What did you say about my mother? The complexities of maternally derived chemical signatures in otoliths

Connecting maternal migratory behavior with the behavior and ecology of their progeny can reveal important details in the ecology of a population. One method for linking maternal migration to early juvenile life history is through maternal chemistry recorded in otoliths. Despite the wide use of maternal signatures to infer anadromy, the duration and dynamics of maternal otolith signatures are not well understood. Shifts in the elemental ratios and strontium isotope ( ⁸⁷ Sr/ ⁸⁶ Sr) chemistry in otoliths from juvenile Chinook salmon (Oncorhynchus tshawytscha) correlate with the timing of hatch and emergence, respectively, indicating a chemical marker of these ontological stages. Additionally, analysis of maternal signatures show that maternally derived ⁸⁷ Sr/ ⁸⁶ Sr may be influenced by equilibration of the mother to fresh water, and in some cases the ⁸⁷ Sr/ ⁸⁶ Sr signatures of the eggs can shift substantially after being laid. These results provide guidance in separating maternal and juvenile signatures as researchers increasingly target early juvenile otolith chemistry. These results also caution against the use of ⁸⁷ Sr/ ⁸⁶ Sr alone as a marker of anadromy in populations with major inland migrations.