The purpose of this study was to identify spawning habitat, determine home ranges, and examine movement patterns for a naturally reproducing population of Great Lakes muskellunge in the lower Antrim County chain of lakes, Michigan. Muskellunge spawning sites were identified by tracking of implanted muskellunge using a directional hydrophone and by nighttime spotlight surveys. All spawning fish tagged in Torch or Clam Lake spawned in Clam Lake, while most spawning fish tagged in Elk or Skegemog Lake spawned in the Torch River; one appeared to spawn in Lake Skegemog. Of the 32 potential spawning sites, 28 (87.5 %) contained submerged aquatic vegetation as the dominant habitat type, while the remaining 4 sites were divided equally between woody debris (6.25 %) and bare substrate. All but one implanted muskellunge returned from spawning sites to the same lake in which they were captured and implanted. Of the 24 tagged muskellunge, four were harvested via angling or spearing within 1 year after tagging, and two additional fish were assumed harvested when contact was lost. Implanted muskellunge tended to remain in the lakes during the winter, then move into spawning areas in spring, eventually returning to open lake sites where they resided over summer. Muskellunge movement behavior diverged after spawning each year, with 11 tagged fish (61.1 %) remaining in Skegemog or Clam Lake for the summer, and seven individuals traveling to Elk or Torch Lake. Muskellunge home ranges averaged 612 ha and ranged from 17 to 5,287 ha.
Muskellunge spawning habitat and reproductive success
Reproduction of muskellunge Esox masquinongy has failed in many waters that formerly supported self-sustaining populations. Laboratory experiments were conducted to isolate causes of such failures. Differential mortality occurred among lots of muskellunge eggs incubated in jars of unaceated lake water over substrates of sand, gravel, silt, aquatic macrophytes, wood, tree leaves, polyethylene screen, and bare glass. High and rapid early mortality (days 1–2), attributable to low dissolved oxygen (DO) concentrations (0–0.1 mg/liter), occurred among eggs incubated on leaves and macrophytes. After day 3, Saprolegnia sp. fungus was implicated in high egg mortalities in jars with inorganic substrates and moderate DO concentrations (3.8–4.1 mg/liter). Lowest mortality rates occurred on organic substrates (silt and wood) amidst intermediate DO concentrations (0.4–1.7 mg/liter) and limited fungal infestation. Among eight midwestern lakes and reservoirs, measured DO at the substrate-water interface in four of them was high (means, 6.0–8.4 mg/liter) and showed little microstratification; these lakes contain self-sustaining muskellunge populations. The other four lakes showed extreme DO microstratification and virtual anoxia (means, 0.4–2.4 mg/liter) at the substrate-water interface; muskellunge populations in these lakes are supported almost wholly by stocking. Suitable spawning substrates in these lakes are aerated by annual reservoir drawdown, have inherently low biological oxygen demand, or support dense beds of stonewort Chara sp. Reproductive failure is associated with spawning areas having deep accumulations of organic matter and dense macrophyte growth. Improvements of spawning habitat to prevent or alleviate hypoxia are among the options available to manage this species.
Factors affecting recruitment of age-0 muskellunge in Escanaba Lake, Wisconsin, 1987-2006
We modeled variation in recruitment (R) of age-0 muskellunge Esox masquinongy to identify factors influencing their abundance in Escanaba Lake, Wisconsin. Muskellunge R declined over the study period and ranged from 0.00 to 1.85 age-0 fish/km of shoreline (mean = 0.42 age-0 fish/km of shoreline). A Ricker stock–recruitment model determined that the following factors explained 88% of the variation in annual R of age-0 muskellunge between 1987 and 2006: abundance and age structure of the adult muskellunge population, abundance of bluntnose minnow Pimephales notatus, abundance of age-3 and older (age-3+) walleyes Sander vitreus, abundance of age-0 white suckers Catostomus commersonii, and coefficient of variation (CV) of May water temperatures. Abundance of adult muskellunge (≥76.2 cm total length) accounted for only 1% of the variation in R and showed no significant relationship with R. Abundance of bluntnose minnow improved the model fit to 40% of the variation in R and indicated that higher R was achieved with greater numbers of bluntnose minnow. The average age of adult muskellunge further improved the model fit to 59% of the variation in R, suggesting that R increased when more young adults were present in the population. The abundance of age-3+ walleyes enhanced the model fit to 69% of the variation in R and indicated that greater R occurred with high numbers of walleyes. The abundance of age-0 white suckers improved the model to explain 77% of the variation in R and indicated that more recruits occurred when numbers of age-0 white suckers were low. Finally, the CV of May water temperatures further improved the model to explain 88% of the variation in R and signified that lower variability in May water temperatures was beneficial to recruitment success. We interpret the model results to mean that muskellunge R in Escanaba Lake is regulated by the reproductive potential of the adult muskellunge population, forage availability, variation in May water temperatures, and other community dynamics.
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.