Size-based dynamics of a demersal fish community: Modeling fish-fisheries interactions

This thesis defends a holistic approach to fish dynamics, supports size as a factor determining functional groups in a community, and presents a model that can serve as a framework for the integration of biological knowledge of fish communities with decision-making about resource exploitation.; We discuss the aspects that should be considered to approach the study of fish species dynamics. In their natural environment fish species dynamics are influenced by the presence of other species. Interacting species form a community that lies at the core of this thesis. Fishery and survey data show drastic changes in the Newfoundland demersal fish community during the period from the late 70s to the early 90s.; We use these changes to analyse size as an indicator of species response to fisheries. We find that size at the community level can substitute for species to determine functional groups that direct community dynamics.; This size-based approach shows properties of the community that cannot be explained by looking at each single species one at a time. Thus, a size-based simulation model is built to analyse long-term community dynamics and its response to fisheries. The model has only three simple assumptions: (1) fish pass through a series of age-determined size classes through their life history, (2) big fish eat little fish, and (3) predation cannot drive species to extinction. The model is stable over runs of centuries, and from a stabilized state can be used to explore several scenarios involving environmental and fishery disturbances.