Pathology of green sea turtle (Chelonia mydas): Mortalities in Gladstone Harbour, Queensland, Australia, 2017–2020

Queensland, in northeastern Australia, is host to some of the most biodiverse and important marine ecosystems in the world, with the Great Barrier Reef being one of the most critical and well-known coral reef systems in the world. Green sea turtles (Chelonia mydas) are amongst the iconic species inhabiting the region, with important rookeries and foraging grounds found along the Queensland coast. Gladstone Harbour, in Central Queensland, is one such foraging ground, representing an important habitat for post-pelagic juvenile, subadult and adult green sea turtles. It is also the site of Queensland's largest multicommodity port, containing the world's fourth largest coal exporting terminal, as well as holding busy recreational fishing and commercial net fishing grounds.The expansion of the port over the last century has resulted in significant changes to the marine habitat, with seagrass beds and mangroves ecosystems physically degraded, increased pollution and increased shipping traffic. As part of a port-specific monitoring programme for the turtle populations, green sea turtles found stranded (n = 22), either dead or euthanized due to non-rehabilitative conditions, between 2017 and 2020 were subjected to comprehensive post-mortem examination to determine underlying morbidities and the cause of death. Many of the turtles (9/22) were in poor nutritional condition, and most had cardiovascular inflammation and/or gastroenteritis, although the blood fluke parasite (Digenea: Spirorchiidae) burden was generally low to moderate. Trauma, caused by boat strikes and occasional shark attack, was another relatively frequent finding. Overall, the findings point to considerable impact from habitat loss and degradation, pollution and vessel strikes caused by human activities and modifications of the ecosystem in the port and surrounding areas leading to malnutrition and likely weakening the immune system of the turtles. The findings may inform approaches to mitigate some of these anthropogenic impacts in the future.