Given its ecological and socioeconomic importance, the Atlantic tomcod (Microgadus tomcod (Walbaum, 1792)) population of the St. Lawrence estuarine transition zone is the focus of conservation efforts and requires a better understanding of its population dynamics. Here, we use otolith microchemistry to define the structure of the St. Lawrence tomcod estuarine population and identify the key contributing spawning grounds. We rely on two sampling surveys, otolith microchemistry data, and machine-learning approaches to identify two main sources contributing to the tomcod stock recruitment. The main source contributed approximately two-thirds of the recruitment, whereas the second source accounted for the residual third. Both sources exhibited distinct temporal and spatial habitat use in the St. Lawrence estuarine transition zone, highlighting questions regarding the presence of multiple stocks within the population. Our findings emphasize the importance of identifying the main contributing natal sites to fish stock recruitment when implementing effective management plans in the context of increased environmental change and human activities affecting aquatic ecosystems.
Landry-Massicotte et al. (Fri,) studied this question.