Purpose :

1. Stocking Density, Walleye Survival, and Zooplankton Communities at Baldhill National Fish Hatchery Amy Doll 1, Casey Williams 1, Kurt Eversman 2, David Demuth3; 1Department of Science, Valley City State University, Valley City, ND 58072; 2US Fish and Wildlife Service Valley City National Fish Hatchery, Valley City, ND 58072, 3 Great Plains STEM Education and Research Center, Valley City State University, Valley City, ND 58072 Purpose: Results: • Walleye percent survivorship was significantly higher (P < 0.05) when stocked at 200,000 FPSA (mean = 47.5%, SD =0.7) than 300,000 FPSA (mean = 25.5%, SD =6.4; Figure 2). • Although not statistically significant (P >0.05), walleye survivorship was higher when stocked at 200,000 FPSA than when stocked at 250,000 FPSA (mean = 33%, SD = 1.4). • Similar trends in zooplankton abundance across ponds suggests zooplankton abundance is not a limiting factor between different stocking rates (Figure 3). • This study was conducted to examine juvenile walleye Sander vitreus fry survivorship at three stocking densities in ponds at Baldhill National Fish Hatchery. • Walleye survival rates were correlated with temporal patterns in zooplankton populations to examine possible interspecific regulation of walleye abundance and survival. Methods: • Walleye • Fry were stocked in six ponds (Figure 1) at three stocking rates on June 3, 2013 • 200,000 fish/surface acre (FPSA) – Ponds 2 and 5 • 250,000 fish/surface acre – Ponds 6 and 9 • 300,000 fish/surface acre – Ponds 13 and 14 • Harvested between June 24th and June 26th • Percent survival of walleye stocking densities were arcsine transformed and analyzed with 1 Factor Analysis of Variance (ANOVA; α = 0.05). Tukey’s test (α = 0.05) were used for pairwise comparisons. • Ponds were normally fertilized twice a week. • Zooplankton • Sampled on Mondays and Thursdays during June. • Split into manageable sample size using a Folsom plankton splitter • Counted and identified using a Ward Counting Wheel. • Categorized into five groups: rotifers, cyclopoids, calanoids, nauplii, and cladocerans Conclusion: • Compared to higher stocking rates, stocking walleye fry at 200,000 fish per surface acre results in the highest survivorship; thus, the lower stocking density should be used to maximize walleye production at Baldhill National Fish Hatchery (Figure 4). • Current fertilization rates appear to promote adequate zooplankton communities to support walleye production at Baldhill National Fish Hatchery. 1 Figure 2. Percent survivorship for three stocking rates of walleye fry at Baldhill National Fish Hatchery. Letter designations (A, B) represent statistical significance (α = 0.05) between stocking rates. 2 4 3 5 8 6 9 12 7 10 13 15 11 17 14 16 18 19 20 } 200,000 FPSA Figure 4. Mean number of fish produced per surface acre for three stocking densities at Baldhill National Fish Hatchery. } 250,000 FPSA } 300,000 FPSA Figure 3. Temporal plankton density in Baldhill National Fish Hatchery ponds stocked with walleye fry at three stocking densities. Figure 1. Aerial view of Baldhill National Fish Hatchery