The popularity of sportfishing for muskellunge Esox masquinongy in 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.
Ecological impacts of fish introductions: Evaluating the risk
Ecological impacts of fish introductions: Evaluating the risk
Interactions between walleye and four fish species with implications for walleye stocking
We used a number of different data sets and four criteria to evaluate evidence of competition and predation between walleye Sander vitreus and northern pike Esox lucius, muskellunge E. masquinongy, smallmouth bass Micropterus dolomieu, and largemouth bass M. salmoides in northern Wisconsin lakes. The four criteria were as follows: (1) indices of population abundance were inversely related, (2) two species had shared resources or one species preyed on the other, (3) competition or predation was strong enough to produce a measurable effect, and (4) experimental manipulations produced results consistent with the hypothesis of competition or predation. Using these criteria, we identified which species interact most strongly with walleyes, determined the most likely mechanism for interaction (predation, competition, or both), and characterized the effects of walleye stocking on these species. Largemouth bass was the only species that strongly interacted with walleyes: (1) indices of largemouth bass and walleye population abundance were inversely related in lakes with self-sustaining walleye populations; (2) the diet of largemouth bass included juvenile walleyes; (3) walleye growth was positively related to indices of largemouth bass abundance; and (4) survival of stocked walleyes was negatively related to indices of largemouth bass abundance, and indices of largemouth bass abundances increased as an index of walleye stocking intensity increased. A bioenergetics analysis of one lake that was stocked with 39,300 juvenile walleyes, but also has some natural reproduction of walleyes, suggested that the largemouth bass population could consume up to 82,500 juvenile walleyes per year. Our findings suggest that largemouth bass interact strongly with walleyes through predation, that they can limit the survival of stocked walleyes, and that walleye stocking can result in increased largemouth bass populations. Therefore, management goals seeking to simultaneously maximize largemouth bass and walleye populations may be unrealistic.
Egg distribution and spawning habitat of northern pike and muskellunge in a St. Lawrence River marsh
Coexistence of northern pike Esox lucius and muskellunge Esox masquinongy in the Niagara and St. Lawrence rivers has been hypothesized to depend on segregation during spawning. However, large overlap in the use of spawning areas by these two species occurs in the Thousand Islands section of the upper St. Lawrence River. In this study, egg collections in Point Marguerite Marsh in the upper river revealed a partial temporal and spatial overlap in egg deposition by northern pike and muskellunge. Northern pike began spawning earlier but overlapped with muskellunge spawning for 2 weeks, May 13–27. Northern pike eggs were collected over a larger area than muskellunge eggs and at all locations where muskellunge eggs were collected. Both species deposited eggs over three dominant genera of vegetation: pondweeds Potamogeton, duckweeds Lemna, and stonewort Chara. Northern pike spawned over a wider range of water depths (0.5–2.6 m) than muskellunge (0.8–1.5 m) and selected habitats with denser, taller vegetative cover. The temporal and spatial overlap of northern pike and muskellunge egg deposition suggests that mechanisms other than spawning segregation permit these two species to coexist in the St. Lawrence River.
Potential effects of spawning habitat changes on the segregation of northern pike and muskellunge in the Upper St. Lawrence River
Changes in spawning habitat of northern pike (Esox lucius) may affect their segregation from and coexistence with the closely related muskellunge (E. masquinongy). We estimated the areal coverage of robust and shallow emergent vegetation in three shared-spawning bays in the Upper St. Lawrence River from aerial photographs taken from 1948 to 2003. Robust emergent vegetation (e.g., cattail) increased in coverage by 155–241% while shallow emergents (sedges) decreased by 46–96%. The loss of sedges, an important northern pike-spawning habitat, may facilitate greater spawning overlap in offshore-submersed aquatic vegetation within bay habitats used by muskellunge. Development rates and characteristics of northern pike and muskellunge eggs and larvae were compared to better understand the implications of greater spawning overlap. Northern pike eggs developed faster than muskellunge eggs at temperatures of 4.7–19°C, and adhesive eggs and the presence of adhesive papillae were present in both species. Equations were used to predict degree-day requirements for hatching and swim-up in three habitats (shallow emergents, bay, and offshore shoal) along a temperature gradient. Northern pike required more estimated degree days to reach hatching in bay and offshore shoal habitat relative to shallow emergent habitat due to cooler temperatures. Significant spawning overlap is known to occur within bay habitats, but poor success of northern pike in deep bay habitats and overall reductions in abundance are hypothesized to currently buffer muskellunge from potential negative interactions between these species.
Using movements and diet analysis to assess effects of introduced muskellunge on Atlantic salmon in the St. John River, New Brunswick
The muskellunge was introduced in the Saint John River system from stockings in a headwater lake in the 1970s. They have migrated down the system as far as the river’s first dam, Mactaquac Hydroelectric Facility, at Fredericton and appear to have established several reproducing populations along the river. This exotic invader represents a potential threat to the severely depleted Atlantic salmon stocks in the river. We radio-tracked muskellunge over a 2- year period in the middle reaches. Home ranges extended to ~100 km in both riverine and lacustrine areas, including 78% of individuals translocated upstream of the dam making their way back through the dam successfully. Downstream of the dam, home ranges were <25 km. No spawning areas were detected. An isotope analyses of diet indicated that the large sub-adults and adults had established the greatest proportion of their biomass in a more 15N depleted environment typical of areas farther upstream. Isotope mixing models could not accurately determine the proportion of Atlantic salmon smolts that may have been consumed by muskellunge, but anadromous salmon had £7% probabilities of being in the diet. A bioenergetics model suggested £5% of the annual food intake by muskellunge occurs during the smolt out-migration period. For the Saint John River, the impacts of growing numbers of muskellunge are multi-faceted creating a complex management challenge. Muskellunge appear to minimally increase predation risk for Atlantic salmon smolts while their increasing numbers are creating a growing recreational fishery and potential threat to the native fish community and ecosystem.