An individual-based approach to predicting density-dependent dynamics in smallmouth bass populations

The dynamics of a young-of-the-year cohort of a fish species, smallmouth bass (Micropterus dolomieui), were modeled using an individual-based computer simulation model. The young-of-the-year fish were simulated from the egg stage until recruitment into the yearling age class. At low initial densities of smallmouth bass in the swim-up larvae stage, recruitment to the yearling age class was roughly proportional to the initial densities of larval fish. However, when the initial densities were sufficiently high decreasing recruitment was observed as a function of further increases in larval density in the model. This occurred because high initial densities prevented all but a small fraction of the smallmouth bass from attaining large enough sizes to escape winter starvation. The addition of significant levels of size-dependent predation greatly altered this result, however. Heavy predation reduced the competition for prey among smallmouth bass and allowed a large number of smallmouth bass to grow rapidly and recruit to the yearling class.