Potential Changes in the Thermal Habitat of Great Lakes Fish after Global Climate Warming

We estimated potential changes in the size of thermal habitat of representative cold-, cool-, and warmwater fish for southern Lake Michigan and the central basin of Lake Erie before and after simulated global climate warming. Observed midlake thermal structures were modeled (BASE) and then manipulated with three general circulation climate models (OSU, GISS, GFDL) that projected warmer climates when atmospheric carbon dioxide concentrations were doubled. Under BASE conditions, on an annual basis, lake trout Salvelinus namaycush had the largest thermal habitat in southern Lake Michigan, coho salmon Oncorhynchus kisutch and yellow perch Perca flavescens had smaller thermal habitats, and largemouth bass Micropterus salmoides had none. Even for lake trout, the suitable thermal habitat was only 5–20% of the upper 200 m through the year. With rare exceptions, thermal habitat increased for species in all thermal guilds for all climate-warming scenarios. No thermal habitat was estimated for coldwater fish in the central basin of Lake Eric because the hypolimnion becomes anoxic in summer. The median increase in thermal habitat was 2.5 × BASE condition both for southern Lake Michigan and the central basin of Lake Erie. After climate warming, minimum thermal habitat during summer decreased for walleye Stizostedion vitreum, increased for yellow perch, and remained the same for lake whitefish Coregonus clupeaformis and lake trout. Fish yields estimated from published empirical models that relate thermal habitat in summer to maximum sustained yields remained about the same for lake trout and lake whitefish but increased for walleye. The general conclusions were that the sizes of the habitat favorable for cold-, cool-, and warmwater fish would increase in Lake Michigan, whereas the habitats favorable only for cool-, and warmwater fish would increase in Lake Erie.