Mémoire
| Résumé : | The dugong (Dugong dugon) is a long-lived marine mammal widely distributed throughout the Indo-Pacific region and listed as Vulnerable to Extinction. Dugongs are obligate benthic seagrass specialists, supplementing their diet with maternal milk for the first three or more years of life. Their specialised diet makes them especially susceptible to seagrass habitat degradation and loss; potentially leading to nutrient deficiencies and delayed reproduction. Dugong tusks grow continuously and are the only teeth present throughout life in all individuals. Tusk growth layer groups (GLGs) are deposited annually and can potentially be used as a physiological record of a dugong’s life. This study conducted stable isotope analysis (SIA) of tusk dentinal collagen to examine dietary shifts (d13C, dietary source; d15N, trophic level) over the lifetime of an individual, including ontogenetic and environmentally elicited-changes.Mean d15N value decreased significantly in dugongs, from ‘calf < 3 yo’ (6.19 ± 0.26 ‰, n = 9) to ‘adult’ (5.44 ± 0.22 ‰, n = 10) indicative of a shift from a milk-based diet to a fully herbivorous diet. Temporal variation in carbon and nitrogen isotope signatures and ontogenetic dietary shifts can be shown. This novel approach provides retrospective individual dietary information that cannot be shown through current methods of dietary analysis and is difficult to obtain via direct observations of an elusive free-ranging species. By providing insights into the dietary composition of an individual dugong, SIA of tusks combined with historical meteorological data may be able to investigate dietary shifts in dugongs after severe weather events. |
