Partitioning Maternal And Exogenous Diet Contributions To Otolith Sr-87/Sr-86 In Kokanee Salmon (Oncorhynchus Nerka)

Strontium isotopes (Sr-87/Sr-86) recorded in the otoliths of Pacific salmon (Oncorhynchus spp.) are commonly used to identify natal origin. For species that migrate at or soon after emergence, the embryonic region of the otolith provides the only record of provenance. However, maternal contribution of Sr from the yolk can confound the isotopic signature of the natal site. We experimentally quantified maternal and exogenous diet contributions to otolith Sr-87/Sr-86 over embryonic development in kokanee salmon (Oncorhynchus nerka). Eggs from two populations in isotopically distinct lakes were incubated and reared in a common water source. Timing of developmental events and proportional contribution from yolk to otolith Sr-87/Sr-86 differed significantly between the two populations. We suggest that the magnitude of difference in Sr-87/Sr-86 between yolk and water, the relative concentrations of Sr and Ca in these isotopic sources, and population-specific effects on otolith growth and composition contribute to this variation. Understanding how these factors affect otolith Sr-87/Sr-86 could extend the use of otolith geochemistry for determining provenance to species and populations in which natal site rearing is limited.