Michigan Department of Natural Resources
Fisheries Research Report No.1838, 1976

Biological Basis for Management of Lake Whitefish in the Michigan Waters of Northern Lake Michigan


Mercer H. Patriarche


      Abstract.-Stocks of lake whitefish have supported an intensive commercial fishery in the Michigan waters of Lake Michigan for over a century. However, certain biological indicators suggest that recent upsurges in the catch reflect overfishing, and fish managers are instituting measures to assure a stabilized population and fishery. A biological basis for establishing quotas is described in this paper, using information from the 1968-1973 commercial fisheries in statistical districts MM-1 and MM-3 and a modification of Ricker's dynamic pool model. Natural mortality rates computed for an unfished population of whitefish in the lower end of nearby Grand Traverse Bay were important components of the model.

Quota recommendations were based on the premise that the annual harvest should be confined to weight gained each year by the harvestable portion of the population. Six computations of equilibrium yields were made. A comparison of actual harvests and adjusted yields revealed an annual overharvest, on the average, of 30% during this period in the two statistical districts.

Total biomass for six age groups (I-VI) in three Michigan statistical districts of northern Lake Michigan was computed to be 21.9 million kilograms in 1972. In MM-1 and MM-3, approximately 15.6 million kilograms (18.3%) of the total biomass was susceptible to exploitation. Corrected 1972 yields based on both biomass calculations and the modified dynamic pool model produced adjusted yields that differed by only 1.5%. A change in the minimum size limit (from 432 to 482 mm) to build up a depleted stock also was discussed. Increased spawning stock, more spawning opportunities and greater egg deposition should result from this regulation change.