A Pre-Restoration Assessment of Reef Spawning Habitat in Saginaw Bay

Saginaw Bay is a shallow, productive embayment that serves as key nursery habitat for a diversity of fish species. Historically, rocky reefs provided spawning structure for many species, including Walleye (Sander vitreus) and Lake Whitefish (Coregonus clupeaformis). These reefs likely provided many benefits, including spatio-temporal diversification of spawning and protection from egg predation. Sedimentation due to intensive land-use led to the loss of most historical reef structure. As sedimentation patterns have seemingly decreased, there has been increased momentum towards reef restoration in Saginaw Bay. The purpose of this study was to analyze spawning patterns of two key fish species, Walleye and Lake Whitefish, and to determine the potential usage of restored reef habitat. We evaluated sites at varying degrees of reef degradation. We measured environmental conditions, abundances of spawning fish, egg deposition, and egg predation. After a two-year study, we have documented spawning fish and egg deposition at multiple locations, suggesting that populations may be able to capitalize on improved reef structure. However, egg deposition rates and densities of spawning fish were low and various predators consumed Walleye and Lake Whitefish eggs. We suggest that reef restoration may attract additional fish to spawn and provide protection against egg predation.