Are Muskellunge Affecting Fish Communities in Waters Where They Have Been Introduced? A Re‐examination of Minnesota’s Stocked Muskellunge Waters

Abstract

Muskellunge Esox masquinongy are large piscivores stocked into numerous lakes in North America, but the potential effects of these stockings remains poorly understood. To investigate potential fish community changes associated with Muskellunge stocking, we contrasted catch per unit effort (CPUE) for seven fish species commonly found in Minnesota, along with mean weight for two predator species, before and after Muskellunge introduction in 36 lakes with that of paired reference lakes. Because of the known importance of Cisco Coregonus artedi as prey for Muskellunge, we also examined these data by separating the lakes into those with and without Cisco. Across all 36 lakes, we observed several significant differences between stocked and reference lakes. Yellow Perch Perca flavescent CPUE in gill nets were significantly higher after Muskellunge were introduced, as was mean weight for Northern Pike Esox lucius. Gill‐net CPUE for Northern Pike and White Sucker Catostomus commersonii were both lower following Muskellunge introduction. When subsets of lakes with and without Cisco were considered, results for the 21 lakes without Cisco were similar to the results of the entire set of lakes. In the 15 lakes with Cisco, the only significant result was lower Northern Pike CPUE after Muskellunge stocking. Our results are evidence that the introduction and management of Muskellunge in these lakes has not adversely affected game fish populations.

Diet Patterns and Niche Overlap of Muskellunge and Co‐Occurring Piscivores in Minnesota Lakes

“…To our knowledge, this study is the first to examine the diet patterns of sympatric piscivores in lakes with and without Muskellunge. The consistent diet patterns observed suggest no effects-either direct or indirect-of Muskellunge on feeding patterns of the species examined and provide further evidence that Muskellunge do not negatively affect co-occurring fish populations (Inskip and Magnuson 1983;Fayram et al 2005;Knapp et al 2012Knapp et al , 2021.…”

“…Additionally, the CPUE of White Sucker decreased following Muskellunge stocking in 21 lakes without Cisco while no change was documented in 15 lakes where Cisco were present, which could indicate that Muskellunge prefer Cisco to White Sucker as prey when both species are available (Knapp et al. 2021). Those results support current guidance for new Muskellunge introductions in Minnesota, which indicates that lakes with healthy coregonid populations should be prioritized because these prey populations likely serve as primary diet items (MN DNR 2008).…”

Using stable isotope data to quantify niche overlap and diets of muskellunge, northern pike and walleye in a deep Minnesota lake

“…Considering that muskellunge occur at low density in most lakes and that these lakes typically have diverse, abundant prey fish populations, muskellunge influences on resident fish populations should be minimal (Knapp et al., 2012). Subsequent follow‐up of the Knapp et al., (2012) study with more data and additional control lakes also showed no deleterious effects of muskellunge on other sport fish populations and provided evidence of beneficial changes to size structure in northern pike populations (Knapp et al., 2021). Based on the stable isotope data from Elk Lake, it does not appear that walleye or northern pike were an important diet component for muskellunge because muskellunge δ 15 N signatures were not elevated relative to walleye and northern pike, and δ 13 C signatures were also too depleted in muskellunge to indicate consumption of northern pike.…”

Cisco population characteristics in Wisconsin lakes in relation to lake‐ and landscape‐level factors

“…Our study and many previous assessments (e.g., Jacobson et al 2008;Honsey et al 2016) have focused on lake-and landscape-level physiochemical (i.e., abiotic) predictor variables; however, biotic factors, such as predation or competition, could also influence abundance and growth (e.g., Larkin 1956;Carpenter et al 1985). Cisco can serve as prey for fishes including Lake Trout (Matuszek et al 1990;Parks and Rypel 2018), Rainbow Smelt Osmerus mordax (during the larval stage; Hrabik et al 1998;Sharma et al 2011), Muskellunge (Bozek et al 1999;Knapp et al 2021;Herwig et al 2022), Northern Pike (Jacobson 1992;Kennedy et al 2018), and Walleye (Henderson et al 2004;Kaufman et al 2009). However, pelagic-oriented piscivores such as Lake Trout rarely occur in inland Cisco lakes in Wisconsin, and several studies have reported that the occurrence of Cisco in diets of littoral-oriented predators is generally low (<20%; Bozek et al 1999;Krueger and Hrabik 2005;Kaufman et al 2009).…”