Otolith sulfur isotope method to reconstruct salmon (Oncorhynchus tshawytscha) life history

We report a new ion microprobe method to reconstruct aspects of fish life history based on sulfur isotopes ( 34 S/ 32 S, expressed as δ 34 S). Selected hatchery raised and naturally spawned juvenile chinook salmon (Oncorhynchus tshawytscha) are shown to have a 12.96 ± 0.27‰ (mean ± 2 standard errors) difference in muscle δ 34 S values, corresponding to δ 34 S differences between the hatchery and freshwater diets. Isotopic microanalyses of otoliths demonstrate that this 13‰ difference is preserved in the otoliths. We interpret the otolith δ 34 S record to be a chronology of dietary δ 34 S, with approximately one-week temporal resolution, preserved in these banded calcium carbonate structures. Potential applications of this method include identifying hatchery raised fish and reconstructing nutrition sources, migration, and other aspects of fish life history.