Assessment of winter size-selective mortality of young-of-the-year Atlantic salmon (Salmo salar) using otolith microstructure analysis

The objectives of this study were, first, to assess the usefulness of otolith microstructure analysis to examine winter size-selective mortality of young-of-the-year (YOY) Atlantic salmon and, secondly, to validate various hypotheses relating to the dynamics of two populations with different winter survival. By examining otolith microstructure, we back-calculated body size at hatching and at emergence of YOY salmon sampled in fall 2000 and in early summer 2001 on the Petite Cascapedia River and the Bonaventure River (Quebec, Canada). The results of the study did not reveal any size-selective mortality of YOY salmon in the Petite Cascapedia River, while in the Bonaventure River, size-selective mortality of the smaller individuals of the cohort was detected. This case study allowed not only a better comprehension of the population dynamics of those rivers but demonstrated the usefulness of otolith analysis to detect winter size-selective mortality under a natural environment.