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Thesis - University Access Only
Master of Science (MS)
Wildlife and Fisheries Science
David W. Willis
Gizzard shad Dorosoma cepedianum were introduced into Angostura, Orman, and Shadehill reservoirs during the 1990s to potentially provide increased prey resources for walleye Sander vitreus. The objectives of this study were to assess gizzard shad reproductive biology and determine the extent to which gizzard shad contribute to the walleye prey base at this northern latitude. Adult gizzard shad (N = 100) were collected by electrofishing during spring 2004 in Angostura Reservoir. All adult gizzard shad were 338 mm total length, or larger, and sagittal otoliths indicated that recruitment to the adult stage was erratic (three cohorts sampled) with age-3 individuals comprising over 80 percent of the sample. I expected winter severity to be the primary factor influencing overwinter survival of age-0 gizzard shad; however, correlations between gizzard shad year-class strength and my indices of winter severity and winter duration revealed no evidence that winter harshness influenced gizzard shad recruitment to the adult stage. Rather, I suggest that age-0 gizzard shad size attained by the onset of winter (influenced by age-0 gizzard shad abundance and summer temperatures) and winter temperatures likely interact to regulate overwinter survival of age-0 gizzard shad in Angostura Reservoir. Larval gizzard shad abundance (number/100 m3) estimated using surface trawls was substantially higher in Orman Reservoir during both years compared to Angostura and Shadehill reservoirs. Larval gizzard shad densities in Orman Reservoir were within the range of larval gizzard shad densities measured in other U.S. locations, while Angostura and Shadehill reservoirs were both lower. Mean daily growth rate (estimated by enumerating daily rings on sagittal otoliths) of juvenile gizzard shad ranged from 0.73 to 1.50 mm/d among the three populations during both years and was significantly lower during both years in Orman Reservoir, which exhibited the highest abundance of age-0 shad. Correlations between mean daily growth rate of age-0 gizzard shad and juvenile gizzard shad abundance (i.e., CPUE determined from shoreline electrofishing) were negative. Peak gizzard shad hatch date occurred during early to mid-June in all three reservoirs during both years and was unimodally distributed except for Shadehill Reservoir during 2005. Earlier-hatched gizzard shad attained larger sizes by time of capture in all three reservoirs during both 2004 and 2005. By the end of July, a broader range in total length of juvenile gizzard shad was present in Shadehill and Angostura reservoirs compared to Orman Reservoir. The largest age-0 gizzard shad collected during mid-September in Orman Reservoir was 85 mm; whereas, 165-mm age-0 shad were collected in Shadehill Reservoir at that same time. Based on observed age-0 gizzard shad abundance, growth rate, and length-frequency distributions in western South Dakota reservoirs, I suggest that a density-dependent threshold exists where age-0 shad growth slows. Assuming recruitment of age-0 gizzard shad to age-1 is size-dependent, then earlier-hatched shad in lower density populations likely have the best chance of surviving extended South Dakota winters. Walleye food habits were examined monthly from April through September during 2004 in Angostura Reservoir and seasonally (i.e., May, July, and September) during 2005 in Orman and Shadehill reservoirs. Generally, macroinvertebrates were primarily consumed in all populations from spring to mid-summer and the percentage of empty walleye stomachs was generally highest during that time. Age-0 gizzard shad were not observed in walleye diets until late July; however, during that time frame through mid-September, walleye food habits were dominated by age-0 gizzard shad in all three reservoirs. The percentage of empty walleye stomachs was also lowest during that period indicating that when age-0 gizzard shad were available walleye utilized them extensively. Bioenergetics modeling indicated that mean walleye weight decreased among cohorts until age-0 gizzard shad were consumed and that walleye growth was directly affected by age-0 gizzard shad consumption during 2004 in Angostura Reservoir. Percentage of maximum consumption values indicated that all walleye cohorts were feeding more frequently following age-0 gizzard shad availability. This corroborates the decrease in percentage of empty walleye stomachs during August and September and indicates that prey resources were likely limited during spring through mid-summer in Angostura Reservoir. These results indicate that the importance of age-0 gizzard shad availability is high for walleye in all three reservoirs.
Library of Congress Subject Headings
Gizzard shad -- South Dakota
Gizzard shad -- South Dakota -- Reproduction
Walleye (Fish) -- Food -- South Dakota
Includes bibliographical references (page 110-122)
Number of Pages
South Dakota State University
Copyright © 2005 Matthew J. Ward. All rights reserved.
Ward, Matthew J., "Gizzard Shad Reproductive Biology and Predator-Prey Relations with Walleyes in Western South Dakota Reservoirs" (2005). Theses and Dissertations. 595.