Using Fish Scales As Non-Lethal Alternatives to Otoliths to Track Migration of Atlantic Tarpon

A growing field in connectivity is the use of chemical signatures in biogenic hard parts as proxies for provenance and migration.  However, non-lethal alternatives to structures such as otoliths are required when investigating species where mortality must be avoided.  We investigated the chemical properties of scales from the highly migratory Atlantic tarpon Megalops atlanticus in the Gulf of Mexico to track connectivity patterns and movements across estuarine gradients. We found significant differences in chemical signatures from scales collected from separate geographic regions. Within scales, we observed consistent enrichments in δ¹⁵N values indicating ontogenetic trophic shifts and individual variation in the remaining proxies (Sr:Ca, Ba:Ca, and δ¹³C) that reflected differential patterns of movement between marine and upper estuarine waters. Notably, values of δ¹³C were positively related to Sr:Ca in all geographic regions, suggesting that scale δ¹³C values primarily reflected movement across salinity gradients rather than fractionation associated with trophic increases. Multi-proxy chemical analysis of Atlantic tarpon scales therefore provides a non-lethal alternative to otolith geochemistry for identifying connectivity, migration and trophic patterns of this highly mobile species.