Simulations of Cisco Fish Habitat in Minnesota Lakes under Future Climate Scenarios

This report makes projections of potential (refuge) habitat for cisco, a coldwater fish, in Minnesota lakes under projected warmer climate scenarios. It is about the identification and selection of potential refuge lakes for cisco under future climate scenarios in Minnesota. This is the third and final project report in a series that describes computer model simulations of cisco (tullibee) lakes for the Minnesota Department of Natural Resources (DNR). The first report gave an overview of the characteristics of cisco lakes in Minnesota, the second gave results of water quality (temperature and dissolved oxygen, DO) model simulations for selected Minnesota cisco lakes, and this third report identifies and quantifies in which Minnesota lakes cisco habitat is most likely to continue to exist under global warming scenarios. Cisco habitat simulations were first made for continuous, year-round weather time series from 1962 to 2008 (47 years) at the daily time scale. Simulations were then extended to projected future climate scenarios. A year-round water quality model MINLAKE 2010, that had previously been calibrated against 7384 pairs of temperature and DO data points measured in 28 lakes between 1979 and 2008 with overall standard errors of 1.47 oC for water temperature, and 1.50 mg/L for DO, was used in all cisco habitat simulations (Fang et al. 2010). Adult cisco habitat is limited by critical water temperature and DO conditions in different strata of a cisco lake. The selection was based on the oxythermal parameter TDO3, which relates to the survival stress of adult cisco. The lower the TDO3 is, the lower the stress is to cisco. TDO3 is a water temperature that occurs where DO = 3 mg/L and was used as the oxythermal parameter to select suitable habitat for adult cisco (Jacobson et al. 2010). Twelve TDO3 parameters ranging from single-day values to multi-year averages, and from extreme values to mean values, were defined in Table 3.1 and calculated from simulated daily temperature and DO profiles. The multi-year values AvgATDO3FB and AvgATDO3VB were ultimately chosen from Table 3.1, lines 6 and 12, for the selection of cisco refuge lakes. Each of these two TDO3 parameters is calculated over the length of a 31-day benchmark period; one uses a fixed benchmark period from DOY 209 to DOY 239 (July 28 to August 27); the other uses a variable (sliding) benchmark period of 31 days.