CHAR IN SEASONALLY INUNDATED STREAM SEGMENTS IN ROSS LAKE, WASHINGTON A Thesis Presented to The Faculty of Western Washington University In Partial Fulfillment Of the Requirements for the Degree Master of Science By Emily Derenne November 2014 Abstract I investigated available prey items and the diet characteristics of juvenile fishes in three seasonally inundated tributaries to Ross Lake, Washington from March through June, 2013. Native fishes include Rainbow Trout (Oncorhynchus mykiss), Bull Trout (Salvelinus confluentus), and Dolly Varden (Salvelinus malma). Cutthroat Trout (Oncorhynchus clarkii), Brook Trout (Salvelinus fontinalis) and Redside Shiner (Richardsonious balteatus) comprise the introduced fishes in the lake. Both Cutthroat Trout and Redside Shiner are native to Washington, but not Ross Lake. Juvenile Bull Trout, Rainbow Trout, and Brook Trout are known to feed on items along the bottom of lakes or streams, such as larval and adult insects as well as items floating or drifting in the water column. Diet composition can be altered by the benthic macroinvertebrate community, season, and habitat type as well as anthropogenic interferences such as dams. During each sampling event the stream was electrofished, benthic macroinvertebrate samples were collected, all captured fish over 50 mm were lavaged, and during the initial visit to each site, a habitat assessment occurred. Three fifty-meter reaches were selected for each stream to have representative sites at low, medium, high, and full pool elevations. Rapid habitat assessment was completed following USFS Stream Inventory Handbook for Region 6 on each of the streams during the first site visit, benthic macroinvertebrate sampling followed a modified version of the Environmental Protection Agency’s Rapid Bioassessment Protocols for Use in Streams and Wadeable Rivers: Periphyton, Benthic Macroinvertebrates, and Fish, electrofishing followed American Fisheries Society and National Marine Fisheries Service Guidelines, and diet evaluation was completed using non-lethal gastric lavage of stomach contents mm following the modified protocols of Giles (1980), Strange and Kennedy (1981), Hartleb and Moring (1995). My study suggests adequate food, in the form of benthic macroinvertebrates, is present based on the presence of few fish with empty stomachs in the system. The benthic macroinvertebrates found in the tributaries to Ross iv Lake reflect those commonly found in Pacific Northwest Streams. A total of 3,645 individuals in 31 families were collected. Ephemeroptera was the most abundant and frequently occurring insect order across all samples, but not uniformly the most abundant at all sites, dates, or months. Abundance of families by date differed, but not site or reach. Diets varied by sites, months, and most pool elevations, but not species. Sixty-five of the seventy-three fish collected had at least one diet item in their stomach (89% off all fish). Including those taxa that were identifiable only to terrestrial origin or class Insecta and those unrecognizable even at the class level, there were sixteen categories for analysis, seven of which were considered major and included in all analyses. Using Index of Relative Importance, I determined Diptera was the most important prey item overall, followed by Ephemeroptera. Stomach fullness, calculated by Instantaneous Ration, was correlated to the number of prey found in individual fish stomachs. As expected, stomach fullness followed benthos abundance trends. Many studies are completed on adult feeding strategies, especially in comparisons between species or environments, but research on juvenile diets is less available, and to the best of my knowledge research on prey availability and selectivity on seasonally inundated streams is non-existent. Further research on Ross Lake juvenile trout diet, the most important prey taxa, and the benthic community they rely on will result in a better understanding of fish stock dynamics and Ross Lake ecology and perhaps influence management of the fish stocks and lake levels in the future. v Acknowledgements I am ever grateful to Dr. Leo Bodensteiner, my Committee chair and determined advisor. He attended every field visit and spent immeasurable hours looking at difficult to identify invertebrates with me. I’d like to thank my committee members Ashley Rawhouser for his help in the field and use of the boat and Dr. James Helfield for wading through the PRIMER software with me. I could not have completed this research without great volunteers. I am very thankful for: Laura Junge and Brian Podobnik, in the field and Sage Presseter in the lab; Erin Morgan of the University of Washington Wetland Ecosystem Team for teaching me to lavage; Bob Wisseman for performing quality control on my collected samples; and Wendy Cole and Denise Krownbell for passing along relevant studies and reports from their agencies that were unpublished or difficult to locate. Throughout this study, Matt Bain assisted in the field, and more importantly provided support, encouragement, and often motivation; my sincere thanks. Funding for this research was provided by: Huxley College of the Environment Puget Sound Anglers: Fidalgo – San Juan Chapter. vi Table of Contents Abstract ..................................................................................................................................................................... iv Acknowledgements ................................................................................................................................................... vi List of Tables ............................................................................................................................................................ viii List of Figures ............................................................................................................................................................. ix Introduction ................................................................................................................................................................ 1 Methods ................................................................................................................................................................... 11 Results ...................................................................................................................................................................... 24 Discussion ................................................................................................................................................................. 41 Conclusion ................................................................................................................................................................ 50 Literature Cited....................................................................................................................................................... 100 vii List of Tables Table 1. Ross Lake reservoir