Improved methods for understanding the role of predation on dreissenid population dynamics

Impacts of dreissenid mussels (Dreissena spp.) on Great Lakes ecosystems are well documented, and a better understanding of mechanisms that cause variation in dreissenid abundance is needed. An outstanding question is how much dreissenid biomass is consumed by fish predation. A significant difficulty for investigating dreissenid consumption by fish is that dreissenids in stomachs are often a mix of indigestible shell and flesh, which can bias bioenergetics models and estimates of daily ration. Here, we develop an analysis to convert crushed shell and flesh mixtures found in fish diets to dry weight of digestible dreissenid flesh. Quagga Dreissena rostiformis bugensis and zebra Dreissena polymorpha mussels were used in separate dry weight analyses simulating stomach contents ranging from individual mussels to aggregates of each species. A species-specific dry weight relationship was observed when comparing flesh-only dry weight to total dry weight (shell + flesh) for individual dreissenid but not for aggregates. Thus, the model is applicable in providing more precise estimates of dreissenid flesh dry weight in fish diets.