Multi-year stability of spatial patterns in capelin otolith-edge chemical fingerprints in the Gulf of St. Lawrence, Canada

In the Gulf of St. Lawrence (GSL, Canada), the population structure and dynamics of capelin ( Mallotus villosus ), an abundant small pelagic forage fish, remain poorly understood, limiting the implementation of reliable stock assessment. Otolith-edge elemental signatures were analysed to identify regions with statically distinct element signatures and evaluate the potential of otolith chemistry as a tool for tracking capelin movements and life history events in the GSL. A total of 679 individuals were collected between 2022 and 2024, and their otolith elemental composition was analysed using Laser Ablation Inductively Coupled Plasma Mass Spectrometry (LA-ICP-MS). Seven elements (lithium, boron, magnesium, potassium, zinc, strontium, and barium) were retained for discriminating among three regions: Estuary, South and Strait of Belle Isle (SBI). Quadratic discriminant analysis (QDA) assigned individuals to their region of origin with reallocation success rates of 64.3 % for the Estuary, 60.0 % for the South, and 80.5 % for the SBI. A sensitivity analysis confirmed the robustness of the results and indicated a negligible effect of individual length. Although some interannual variability was detected over the three-year period, spatial differences consistently exceeded temporal variation. Spatial differences in elemental signatures likely reflect underlying oceanographic drivers, such as water temperature and salinity, which influence otolith-edge chemistry. These results indicate that otolith-edge elemental fingerprints can provide significant discrimination among regions, supporting their potential use in studies of capelin movement and spatial population structure. Such information may ultimately contribute to improved stock assessment and management in the GSL. • Capelin otolith edge chemistry used to study temporal stable spatial in the Gulf of St. Lawrence water. • Seven elements identified to discriminate three chemically distinct regions. • Spatial differences exceeded temporal variation over three years. • Provides chemical baseline to improve capelin stock assessment and management.