Cooperative Fish and Wildlife Research Units Program: Washington
Education, Research and Technical Assistance for Managing Our Natural Resources

Summary 1. Understanding the limits of consumption is important for determining trophic influences on ecosystems and predator adaptations to inconsistent prey availability. Fishes have been observed to consume beyond what is sustainable (i.e. digested on a daily basis), but this phenomenon of hyperphagia (or binge-feeding) is largely overlooked. We expect hyperphagia to be a short-term (1-day) event that is facilitated by gut volume providing capacity to store consumed food during periods of high prey availability to be later digested. 2. We define how temperature, body size, and food availability influence the degree of binge-feeding by comparing field observations with laboratory experiments of bull trout (Salvelinus confluentus), a large freshwater piscivore that experiences highly variable prey pulses. We also simulated bull trout consumption and growth during smolt outmigrations under two scenarios: 1) daily consumption being dependent upon bioenergetically-sustainable rates, and 2) daily consumption being dependent upon available gut volume (i.e. consumption is equal to gut volume when empty, and otherwise “topping off” based on sustainable digestion rates). 3. One-day consumption by lab-held bull trout during the first day of feeding experiments after fasting exceeded bioenergetically-sustainable rates by > 80-fold at low temperatures (3° C) and by ~1.3-fold at 20° C. The degree of binge-feeding by bull trout in the field was slightly reduced but largely in agreement with lab estimates, especially when prey availability was extremely high (during a sockeye salmon [Oncorhynchus nerka] smolt outmigration and at a counting fence where smolts are funnelled into high densities). Consumption by bull trout at other settings were lower and more variable, but still regularly hyperphagic. 4. Simulations demonstrated the ability to binge-feed increased cumulative consumption (16-32%) and cumulative growth (19-110%) relative to only feeding at bioenergetically sustainable rates during the ~1 month smolt outmigration period. 5. Our results indicate the ability for predators to maximize short-term consumption when prey are available can be extreme and is limited primarily by gut volume, then mediated by temperature; thus predator-prey relationships may be more dependent upon prey availability than traditional bioenergetics models suggest. Binge-feeding has important implications for energy budgets of consumers as well as acute predation impacts on prey.