Samples from 1971 to 1993 demonstrated that the composition of the crustacean zooplankton community of Lake Superior has changed. Specifically, the abundance of large-bodied zooplankton has decreased significantly in the past two decades. Populations of a pelagic planktivore, the lake herring (COREGONUS ARTEDI), have concurrently increased, suggesting a process of selective predation. Examining the components of planktivory to elucidate this phenomena in a lake the scale of Superior, I assessed the encounter, pursuit, attack, capture and ingestion of zooplankton by lake herring. I stereoscopically videotaped lake herring feeding experiments to determine angles of elevation and bearing with reactive distance. Reactive volume, a novel approach, was calculated from these parameters; reactive volume addresses encounter, pursuit and attack for cruising pelagic fish. Capture success was also obtained from videotape analysis. I measured lake herring gill arches and zooplankton body dimensions to address retention. The probabilities associated with these steps of the planktivory process were combined in a model to predict stomach contents of lake herring. Validated with field caught lake herring, the model averages 80% accuracy, usefully simulates lake herring feeding behavior, and provides a basis for addressing numerous management and theoretical issues.