• journal_title：Geology
• Contributor：B. Lynn Ingram ; Peter K. Weber
• Publisher：Geological Society of America
• Date：1999-
• Format：text/html
• Language：en
• Identifier：10.1130/0091-7613(1999)027<0851:SOICSS>2.3.CO;2
• journal_abbrev：Geology
• issn：0091-7613
• volume：27
• issue：9
• firstpage：851

Geochemical methods for distinguishing salmon of different runs would improve management practices designed to mitigate for declines in salmon populations in California's Sacramento–San Joaquin river system. Strontium isotopic measurements show a strong relationship between the ⁸⁷Sr/⁸⁶Sr ratio in hatchery water and the ⁸⁷Sr/⁸⁶Sr ratio in the otoliths (aragonitic ear bones) of juvenile chinook salmon (Oncorhynchus tshawytscha) raised in those waters. As a result of differences in basin geology from north to south along the western slope of the Sierra Nevada, important salmon spawning rivers within the Sacramento–San Joaquin river system have distinct ⁸⁷Sr/⁸⁶Sr ratios. Of the 10 rivers in this study, those in the Sacramento River drainage have lower ⁸⁷Sr/⁸⁶Sr ratios (0.7039–0.7063) than those in the San Joaquin River basin (0.7068–0.7092), with the exception of the American River, which has the highest ⁸⁷Sr/⁸⁶Sr ratios in this study (average 0.7100). The combination of distinct river ⁸⁷Sr/⁸⁶Sr ratios and the relationship between water and otolith Sr isotope ratios indicates that this geochemical method can be used to identify the origin (and potentially the migration history) of juvenile, out-migrating salmon in the Sacramento–San Joaquin system.