Science Response 2021/012
Ecological Impact of Water-Level Drawdown on Lake Chubsucker (Erimyzon Sucetta) in the St. Clair National Wildlife Area
Context
The St. Clair National Wildlife Area (NWA) is a 352 ha wetland complex located on the east shore of Lake St. Clair in the municipality of Chatham-Kent, Ontario. Between 1940 and 1980, a series of dykes, pumps, and other water control structures were installed within the St. Clair Unit to maintain water levels in the East and West wetland cells. Dyking was necessary to maintain wetted area and other habitat functions in the face of drainage modifications to the surrounding landscape and due to ongoing water-level fluctuations of Lake St. Clair (ECCC 2018).
Management of the St. Clair NWA is the responsibility of the Canadian Wildlife Service of Environment and Climate Change Canada (ECCC). Currently, thirty five species (birds, reptiles, insects, fishes, vascular plants) listed under the Species at Risk Act (SARA) occur within the NWA. The area is also internationally recognized as an important migratory stopover for numerous waterfowl and other migratory bird species. The management plan for the St. Clair NWA (ECCC 2018) identifies periodic water-level drawdown through the dyke and pump system as a necessary activity to maintain a diverse, native aquatic vegetation community, similar to the water-level fluctuations experienced in an undyked coastal wetland. Periodic drying of soils is aimed at rejuvenating the seed bank of native aquatic plants and achieving hemi-marsh conditions (described as an equal ratio of vegetated and open water), but may also allow for targeted removal of exposed plants, such as American White Water-lily (Nymphaea odorata) and the invasive European Common Reed (Phragmites australis subsp. australis).
Water-level drawdown was proposed for 2020, which was intended to achieve a 95% reduction of water volume over a five month period in the East cell of the St. Clair Unit. Although the long-term maintenance of native aquatic vegetation imposed by such a drawdown may benefit fishes within the cell, concern exists that drawdown will impose substantial mortality or other negative effects on Lake Chubsucker (Erimyzon succetta), SARA listed as Endangered, owing to stranding or other effects (e.g., increased predation by waterbirds; Bouvier and Mandrak 2011). DFO’s Species at Risk and Fish and Fish Habitat Protection programs have requested that DFO Science provide advice on the potential impact of water-level drawdown on Lake Chubsucker; namely, to identify: 1) the relationship between drawdown increment and available refuge habitat for Lake Chubsucker in the East cell; 2) the relationship between habitat availability and Lake Chubsucker abundance; and, 3) the potential for deep water habitat creation in advance of drawdown to increase available refuge.
This Science Response Report results from the Science Response Process of May 14, 2020 and February 9, 2021 on the Ecological Impact of Water-Level Drawdown on Lake Chubsucker (Erimyzon Sucetta) in the St. Clair National Wildlife Area.
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