Landscape approach to evaluating fish habitat, population dynamics, and regulations in Michigan lakes

We describe a landscape approach for estimating fish thermal habitat, growth potential and the timing of fish reproduction for all lakes in Michigan.  We used published regression equations, a geographic information system, and statewide information on climate and lake fetch to predict the average seasonal temperature cycles for 10,000 lakes in Michigan at least five acres in surface area.  We found a delay in the date of peak water temperature as lake size increases, from July 18 for 10-acre lakes to August 15 for 10,000-acre lakes.  We used estimated daily temperatures to predict the timing of spawning and duration of nesting for smallmouth bass as if they occurred in all Michigan lakes.  We predict that in many lakes, adult male smallmouth bass will still be nesting at the start of the catch-and-keep bass season.  Using a standard bioenergetics model, we computed length at age 6 as an index of relative growth of largemouth bass for all lakes.  This index was weakly correlated with mean surface temperature, but strongly correlated with cumulative degree days.  This landscape approach was useful for assessing habitat conditions, estimating population dynamics, and evaluating effectiveness of regulations for all lakes in the state.