Preliminary results for the investigation of natal origin in capelin (Mallotus villosus) from the Gulf of St. Lawrence using otolith chemistry

This study investigates the use of otolith elemental fingerprints to infer natal origin and habitat connectivity of capelin (Mallotus villosus) in the Gulf of St. Lawrence (GSL). Otolith elemental fingerprints were extracted from capelin larvae, juveniles and adults collected throughout most of the GSL in 2022 and 2023. Larval otolith elemental fingerprints differed significantly from the larval otolith portion (core) of juveniles and adults. Elevated elemental concentrations in the larval otolith fingerprints, beyond values observed in juvenile and adult cores, currently impedes the assignment of post-recruit individuals of unknown origin to a specific location. Despite this challenge, our results confirm that geographic variability in environmental conditions in the GSL produced distinct elemental fingerprints, reinforcing the reliability of otolith chemistry for tracking capelin movements. Random Forest clustering of elemental fingerprints from juvenile and adult core otoliths identified two putative natal origins in the population. The contributions of these two natal sources indicated some geographic structuring of juveniles, especially in the southern GSL (sGSL). Adult contributions of each source were similar in the Estuary but dominated by one natal source in the sGSL. We discuss implications for future otolith chemistry analyses and provide recommendations for upcoming sampling and data analysis.