Determination of temperature-dependent otolith oxygen stable isotope fractionation on chum salmon Oncorhynchus keta based on rearing experiment

Reconstruction of water temperatures experienced by marine fishes using otolith oxygen stable isotopes ( δ 18 O) as natural thermometers has been proven to be a useful approach for estimating migration routes or movement patterns. This method is based on the mechanism that the equilibrium fractionation of δ 18 O otolith against ambient water exhibits a species-specific thermal sensitivity during the process of otolith aragonitic CaCO 3 precipitation. In this study, a laboratory-controlled rearing experiment was conducted to determine the temperature dependency of δ 18 O fractionation on the anadromous fish species, chum salmon ( Oncorhynchus keta ), of which the detailed migration routes have not been elucidated yet. To test that temperature was the only factor affecting δ 18 O otolith fractionation, this study ensured a relatively stable rearing condition, evaluated the isotope composition of the rearing water, and analyzed carbon isotope ( δ 13 C otolith ) to examine the potential effect of kinetic and metabolic isotopic fractionations. The δ 18 O otolith fractionation equation on chum salmon was thereby determined within a temperature range of 9–20°C and was indistinguishable from the equation of synthetic aragonite; The δ 13 C otolith was affected by both physiological processes and δ 13 C DIC ; In lower temperatures settings, both oxygen and carbon isotopes depleted simultaneously. This study suggests that the chum salmon species-specific oxygen isotope fractionation equation could be used on reconstruction of temperature history and also throw insights into understanding the incorporation of oxygen and carbon sources during calcification process for otoliths.