Population dynamics of muskellunge in Wisconsin waters of Green Bay, Lake Michigan, 1989-2005

Muskellunge, Esox masquinongy, were an important component of the Green Bay ecosystem prior to mid 1900s, but were extirpated by over-fishing, pollution, habitat degradation, and the introduction of exotic species. The Green Bay ecosystem improved after the passage of the Clean Water Act, and the Wisconsin Department of Natural Resources (WI DNR) started a muskellunge reintroduction program in 1989. Monitoring the results of reintroduction efforts is necessary to achieve the program goal of establishing a self-sustaining population. We used available data to provide a 2005 spawner abundance estimate for a Green Bay tributary, estimates of contributions to that spawning stock from fall fingerling and yearling stocking, a weight–length relationship, a growth analysis, and a description of size and age at maturity. Our results indicate that stocking efforts have been successful in producing an adult population, with yearlings contributing to the spawning stock at a higher proportion than fingerlings (14.69:1). Our weight–length and growth analyses suggest that Green Bay muskellunge are unlikely to reach record length, but that it is possible for females to achieve record weight. The rapid growth of Green Bay muskellunge results in their maturing at larger sizes than other stocks, but the relationship between age and maturity is not well understood. Reintroduction efforts in Green Bay have created stocked populations capable of supporting trophy fisheries, but evidence of successful natural reproduction has not been observed. Future research should focus on the reproductive requirements of muskellunge reintroduced into altered habitats.

opulation dynamics and angler exploitation of the unique muskellunge population in Shoepack Lake, Voyageurs National Park, Minnesota

A unique population of muskellunge Esox masquinongy inhabits Shoepack Lake in Voyageurs National Park, Minnesota. Little is known about its status, dynamics, and angler exploitation, and there is concern for the long-term viability of this population. We used intensive sampling and mark–recapture methods to quantify abundance, survival, growth, condition, age at maturity and fecundity and angler surveys to quantify angler pressure, catch rates, and exploitation. During our study, heavy rain washed out a dam constructed by beavers Castor canadensis which regulates the water level at the lake outlet, resulting in a nearly 50% reduction in surface area. We estimated a population size of 1,120 adult fish at the beginning of the study. No immediate reduction in population size was detected in response to the loss of lake area, although there was a gradual, but significant, decline in population size over the 2-year study. Adults grew less than 50 mm per year, and relative weight (W r) averaged roughly 80. Anglers were successful in catching, on average, two fish during a full day of angling, but harvest was negligible. Shoepack Lake muskellunge exhibit much slower growth rates and lower condition, but much higher densities and angler catch per unit effort (CPUE), than other muskellunge populations. The unique nature, limited distribution, and location of this population in a national park require special consideration for management. The results of this study provide the basis for assessing the long-term viability of the Shoepack Lake muskellunge population through simulations of long-term population dynamics and genetically effective population size.

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.

Vital statistics of Esox masquinongy in Nogies Creek, Ontario: Population size, natural mortality and effects of fishing

Several methods for the estimation of population size and natural mortality are used and evaluated, for the Nogies Creek maskinonge, with consideration being given to the sources of error and correcting factors discussed by Muir (1963a). The Schumacher tagging method and a method using only catch and average exploitation are found to be equally useful.The same catch and exploitation method is used to estimate natural mortality and the estimates agree with those from the Beverton and Holt type method. Both methods suffer from large year-to-year errors but the 9-year average appears to be a useful statistic. Natural mortality increases with age and is about 15% per year for age IV and older and about 24% per year for age V and older.There is only a 2-fold variation in the estimated age IV size of year-classes. The smallest of 9 year-classes was 302 and the largest was 604. No effect of fishing on subsequent year-class production could be demonstrated during the period of study. Heavy fishing did, however, remove large numbers of older fish with a resultant increase in catchability of the younger fish.