Michigan Department of Natural Resources
Fisheries Research Report No.1804, 1973
Response of the Bluegill Population and
Fishery of Mill Lake to Exploitation
Rate and Minimum Size Limit: a
Simulation Model
James C. Schneider
Abstract.-The effects of fishing on a typical, but slow-growing population of bluegills in Mill Lake were simulated. Hypothetical fisheries were generated by varying exploitation rate and age of entry. Corresponding changes in the catch and in the size and structure of the bluegill population were predicted. Certain combinations of exploitation rate and age of entry (forming the eumetric line) produced the highest sustained yield to the angler. The analysis also showed that minimum size limit should be increased-up to a maximum of 6. 0 inches-as exploitation rate increases. Overexploitation, in terms of wasting potential yield or depleting the spawning stock, will not occur if size limits or fishing rates are managed so that the fishery is operating at or above the eumetric line. A bluegill fishery, typical of southern Michigan lakes (m
= 30%, size limit about 5. 5 inches", produced a yield of about 7 kg (90 bluegills) per hectare. The numbers of bluegills larger than 5. 0 and 7. 0 inches which remained in the lake were 77% and 34%, respectively, of the highest number possible.