Otolith Sr/Ca ratio complements Sr isotopes to reveal fish migration in large basins with heterogeneous geochemical landscapes

Abstract

The potential use of Sr/Ca and Ba/Ca ratios in fish otolith, as a complement to 87Sr/86Sr to study movements of Prochilodus lineatus, was evaluated in the La Plata Basin (South America). Water ratios were obtained from samples collected during the high and low water seasons at 42 sites across the La Plata Basin. Elemental and isotopic ratios in water were measured by MC-ICP-MS, ICP-MS and ion chromatography, and obtained from available literature. Fish were caught from six different sites with different physiochemical features. Otolith core-to-edge Sr/Ca and Ba/Ca profiles were determined by LA-ICP-MS, while the otolith 87Sr/86Sr data set was taken from literature. The predictive classification by rivers according to water Sr/Ca, Ba/Ca and 87Sr/86Sr ratios (92.5%) was higher than that based solely on 87Sr/86Sr (58%), with classification that reached 100% for several rivers. Unlike Ba/Ca, a significant relationship (R2 = 0.94, p < 0.05) was found between otolith edge and water Sr/Ca, suggesting that this could be an efficient movement indicator for P. lineatus. The Sr/Ca ratio complemented the information provided by Sr isotopes and it was particularly useful in the northwest basin, where the isotopes alone do not allow differentiating between large rivers.