Understanding predator diets is fundamental to marine ecology, yet soft-bodied prey tissues are often extensively digested before analysis. Fish sagittal otoliths are highly resistant to digestion and provide a robust method for reconstructing predator diets through prey identification, size reconstruction, abundance estimation, and biomass estimation. Despite their widespread application in fisheries science, otolith-based methods remain underutilised for quantitative dietary reconstruction in marine predator studies.
This study demonstrates the application of fish otoliths for quantitative dietary reconstruction in coastal dolphins from Southeast Queensland (SEQ). Stomach contents from stranded or bycaught Tursiops aduncus, Sousa sahulensis, and Delphinus delphis collected between 2024 and 2025 were examined. Recovered sagittal otoliths were identified to the lowest possible taxonomic level using reference collections and published identification guides. Diet composition was quantified using frequency of occurrence (%FO), numerical abundance (%N), and the Index of Relative Importance (%IRI). Prey total length and biomass were reconstructed from otolith morphometrics using published species-specific regression equations.
A minimum of 16 prey taxa were identified. Teleost fishes comprised the dominant prey group, with Gerres, Sardinops, and Atherinomorus representing the principal prey taxa. Otolith morphometrics enabled reconstruction of prey size distributions and biomass, providing a more comprehensive assessment of dietary composition than prey occurrence or abundance alone.
This study highlights the value of fish otoliths as durable biological indicators for quantitative dietary reconstruction and demonstrates how fisheries-based otolith methodologies can be applied to investigate predator–prey interactions in marine ecosystems. These approaches provide a repeatable framework for trophic ecology studies and demonstrate the broader utility of otolith science beyond traditional fisheries applications.