Migratory contingents, groups of individuals belonging to the same population that adopt different migratory patterns, have been identified in numerous Striped Bass (Morone saxatilis) populations along North American East Coast. We tested the hypothesis that migratory contingents may develop early in life to maximize the exploitation of the variety of habitats faced by a recently introduced fish population. Using the discriminatory power provided by otolith chemistry, we studied early-life history stages of Striped Bass in a recently reintroduced population in the St. Lawrence Estuary. Migratory patterns were inferred using multivariate analysis of four otolith trace elements (Sr, Ba, Mn, and Mg) on juveniles (0+ and 1+). Three migratory contingents were identified during early-life history stages: freshwater residents, oligohaline migrants, and mesohaline migrants. This study demonstrates the rapid establishment, in less than 10 years since initial stocking, of three migratory contingents initiated early in life among the St. Lawrence Striped Bass population. We postulate that diversification provided by the establishment of distinct migratory contingents among earlylife history stages promotes the rapid colonization of new environments through the exploration and exploitation of an increased number of nursery habitats