Comparison of the diets of sympatric dugongs and green turtles on the Orman Reefs, Torres Strait, Australia

Abstract

This study investigated the diet of dugongs (Dugong dugon- Fam. Dugongidae) and green turtles (Chelonia mydas- Fam. Cheloniidqe) on the Orman Reefs in Torres Strait, between Australia and Papua New Guinea, where large numbers of these animals live sympatrically. The stomach contents of dugongs and green turtles caught in an Indigenous fishery were examined. Dugongs fed exclusively on seagrasses (mainly Thalassia hemprichii, Cymodocea spp. and Syringodium isoetifolium) whereas turtles consumed both seagrasses (especially Thalassia hemprichii and Enhalus acoroides) and algae (mainly Hypnea spp., Laurencia spp. and Caulerpa spp.). The two herbivores did not show overlap in resource use except for the seagrass Thalassia hemprichii which was abundant in the feeding area. Both species appeared to feed selectively and did not just consume the most available food items. These results are suggestive of partitioning of food resources between dugongs and green turtles but a full explanation requires more detailed, and concurrent, study of the food resources and the animals’ movements.