Critical demographic and ecological factors are often more closely related to ontogenetic stage or size than to age. Two stage-structured models under development for describing fish community dynamics on Georges Bank funded by the NOAA Coastal Ocean Program are illustrated. The first is a simple two-stage model comprising juveniles and adults of a group of interacting species. This model is defined in discrete time in a delay-difference formulation. The model describes survivorship from the previous time step and the addition to the population through recruitment.
Interspecific interactions can occur at both the juvenile and adult stages.
For highly nonlinear recruitment functions, a broad array of dynamical behavior including stable points, cycles and chaos is possible for even simple two species systems. Harvesting and interspecific interactions are shown to have synergistic effects on the dynamics of the system. Such models can readily give rise to multiple stable states in community structure. These models are also considerably more demanding with respect to data requirements. The objective of NOAA Coastal Ocean Program studies on Georges Bank is to develop models of exploited multispecies systems in support of fishery management which can accommodate these factors.