Estimation of fish population dynamics are often based on age structures. Understanding past population structure is of interest to evolutionary biologists because it can reveal when migration regimes changed in natural populations, thereby pointing to potential environmental factors such as climate changes as driving evolutionary forces. Characterizing the structure of extent populations is also key to conservation genetics as translocation or reintroduction decisions must preserve evolutionary stable units. Finally, population structure has important biomedical consequences either when a number of subpopulation groups is locally adapted to particular environmental conditions (and maladapted when exposed to new environments) or represents a confounding factor in the study of the statistical association between genetic variants and phenotyp