Temporal and spatial variability in elemental composition of otoliths: implications for determining stock identity and connectivity of populations

Interannual variability in elemental composition of otoliths may confound spatial interpretations. The elemental fingerprints of otoliths of juvenile fish were determined for fish collected from 12 to 15 estuaries in each of three consecutive recruitment years to determine temporal variation in otolith chemistry for each estuary. It was also examined whether there is overlap in elemental fingerprints of fish collected in different years and from different estuaries that may confound subsequent spatial comparisons. Significant differences in otolith chemistry were found among years for individual elements (lithium, manganese, strontium, and barium) and for multi-element fingerprints. Some estuaries showed large variation in multi-element fingerprints among years, whereas others showed little variation among years. There was some overlap of elemental fingerprints of different estuaries, but these were not always for fish collected in the same year. The significant spatial and temporal variation in elemental fingerprints meant that it was possible to confound spatial differences with temporal differences. Therefore, if the natal estuary of the adults is to be determined, a library of elemental fingerprints needs to be built up over time for each estuary rather than a single year-class of juveniles being used as the elemental fingerprint for a number of year-classes of adults.