PNNL

Abstract

Strontium isotopes (87Sr/86Sr) recorded in the otoliths of Pacific Salmon (Oncorhynchus spp.) are commonly used to trace natal origins. However, maternally sourced dietary contributions from the yolk to otolith 87Sr/86Sr during embryonic development can confound determination of provenance when it differs from the 87Sr/86Sr of the natal rearing water. For species that migrate at or soon after emergence, the embryonic region of the otolith may provide the only record of natal origin. We experimentally quantified maternal and exogenous diet contributions to otolith 87Sr/86Sr over embryonic development in Kokanee salmon (O. nerka). Eggs obtained from two populations in isotopically distinct lakes were incubated and reared in a common water supply intermediate to the 87Sr/86Sr of the source lakes. Timing of developmental events and the proportional contribution from yolk to otolith 87Sr/86Sr differed significantly between the two populations. We suggest that the magnitude of difference in 87Sr/86Sr between the yolk and water and the concentration of Sr in these isotopic sources are likely driving this variation, as well as potential population-specific effects on otolith growth and composition. Understanding of these transitions can provide useful information for studies of provenance in species and populations in which natal site rearing is limited or absent.