Evaluating the Efficacy of Ecological Restoration of Fish Habitat in Coastal Waters of Lake Ontario

Ecological restoration is a common strategy applied to degraded wetlands and tributaries in large lakes. As resources are typically limited for restoration, it is essential to ensure that such efforts achieve associated goals. Using both discrete and continuous methods, we evaluated the efficacy of ecological restoration efforts on fish habitat within Canada's largest city, Toronto, (Cell 2 and Embayment D of Tommy Thompson Park) relative to a control site (Toronto Islands). First, we used a long-term electrofishing dataset (i.e., discrete) to examine catch and community composition relative to restoration status. Restoration was generally effective in that catch for northern pike (Esox lucius) remained constant at both restoration sites, and invasive common carp (Cyprinus carpio) decreased at Embayment D, indicating that exclusion barriers may be effective. Restoration may not have been as effective for largemouth bass, as catches remained similar after restoration at Cell 2, but decreased within Embayment D. We also found that relative abundance for coldwater species at both restoration sites decreased post-restoration, with increases in warmwater species at Cell 2 and coolwater species at Embayment D. Next, we used a long-term acoustic telemetry dataset (i.e., continuous sampling) with three focal species: largemouth bass, northern pike, and invasive common carp. Based on telemetry, we found that restoration efficacy was species-specific, with largemouth bass present before and after ecological restoration (particularly in spring, which may be associated with spawning), but clear reductions in use of the restored areas for common carp and northern pike. Exclusion barriers, while effective for non-native common carp, appeared to also influence access for northern pike. Using both discrete and continuous methods provided complementary information on the efficacy of restoration works within Toronto Harbour with electrofishing data highlighting changes in fish community composition while acoustic telemetry provided continuous information on timing and duration of habitat use.