Temperature dependence of δ 18 O in otolith of juvenile Japanese sardine: Laboratory rearing experiment with micro-scale analysis

We evaluated the use of the stable oxygen isotope (δ 18 O) in the otolith as a proxy for the temperature history of Japanese sardine Sardinops melanostictus individuals. Japanese sardine juveniles were reared in three different water temperatures over the course of a month. Otolith δ 18 O ( δ otolith ) was analyzed by extracting the portions formed during the rearing period using a micromill. δ 18 O of the rearing water ( δ water ) was also analyzed. A linear relationship between otolith δ 18 O and ambient water temperature was identified as follows: δ otolith − δ water = −0.18 * T + 2.69 (r 2 = 0.91, p Sardinops spp., with resulting application to wild Japanese sardine captured in the Pacific Ocean showing that it estimates a more realistic in situ temperature. Our findings suggest that the Japanese sardine-specific isotopic fractionation equation should be used when interpreting otolith δ 18 O of the Japanese sardine, and the methods presented here could also be useful to understand the temperature history of other fish species.