Elemental fingerprints of otoliths of fish may distinguish estuarine 'nursery' habitats

The elemental fingerprints or composition of otoliths of fish may provide a natural tag of the 'nursery' habitat of juvenile fish. The natural tag could then be used to determine the 'nursery' habitat of adult fish found on coastal reefs. We collected juvenile Pelates sexlineatus from 2 to 5 sites within each of 7 estuaries to determine whether elemental composition of otoliths differed among estuaries and among sites within estuaries. In addition, fish were collected in 2 successive years to determine whether temporal differences may be found in elemental fingerprints that could then confound subsequent assignment of adults to 'nursery' estuaries. Significant differences in elemental fingerprints (Sr, Ba and Mn) were found within and among estuaries, but there was often an interaction with time suggesting that there were differences among estuaries/sites but the difference varied between times. Quadratic discriminant functions (QDFs) generated to discriminate among estuaries suggested that the QDFs calculated from a single year class were more successful at assigning fish to the correct estuary than either (1) QDFs based on both years combined or (2) using the QDFs generated from the first year class to classify the second year class. Small-scale variability among sites within an estuary suggested that for an estuarine fishery we may be able to classify fish to their site of origin; this warrants further investigation. Adult fish from a coastal fishery can now be assigned to their 'nursery' estuary by analysing the juvenile region of their otoliths, provided that discriminant functions are generated from the appropriate year class of recruits.