The goals of this research were to: 1) investigate how intermixing of populations affected the performance of the 65% total mortality control rule that is currently used to manage lake whitefish (Coregonus clupeaformis) fisheries in the 1836 Treaty waters (TW) of the Great Lakes; and 2) explore the performance of alternative mortality rates for lake whitefish fisheries in the 1836 TW under different intermixing and productivity scenarios. The simulation framework that was developed modeled the dynamics of four intermixing, age-structured fish populations with varying levels of productivity. The framework also included a full age-structured assessment of the mixed fisheries, with abundance, mortality and recruitment estimates from these assessments used in combination with harvest control rules to set total allowable catches for stocks. In chapter 1, the 65% total mortality control rule was found to perform poorly in terms of protecting lower productivity populations. Yields from areas occupied by low productivity populations were often similar in magnitude to areas occupied by high productivity populations as a result of intermixing, which could result in managers thinking low productivity populations could be fished more intensively. In chapter 2, 45% and 55% total mortality control rules were found to perform better than the current control rule in ensuring population sustainability, maximizing yields, and increasing yield stability under certain productivity and intermixing levels. Alternative control rules resulted in mortality rates similar to what has been estimated for lake whitefish stocks in the 1836 TW, reducing the potential effects on commercial fishers if the control rule was indeed changed to this lower mortality rate.
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