Scale microchemistry as a non-lethal alternative for tracking individually variable migration patterns in mobile fish

Estuaries are important habitats to many coastal fishes. Some species of fish can use the low salinity and freshwater environments that estuaries provide, though the exact patterns of usage for these habitats for some species is not well understood. Stable isotope and microchemical analysis of fish otoliths and muscle tissue have been used to analyze fish migratory behavior in many studies, especially in the case of euryhaline fishes. However, removal of otoliths and muscle tissue require the sacrifice of the subject organism. Scales are another structure of fish that experience deposition of stable isotopes and elements from the environment during their formation, and the removal of scales for most species is a non-lethal process. For this study, Red Drum Sciaenops ocellatus were collected in bays and estuaries along coastal Texas and analyzed for a suite of chemical assays including stable isotope (𝛿 13C and 𝛿 15N) and trace element (strontium and barium) composition of scales. Scale chemistry was compared among fish collected in bays that differed in their distance from freshwater inflow sources to assess divergence in terrestrial influence as well as degree of fish residency in isotopically distinct food webs. Scale stable isotopes and elements are often compared to determine if different chemical markers support comparable conclusions about movement or residency. Scale chemistry compositions were compared to prior analyses of otoliths and muscle isotope compositions to assess agreement in chemical history information between structures that can be sampled lethally and nonlethally. Stable isotope signatures of muscle tissue and scales were closely matched. Qualitative analysis of elemental profiles of scales and otoliths did not reveal any clear matching trends, though they will be further examined to determine if pattern matching is present.