Dissertation - Open Access
Doctor of Philosophy (PhD)
Wildlife and Fisheries Science
David W. Willis
missouri river, reservoirs, sauger, sauger population, fish
Sauger Sander canadensis populations have experienced widespread declines across much of their range. Factors suspected to contribute to these declines include hybridization, exploitation, loss of spawning areas, and general habitat alterations associated with regulated rivers. Several sauger populations within the Missouri River basin are also experiencing similar declines, particularly in the headwaters of Montana, and the lower basin states of Nebraska and Missouri. However, sauger populations in many of the reservoirs in South Dakota (between Montana and the lower basin) have relatively stable populations. Given the paucity of information on factors influencing sauger population ecology in general, and Missouri River populations in particular, I studied several aspects of sauger population ecology in three Missouri River reservoirs to better understand factors influencing population structure. I focused on three primary research areas during the course of this study: 1) natural hybridization of sauger with walleye Sander vitreus, 2) sauger spawning habitat use in reservoirs, and 3) population dynamics of gizzard shad Dorosoma cepedianum, the primary prey fish for sauger in these systems. Results from this study will hopefully contribute to the understanding of sauger ecology and facilitate the advancement of conservation efforts. Walleye and sauger naturally hybridize in many populations, but factors influencing hybridization are not completely understood. I genetically identified and determined relative year-class strength for 1,454 sauger, walleye, and naturally produced hybrids from three Missouri River reservoirs (Lakes Sharpe, Francis Case, and Lewis and Clark) to examine patterns of hybridization, and to quantify factors influencing year class formation. Hybridization rates varied from 4% in Lakes Sharpe and Francis Case to 21% in Lewis and Clark Lake. Hybrids comprised several year classes in each system indicating that hybridization does not occur in erratic pulses, but rather at a consistent low-level recruitment rate. Hybridization was directionally biased toward walleye as 60- 72% of hybrids in each system were walleyes backcrossed with sauger genes. Yearclass strength of sauger, walleye, and hybrids varied among reservoirs and species within reservoirs. Neither year-class strength of hybrids nor walleye was correlated with that of sauger, indicating that dissimilar factors influence year-class strength among hybrids and pure parental walleye and sauger. As such, recruitment modeling was scaled at individual species and hybrids and within individual reservoirs. Because Lake Francis Case had a low sample size of cohorts to model (few individuals >age 5) this system was excluded from recruitment modeling. Factors affecting recruitment of hybrids in Lewis and Clark Lake and parentals in both Lakes Sharpe and Lewis and Clark shared the common positive influence of warmer water temperatures during fish early life history, but recruitment differed among species and systems with regard to the effect of flow. Increased flow, either from mainstem cumulative discharge (hybrids) or tributary inputs (parentals), was negatively associated with year-class strength in my models for Lewis and Clark Lake, whereas tributary inputs and discharge were not well supported in models for sauger in Lake Sharpe (although tributary input warrants further investigation for walleye). The effect of flow on recruitment of sauger and walleye in Lewis and Clark Lake was confounded by an interaction with temperature. Tributary inputs negatively affected recruitment of sauger and walleye when water temperatures were reduced, but the effect of tributary input was negated during warmer years. Thus, these models suggest that higher than average recruitment can be expected during years with warmer spring/early summer water temperatures in Lakes Sharpe and Francis Case, and during years when flow (either from mainstem discharge for hybrids, or tributary inputs for sauger and walleye) are reduced in Lewis and Clark Lake.
Library of Congress Subject Headings
Sauger -- South Dakota -- Sharpe, Lake
Sauger -- South Dakota -- Francis Case, Lake
Sauger -- Lewis and Clark Lake (S.D. and Neb.)
Sauger -- Ecology -- Missouri River Watershed
Number of Pages
South Dakota State University
Copyright © 2006 Brian D. S. Graeb. All rights reserved.
Graeb, Brian D. S., "Sauger Population Ecology in Three Missouri River Mainstem Reservoirs" (2006). Electronic Theses and Dissertations. 438.