Partial migration occurs when a population contain both migratory and resident individual. It is a wide-spread phenomenon across the animal kingdom. We are motivated by one of the classic example of salmonid fishes (Oncorhynchus, Salmo, and Salvelinus) that breed in streams, but contain some individuals that migrate to an ocean or lake and others that complete their entire life cycle in the stream. We study several discrete-time population models both linear and non-linear to investigate the coexistence of migrants and residents. We prove that a locally defined fitness quantity (R0) determines the global dynamics of the system: if it is less than one, the population goes extinct and if larger than one, then there exist a stable equilibrium point which is a state stable coexistence of both resident and migratory individual.