Recent evidence suggests that lake whitefish (Coregonus clupeaformis) populations in lakes Huron and Michigan now intermix considerably during non-spawning periods, while lake whitefish stocks continue to be largely treated as discrete, independent units for management and assessment purposes, and stock status is usually assessed in each unit annually. The goals of my thesis were to: 1) compare fishery management performance and assessment estimation performance based on the current spatial structure for assessments (assuming non-mixing unit stocks) and two alternative approaches to addressing mixing among stocks, and 2) evaluate changes in performance that might results from less frequent assessments. The current target mortality rate (65%) was maintained in both chapters. I modeled the dynamics of four intermixing, age-structured populations using a management strategy evaluation framework to evaluate assessment approaches and frequencies. In chapter 1, I found that the relative performance of pooled and separate population assessments depends on mixing rates and productivity. While pooling can sometimes be advantageous, it can also sometimes lead to substantial overfishing, likely due to bias or inappropriate allocation among areas. In chapter 2, the results showed that compared to other things, like the actual mixing among areas and the choice of how to account for spatial structure, the frequency of assessment had modest effects. When conducting an annual assessment, removing the 1-year lag had little influence. My results suggest that conducting assessments every three or five years should be considered as part of a management strategy and may allow analytical efforts to be directed in other ways.
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