Impacts of declining water levels on the quantity of fish habitat in coastal wetlands of eastern Georgian Bay, Lake Huron

There are >3,700 coastal wetlands along 4,500 km of eastern Georgian Bay (GB), providing critical spawning and nursery habitat for migratory fish of Lake Huron. Sustained low water levels since 1999 have led to the loss of fish habitat due to severance of wetlands from GB. We estimate (1) the amount of fish habitat that has already been lost between the historic high water level (177.5 m asl) and current levels (176.11 m asl) using a site-specific approach for seven wetlands and (2) the magnitude of loss if water levels were to decrease as predicted by global circulation models (GCMs) using a regional method that is applicable to all of eastern and northern GB. Maximum depth of wetland outlets (162.94–176.06 m asl) was used to estimate the cumulative area of habitat that would become hydrologically disconnected as water levels decline. If water levels were to drop to 175.33 m asl, as predicted by one GCM, 13% of the total number of coastal wetlands and 6% of the total area in coastal wetlands would disappear in addition to what has already been lost. For both the methods, the rate of habitat loss was greatest between 173 and 176 m asl.