Utility of Walleyes and Saugeyes as Secondary Predators in Small South Dakota Impoundments

Walleye Stizostedion vitreum and saugeye (walleye x sauger S. canadense) fingerlings were concurrently stocked at equal densities into five small impoundments in 1997, 1988, and 1999 to evaluate relative survival, growth and their ability to restructure existing panfish communities. Prior to stocking, fish were differentially marked on the right or left side with freeze brands or with 700 ppm oxytetracycline hydrochloride (OTC) to allow accurate identification of each fish as a walleye (fry mark) or a saugeye (fingerling mark). Spring and fall night electrofishing was used to sample the stocked percids, as well as potential competing species such as largemouth bass Micropterus salmoides and northern pike Esox lucius. Differences in relative survival (indexed as catch per unit effort [CPUE] from night electrofishing) and growth (mean total length and relative growth) between walleyes and saugeyes were compared within and among water bodies. Visceral-somatic index (VSI), liversomatic index (LSI) and mesenteric fat index (MFI) were calculated for both species to further compare fish condition. Changes in panfish communities (indexed as trap net CPUE, proportional stock density [PSD], relative weight [Wr] and incremental growth) were assessed throughout the study. The 1997 year class of walleyes exhibited better survival than saugeyes in Bode Pond and Jones Lake. Low sample sizes and no significant differences in survival were observed in Hanson, Iroquois or Hayes Lake populations. The 1998 cohort of walleyes had significantly higher survival than saugeyes in Hanson Lake during fall 1999 and spring 2000. Saugeyes survived better than walleyes in Bode Pond during fall 2000. In all other lakes survival of both percids was very low. For the 1999 cohorts, relative survival of walleyes was significantly higher in Lake Iroquois during spring 2000 and in Hanson Lake during fall 2000. Saugeye CPUE in Bode Pond during fall 2000 was significantly greater than the walleye CPUE; however, both catch rates were very low. Survival of both percids in Hayes and Jones Lakes was very low, likely due to competition with and predation by abundant largemouth bass populations. The lack of percid survival in Lake Iroquois appeared linked to summer mortality. Overall, survival of stocked walleyes and saugeyes was low in all study impoundments, with the exception of the introductory stocking in Bode Pond, which produced a high-density percid fishery. Relative growth of walleyes and saugeyes was inconsistent among waters, but was generally similar within each lake for the 1997 year class. Where sympatric populations developed, percid growth always favored walleyes for the 1998 and 1999 year classes. Percid condition was also variable among lakes, but was usually similar within each lake for all year classes. Overall, neither percid demonstrated a substantial advantage in performance in small South Dakota impoundments. Panfish community effects were evaluated in Jones and Hanson lakes. In Jones Lake, the only substantial panfish community effect that may have been caused by stocked percids was the reduction of yellow perch Perea flavescens abundance and the substantial increase in the bluegill Leoomis macrochirus abundance. Such a pronounced shift was most likely a result of selective predation for yellow perch by walleye and saugeye. However, an increase in the largemouth bass population during this study reduced the ability to attribute changes in the panfish community directly to stocked percids. In Hanson Lake, competing predator populations remained low throughout the study, indicating that observed changes in the panfish community were likely a result of predation by the stocked percids. The PSD of all panfish species showed significant improvements between 1997 (pre-stocking) and 2000 (post-stocking). The incremental growth rates of bluegills and black crappies Pomoxis nigromaculatus also exhibited significant increases between 1997 and 2000. These trends indicate that the stocked percids, through increased predation, were able to improve the size structure and growth of panfish in Hanson Lake