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Muskellunge Esox masquinongyare 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 artedias 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 flavescentCPUE 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 commersoniiwere 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.

Fish stocking, often from multiple source populations, is a common management practice frequently conducted without the means or effort to determine the reproductive contributions of stocked fish. Historically, the Minnesota Department of Natural Resources (MNDNR) has stocked four strains of muskellunge Esox masquinongy, but the contribution of these strains to current populations was unknown. Two strains came from Minnesota lakes, Shoepack Lake and Leech Lake, and the other strains came from Wisconsin and Iowa hatcheries and were of uncertain origin. The MNDNR discontinued stocking the Shoepack strain in the 1980s when that strain displayed poor growth in stocked waters. Managers were concerned that ancestry from this strain might be limiting the genetic potential for muskellunge to attain trophy size in stocked populations. Using 13 microsatellite DNA markers, we determined the ancestry of muskellunge in 10 supplemented native populations and 10 introduced populations. The ancestry from each of the four stocked strains of muskellunge was detected in some populations, but the level of ancestry was unrelated to the amount of stocking of a strain. Ancestry from native populations persisted in six of the supplemented populations despite years of stocking. The potential effects of Shoepack strain ancestry on fish size were limited in most lakes because of its low persistence. All stocked strains reproduced in at least some of the lakes, but some lakes had no evidence of reproduction by any stocked strain. Our results will help MNDNR manage genetic diversity among muskellunge populations and direct efforts toward appropriate actions to improve size structure. This study reinforces how genetic data are often useful for evaluating ancestry in stocked fish populations, whereas stocking histories may be poor indicators of current genetic composition.

The popularity of sportfishing for muskellunge Esox masquinongyin Minnesota has increased substantially during the last 20 years and has resulted in a call for creating more fishing opportunities. As new waters are considered for muskellunge management, some anglers have expressed concern over the effects on other popular game fish species of adding a top-level predator. We evaluated the responses of seven fish species to muskellunge by comparing gill-net and/or trap-net catch per unit effort (CPUE) before and after muskellunge were stocked in 41 Minnesota lakes composed of 12 lake-classes. The species examined were northern pike Esox lucius, walleye Sander vitreus, yellow perch Perca flavescens, bluegill Lepomis macrochirus, black crappie Pomoxis nigromaculatus, white sucker Catostomus commersonii, and cisco Coregonus artedi. We found no significant decreases among the lakes in the mean CPUE of any species after muskellunge stocking, either for the stocked lakes as a whole or within lake-classes. There was a significant increase in the mean CPUE for bluegills over the entire group of lakes and within lake-class 24 in addition to an increase in the mean CPUE for black crappies sampled by gill nets in lake-class 25. Nevertheless, there was large variability in the changes in CPUE among lakes, and several individual lakes had significant changes in mean CPUE for some species following muskellunge stocking. The trend in CPUE increased for yellow perch and declined for white suckers over the entire group of lakes after muskellunge stocking. Because Minnesota follows established, biologically based guidelines for selecting new muskellunge lakes, the study lakes were not chosen at random and therefore the study conclusions most appropriately apply to lakes chosen in this manner. The lack of consistent negative changes in CPUE after stocking suggests that these fish species have generally coexisted well with muskellunge in these lakes at the densities that have resulted from stocking. Received June 21, 2010; accepted October 28, 2011

The effects of stocked fish on native populations of the same species are poorly understood. During the 1960s-1980s, the Minnesota Department of Natural Resources (MNDNR) stocked muskellunge Esox masquinongyderived from Shoepack Lake in the Hudson Bay drainage of northern Minnesota into Moose Lake in the Upper Mississippi River drainage. In the mid-1980s, the MNDNR recognized that stocked Shoepack Lake-strain fish (hereafter, Shoepack strain) were not attaining large sizes, and sources were switched statewide; subsequently, muskellunge from a Wisconsin hatchery were stocked once into Moose Lake. We used 14 microsatellite DNA markers to estimate the genetic contribution by each source population to muskellunge sampled in four different years from 1981 to 2004, and we evaluated the effects of Shoepack-strain ancestry on fish size. Two samples in the 1980s had mostly fish with a single ancestry; thus, these fish were probably Shoepack-strain fish stocked a few years earlier or native fish. By 2004, when most fish would have been naturally produced in the lake, contributions from all three source populations were detected, including admixed individuals from crosses among all ancestral sources. The estimated ancestry by source was 52% native Moose Lake ancestry, 29% Wisconsin strain, and 19% Shoepack strain, with 24% of the individuals having pure Moose Lake ancestry. Fish without Shoepack-strain ancestry had a greater median length than did those with Shoepack-strain ancestry and had a greater proportion of legal-sized individuals (total length = 1,016 mm) in the population. In contrast, Moose Lake and Wisconsin-strain descendents were common among all sizes of fish. Management options include doing nothing, accepting that extensive introgression has already occurred, or manipulating the population by either stocking to dilute Shoepack-strain ancestry or genetic screening to purge the population of Shoepack-strain ancestry.

Predation by walleye Stizostedion vitreumand sauger S. canadenseon paddlefish Polyodon spathulawas noted in Lake Sakakawea, North Dakota. Percid predation on paddlefish was detected at two of three sampling stations in September and at one sampling station in October. In October, 73% of the percids with identifiable food contained at least one paddlefish. Total length of ingested paddlefish ranged from 36 to 52% of percid total lengths. When designing stocking programs, fisheries managers should consider percid predation as a potential source of mortality of stocked paddlefish.