Development of a multi-scale wetland Resilience Index from muskellunge nursery habitat in Georgian Bay, Lake Huron

In a 2012 study, no age-0 muskellunge (Esox masquinongy) were found in any of 16 historic nursery sites in coastal marshes of southeastern Georgian Bay (SEGB), and this was attributed to sustained low water levels (1999-2013) that had altered the vegetation structure of nursery habitat. In the same study, age-0 muskellunge were found in 16 coastal marshes surveyed in northern Georgian Bay (NGB), even though these sites had been subjected to the same water-level conditions. We hypothesize that hydrogeomorphic features of NGB sites made them resilient to effects of sustained low lake levels that made the SEGB sites unsuitable for age-0 muskellunge. Compared to their SEGB counterparts, the NGB nursery sites were significantly steeper, deeper, and less sheltered under low water levels. We used these hydrogeomorphic features to develop a multi-scale Resilience Index (RI) for identifying coastal wetlands that are resilient to stable low lake levels. The RI correctly classified the NGB and SEGB nursery sites, with an area-under-the-curve score of 0.973. Coarser-scale variants of the RI provide a regional screening tool in the identification of resilient wetland habitat (e.g. potential muskellunge nursery habitat), and a basin-wide approach to identify vulnerable wetland habitats. This multi-scale index, in conjunction with targeted field surveys, should provide managers a useful tool in the face of uncertain water level forecasts.