Experimental Assessment of the Magnitude and Sources of Lake Sturgeon Egg Mortality

Mortality during early life stages can greatly affect annual recruitment. Despite the importance to population abundance and community composition, quantitative estimates of the sources and magnitude of early life mortality in natural environments are generally lacking for many fish species. We conducted a field experiment to quantify egg mortality during incubation for Lake Sturgeon Acipenser fulvescens. Fertilized Lake Sturgeon eggs were placed in replicated exclosures in the Black River, Michigan, at a known spawning location. Incubation conditions were modified using four exclosure treatments differing in mesh size that simulated different levels of access by predators and water flow regimes (0.1-0.6m/s). Egg mortality through 80% of the incubation period was high (average 91%) and varied significantly (75-97%) across treatments. Treatments with reduced predator access and low water velocity experienced the highest levels of cumulative egg mortality. Developmental arrest was a larger source of mortality (84%) than the combined effect of predation and scour or de-adhesion (16%). We also documented a significant treatment by time (day of incubation) interaction, indicating that although cumulative rates of mortality may not vary significantly among spawning sites, the relative contributions of different sources of mortality can vary greatly at different times during egg incubation. Received October 28, 2012; accepted March 25, 2013