Analysis of Grass Carp Dynamics to Optimize Hydrilla Control in an Appalachian Reservoir By Matthew A. Weberg Thesis submitted to the graduate faculty of Virginia Polytechnic Institute and State University in partial fulfillment of the requirements for the degree of Master of Science in Fisheries and Wildlife Approvals: Brian Murphy, Committee Co-chair Andrew Rypel, Committee Co-Chair Leandro Costello, Committee Member John Copeland, Committee Member October 7th, 2013 Julian Cheatham Hall Room 136B, Blacksburg, Virginia Keywords: biological control, population dynamics, radio telemetry, grass carp Analysis of Grass Carp Dynamics to Optimize Hydrilla Control in an Appalachian Reservoir Matthew A. Weberg Abstract The primary objectives of this study were: 1) to evaluate the movement patterns, habitat use, and survival of triploid grass carp Ctenopharyngodon idella stocked to control hydrilla Hydrilla verticillata in a riverine reservoir (Claytor Lake, Virginia), 2) to examine grass carp population dynamics and hydrilla growth dynamics in Claytor Lake to guide long-term management efforts, and 3) to describe the aquatic plant community in the New River upstream of Claytor Lake to assess the potential for alterations due to potential grass carp herbivory. Only 3% of radio-tagged grass migrated out of Claytor Lake during the 2-year study. Grass carp movement patterns were significantly correlated with temperature-, weather-, and habitat-related variables. Grass carp selected specific cove, shoal and tributary habitats colonized by hydrilla. First-year survival of grass carp was 44% in 2011, and 25% in 2012. Grass carp growth rates were rapid in 2011, but declined in 2012 concurrent with significant reductions in hydrilla abundance. Based on grass carp population dynamics observed in Claytor Lake, our stocking model predicted that hydrilla could be controlled through 2030 by a grass carp standing stock of 5-6 metric tons. We documented 12 plant species in the New River upstream of Claytor Lake, 9 of which are preferred plants for grass carp suggesting that the plant community could be altered if migration rates increase. Grass carp can be effective for managing hydrilla in riverine reservoirs; however, continued monitoring of grass carp population dynamics, migration rates, and vegetation abundance could facilitate greater precision in management efforts. Acknowledgements I thank the Virginia Department of Game and Inland Fisheries (VDGIF), Virginia Tech Department of Fish and Wildlife Conservation, Pulaski County, and the Sportfish Restoration Program for funding my research. Additionally, I thank Claytor Lake State Park, Appalachian Power, Friends of Claytor Lake, and the Claytor Lake Technical Advisory for their efforts throughout this project. I thank my committee members, Brian Murphy, Andrew Rypel, John Copeland, and Leandro Castello for their faith in me as a fisheries scientist, and also for their guidance in all facets of my research. I am also grateful for the involvement of Bill Kittrell, George Palmer, and many other fisheries staff members from VDGIF that donated precious hours assisting with planning, stocking, and radio-tagging grass carp used in my study. I thank my technicians, Scott Riley and Preston Chrisman, for their willingness to go the extra mile to ensure my research was successful, and Robert Humston for guidance as I stepped into the realm of ecological modeling. I thank my loved ones for sticking with me through all the struggles, providing hope when it was needed most, and being there to celebrate my successes. Finally, I thank all of my wonderful volunteers that were an essential component of this research including: Amanda Graumann, Ben Dickinson, Bonnie Meyers, Nate Adkins, John Woodward, Jason Emmel, Joey Schmitt, Bill Bond, students in the 2012 and 2013 Fish Management course, and all other graduate students for their encouragement and companionship. iii Table of Contents Chapter 1: Introduction Introduction………………………………………………………………………………..1 Study Site…………………………………………………………………………….......10 Study Objectives…………………………………………………………………………15 Literature Cited…………………………………………………………………………..15 Chapter 2: Analysis of grass carp movement patterns, habitat use, and survival in an Appalachian reservoir Abstract…………………………………………………………………………………..26 Introduction………………………………………………………………………………27 Methods…………………………………………………………………………………..29 Results……………………………………………………………………………………36 Discussion……………………………………………………………………………......45 Literature Cited…………………………………………………………………………..52 Chapter 3: Examination of grass carp and hydrilla dynamics to guide future management in an Appalachian reservoir Abstract…………………………………………………………………………………..60 Introduction………………………………………………………………………………61 Methods…………………………………………………………………………………..64 Results……………………………………………………………………………………71 Discussion……………………………………………………………………………......79 Literature Cited…………………………………………………………………………..87 Chapter 4: A survey of the aquatic plant community of the New River upstream of Claytor Lake Abstract…………………………………………………………………………………..95 Introduction………………………………………………………………………………96 Methods…………………………………………………………………………………..97 Results……………………………………………………………………………………99 iv Discussion……………………………………………………………………………....102 Literature Cited…………………………………………………………………………106 Chapter 5: Conclusions Summary………………………………………………………………………………..113 List of Figures Figure 1.1 Map of Claytor Lake a 1,876-ha mainstream impoundment of the New River located in Pulaski County, Virginia, USA……………………………………………………………….11 Figure 2.1. Map of Claytor Lake, Pulaski County, Virginia, USA including hydrilla coverage documented in 2010, and grass carp stocking locations Claytor Lake State Park (CLSP), Lowman’s Ferry Bridge (LMFB), and Old Hurst Rd (OHRD) used in 2011…………………..31 Figure 2.2. Average monthly movement (AMM, ±SE) observed for two stocking cohorts of radio-tagged grass carp in Claytor Lake between May-11 and April-13…………………….......38 Figure 2.3. Post-stocking dispersal of the 2011 (A) and 2012 (B) stocking cohorts released into Claytor Lake. Generally, locations in the SW quadrant indicate upstream movement, locations in the NE quadrant indicate downstream movement, and locations in the NW quadrant indicate movement into major tributaries…………………………………………………………………40 Figure 2.4. Habitat classification map for Claytor Lake, percent of total habitat represented by each habitat type, and the number of radio-tagged grass carp locations (percent of total locations in parentheses) observed for each habitat type, by stocking cohort……………………………..43 v Figure 2.5. Estimated first-year survival of grass carp stocked in Claytor Lake in 2011, and 2012 based on time-dependent survival models generated from the known-fates analysis in program MARK. Radio-tagged grass carp that did not survive beyond one month post-release were removed from the analysis due to the likelihood that mortality was due to surgery-related complications, or tag loss………………………………………………………………………..45 Figure 3.1. Map of Claytor Lake, Pulaski County, Virginia along with hydrilla coverage identified during a fall 2010 survey……………………………………………………………..65 Figure 3.2. Conceptual model of stocked grass carp and hydrilla dynamics used to simulate hydrilla control by grass carp in Claytor Lake. Boxes in the submodels represent stocks (i.e. total hydrilla biomass, or number of grass carp), the double-line arrows represent flows in or out of the respective systems, and single-line arrows are convertors………………………………..69 Figure 3.3. Annual peak hydrilla biomass levels predicted by the hydrilla submodel, compared with hydrilla coverage survey estimates converted to biomass assuming a hydrilla density of 1.25 kg m-2. Overall the model accurately portrayed hydrilla expansion between 2003 and 2010, and predicts that peak hydrilla biomass levels will reach carrying capacity by 2022 in Claytor Lake without grass carp management………………………………………………………………….76 Figure 3.4. Predicted peak hydrilla and grass carp biomass in Claytor Lake for 2011-2030 under grass carp dynamics used in Mc. The model predicts that a stocking rate of approximately 320 kg vi of grass carp annually is required to maintain peak hydrilla biomass at approximately 500 metric tons, or 40 ha of full hydrilla coverage………………………………………………………….78 Figure 4.1.—Surveyed section of the Upper New River including locations of drift net sampling sites between Buck Dam near Ivanhoe, Virginia, and the start of Claytor Lake near Allisonia, Virginia…………………………………………………………………………………………..98 Figure 4.2. Total plant biomass (g) collected in drift-net samples taken in July 2012 at eight sites in the New River between Buck Dam and Allisonia. The dashed line indicates the furthest point upstream of Claytor Lake we documented grass carp during a concurrent telemetry study (Chapter 2)……………………………………………………………………………………..101 List of Tables Table 1.1 Comparison of selected United States waterbodies where grass carp have been stocked to control hydrilla infestations…………………………………………………………………...12 Table 1.2 Characteristics of submerged aquatic vegetation found within the Claytor Lake project during 2007 survey (Source: Appalachian Power 2008)………………………………………...13 Table 2.1. Demographics of grass carp stocked into Claytor Lake in May 2011 and April 2012 including grass carp used in a telemetry study (R), and grass carp stocked for biological control of hydrilla (B)……………………………………………………………………………………38 vii Table 2.2. PCA loading matrix and percent contribution (in parentheses) for 14 abiotic and biotic variables used to characterize observed