ANABSTRACT OFTHE THESIS OF Scott D. Lewis for the degree of Master of Science in Fisheries Science presented on 24 November 1997. Title: Life History, Population Dynamics, and Management of Signal Crayfish in Lake Billy Chinook, Oregon. Abstract approved:Signature redacted forprivacy. / '- 1 Howard F. Horton Signal crayfish Pacifastacus leniusculus were studied in Lake Billy Chinook, Oregon, during 1994 and 1995. Because little was known about the crayfish population, this study was conducted to obtain reliable estimates of life history and population parameters, document historic commercial harvests, and make management recommendations. Crayfish were captured with baited traps and by hand using SCUBA gear. Maturation of both male and female crayfish occurred during the fall of their third year at age 2+. Copulation of mature crayfish began during the first week of October in 1994 and 1995. In 1995, hatching began during the second week of April. The estimated mean days and thermal units required for egg incubation was 166 days and 2,208 degree-days, respectively. Mean pleopod fecundity during the incubation period was 105 ± 12 (mean ± 95% CI) eggs. Crayfish were captured as deep as 100 m, but 98% of the population was found at depths70 m. The peak relative abundance of crayfish occurred at 10-20 m. Diel activity of crayfish was primarily nocturnal and was skewed towards sunset. Eight age classes were identified from analyses of length-frequency distributions. The sex composition of crayfish appeared to be a 50:50 ratio and only deviated because of behavioral changes related to hatching. The mean density of crayfish, estimated from transects, in five habitat types ranged from 0.24 crayfish/m2 to 1.13 crayfish/rn2. The trappable population in Lake Billy Chinook was estimated to be 8,437,029 ± 2,252,332 crayfish. Total abundance, which included quadrat estimates for 0+ and I + crayfish, was estimated to be 35,940,145 ± 8,127,159. The mean molt increment of recaptured crayfish was 3.0 mm. The calculated population instantaneous mortality rate was Z = 0.67. Total estimated annual production and total biomass of crayfish was 21.16 g/m2 and 33.80 g/m2, respectively. The majority of tagged crayfish moved <500 m; however, 21% moved> 1,000 m in one year. Of the total volume of smallmouth bass Micropterus dolomieu stomachs that had food items, crayfish represented 95.3%. The crayfish population in Lake Billy Chinook had been commercially harvested since 1970. Harvest peaked in 1987 at 69,967 kg. There was a strong correlation between the number of commercial licenses and kg of crayfish harvested from 1981 to 1995. Management recommendations include decreasing the commercial fishing season by 2 months and requiring trap-set information to be recorded with harvest sales tickets.If managed wisely, P. leniusculus in Lake Billy Chinook could continue to support a sustainable fishery. ©Copyright by Scott D. Lewis 24 November 1997 All Rights Reserved Life History, Population Dynamics, and Management of Signal Crayfish in Lake Billy Chinook, Oregon. by Scott D. Lewis A THESIS submitted to Oregon State University in partial fulfillment of the requirements for the degree of Master of Science Presented 24 November 1997 Commencement June 1998 Master of Science thesis of Scott D. Lewis presented on 24 November 1997 APPROVED: Signature redacted for privacy. Mafor Professo reresenfiIg Fihene-Science Signature redacted for privacy. Fair of Department of Fishrie's and Wildlife Signature redacted forprivacy. Dean of Gr(uate School I understand that my thesis will become part of the permanent collection of Oregon State University libraries. My signature below authorizes release of my thesis to any reader upon request. Signature redacted for privacy. Scott D. Lewis, Author ACKNOWLEDGMENTS One of the greatest lessons that I learned over the course of this study was that it takes many more people to complete such a project than just the one author's name might imply.I would first like to thank my major professor, Howard Horton, for his guidance and patience over the duration of this study. Howard's years of experience enabled this study to run very smoothly without problems. When it seemed like things were running astray, a few hours in Howard's office would put me back on the track; although, our discussions usually ended up on Howard's hunting, fishing, or other life stories, which I enjoyed much more. Committee members Chris Langdon and Paul Murtaugh deserve thanks for finding time to review earlier drafts of the thesis and attend my study-related meetings.I want to thank Amy Stuart, Steve Thiesfeld, Terry Shrader, and Al Smith of the Oregon Department of Fish and Wildlife for help collecting smallmouth bass stomach data, providing historic crayfish data, and reviewing earlier drafts of the thesis. Colleen Fagan of the Confederated Tribes of Warm Springs Reservation was very helpful in the field at critical times and also reviewed an earlier draft of the thesis. My two research assistants, Darren Craig and Dave Lucei, were a great value in the field because of their tireless work habits.I enjoyed talking with local crayfishermen that fished Lake Billy Chinook during its heyday and trying to learn everything they knew about crayfish. Bob Brown was very helpful capturing tagged crayfish that were critical to the study. Columbia River Seafood provided the northern squawfish used for bait during the study at no cost. Many thanks go to the people involved at Portland General Electric (PGE) and Bonneville Power Administration for funding this study. Don Ratliff, the project biologist for PGE, helped with many parts of this study, and his help was greatly appreciated. Thanks to Even and Linda Thomas, I had a place to stay during both field seasons. During the many fall, winter, and spring trips to Lake Billy Chinook from Corvallis I could always count on my late grandma Theo Urbach for a warm place to sleep and plenty of food to eat. Most importantly, my wife Dianna who supported me through this long and difficult journey deserves more thanks than just words can convey. TABLE OF CONTENTS Page INTRODUCTION I Objectives 2 Literature Review 3 Life History 3 Population Dynamics 4 Management 7 Study Area 7 METHODS 11 General Methods 11 Life History 12 Reproduction 12 Pathogens and Parasites 14 Population Dynamics 15 Habitat 15 Age and Sex Composition 15 Density 16 Abundance 18 Growth and Mortality 19 Production and Biomass 21 Movements and Migrations 21 TABLE OF CONTENTS (Continued) Paqe Smalimouth Bass Predation 22 Management 23 Past Harvest and Management 23 Management Recommendations 23 RESULTS 24 Life History 24 Reproduction 24 Pathogens and Parasites 32 Population Dynamics 32 Habitat 32 Age and Sex Composition 36 Density 41 Abundance 44 Growth and Mortality 46 Production and Biomass 52 Movements and Migrations 52 Smailmouth Bass Predation 56 Management 58 Past Harvest and Management 58 Management Recommendations 67 TABLE OF CONTENTS (Continued) Paqe DISCUSSION 69 Life History 69 Reproduction 69 Pathogens and Parasites 71 Population Dynamics 72 Habitat 72 Age and Sex Composition 74 Density 75 Abundance 75 Growth and Mortality 77 Production and Biomass 78 Movements and Migrations 78 Smailmouth Bass Predation 79 Management 80 Past Harvest and Management 80 Management Recommendations 82 LITERATURE CITED 85 APPENDICES 94 LIST OF FIGURES Figure Page Location of Lake Billy Chinook in the Deschutes River Basin of Oregon and map of Lake Billy Chinook showing the Crooked River, Deschutes River, and Metolius River arms of the lake 9 Bathymetric map of Lake Billy Chinook. Shaded areas represent depths > 70 m 10 Percent mature male (n =263) and female (n = 502) crayfish per size class 25 Percent mature male and female crayfish plotted on probability scale. 26 Percent of total female catch for 1994 (n = 797) and 1995 (n = 1442) that had spermatophores or eggs attached from September to January 27 Percent of total female catch (n = 1,048) that had spermatophores, eggs, or 0+ age crayfish attached from 19 September 1994 to 12 May 1995 28 Mean number of pleopodal eggs, with 95% confidence intervals, for female crayfish captured with traps from November 1994 to March 1995 30 Linear regression of pleopodal eggs and post-orbital carapace length (mm) 31 Location of habitat types in Lake Billy Chinook 33 Depth distribution by 5-rn intervals of male and female crayfish captured from August 1994 to January 1996 35 Diel activity of crayfish expressed as mean number of crayfish, with 95% confidence intervals, captured per 10 traps per hour for 24 continuous hours (n = 1,971) 37 LIST OF FIGURES (Continued) Figure Page Length-frequency distributions of crayfish captured with traps from Boulder/Cobble, Sand/Silt, Mix, Draw-Down, and captured by hand from Draw-Down habitat 39 Monthly sex composition of crayfish catch from traps 40 Mean density of crayfish (No./m2), with 95% confidence intervals, from transect counts for Cliff (n = 4), Boulder/Cobble (n = 10), Sand/Silt (n = 10), Mix (n = 10), and Draw-Down (n = 10) habitat types 42 Mean density of crayfish, with 95% confidence intervals, at 5-rn depth intervals 43 Mean post-orbital carapace length (mm), derived from cohort length-frequency analysis, fitted with a von Bertalanify growth curve, with L. = 49, K = 0.38, and to = -0.5 47 Weight-length relation for male (n = 205) and female (n = 150) crayfish 48 Linear regression of post-molt post-orbital carapace length (mm) and pre-molt post-orbital carapace length (mm) for male (n = 7)