Spatiotemporal variability in otolith core elemental fingerprints to assess natal origin of Atlantic halibut (Hippoglossus hippoglossus) in the Gulf of St. Lawrence

After declining in the 1950s, Atlantic halibut (Hippoglossus hippoglossus Linnaeus, 1758) in the Gulf of St. Lawrence (GSL), Canada, has shown a marked comeback since the early 2000s, now ranking as the most valuable groundfish resource. Given its socio-economic importance, understanding larval ecology and early life stages is key to sustainable management. Spawning occurs in deep GSL channels, with individuals exhibiting summer site fidelity. More recently, otolith chemistry has provided insights into early life history and movement. In this study, edges and cores of 187 otoliths from halibut with known migration histories were analyzed using Laser Ablation Inductively Coupled Plasma Mass Spectrometry (LA-ICP-MS) to identify nursery contributions. Magnesium (Mg), Strontium (Sr), and Barium (Ba) characterized spatial differences in otolith elemental fingerprints. Four cohorts (2006, 2007, 2009, 2010) were examined to assess temporal trends in nursery contributions. Our findings suggest that Atlantic halibut in the GSL forms a philopatric population with multiple nurseries, and that natal origin does not influence later migration strategies. Given the role of early life stages in stock recruitment, these insights enhance our understanding of natal sources and their contributions to the stock, supporting more informed management strategies.