The research involved development of two ecological simulation models to explain the complex dimensionality of chinook salmon (Oncorhynchus tshawytscha) life history structure (represented by the age composition of the spawning stock) and management difficulties entailed in the complexity. Since different sizes of chinook salmon are thought to adapt differently to heterogeneous habitats, age composition of the spawning stock is determined by characteristics of the habitats of the substocks. Numerical properties of substocks result from the incorporation of individual spawners in different age classes and each substock performs differently because their age compositions are distinctive. A stock or population consists of substocks whose age compositions are concordant with their habitats. The productive capacity of a population will result from the incorporation of substocks. If habitat structures of streams are different, the age and size compositions and productive capacity of the populations may differ. Selective harvesting affects spawners in different ways, so that age compositions must be deformed differently by fishing pressure. Once the age composition deviates from the natural age composition, the productivity of the population will decrease. Population dynamics are strongly correlated with substock structure which is determined by habitat structure in a stream system. Hierarchical population structure make fisheries management difficult and requires not only quantitative but also qualitative analysis on the populations in relation to habitat classification. / Graduation date: 1990