Aggregation in organisms is often mediated by aggression between members of the group and between groups. The goal of this work is to explore such interactions and their influence on the spatial structure of a population and the mortality it experiences. The motivation behind this work is an attempt to understand the distribution and interactions between groups of marine organisms. Situations considered include fish schools where the mortality is due to predation falls but at the expense of forage success because of interference with one’s companions and the expected distribution of extremely aggressive organisms such as swordfish. In the latter case, it is hypothesized that acoustic sensory clues will lead to spatial patterns by setting a comfort range between fish. This and an understanding of forage and physical cues allows a description of their use of frontal environments. The effects of fratricide and cannibalism on the distribution and population dynamics are explored. This includes consideration of swordfish and cannibalistic schooling fish such as cod and pollock. In this last case, the interaction is age structured. Finally, it is pointed out that this type of model could also be used to understand the behavior of fisheries directed at different types of fish.