Nahiid Stephens

The current state of sea turtle health in the Indian Ocean is largely unknown, especially for the endemic flatback turtle (Natator depressus) which is listed as ‘vulnerable’ in Western Australia (WA) and ‘data deficient’ globally. Anecdotally, the causes of illness, injury, and death in Western Australian turtles are comparable to those in other parts of Australia and the world (e.g., spirorchiidiasis, fibropapillomatosis, and marine debris interaction) but scientific studies to validate these reports are particularly limited in this region. To address these knowledge gaps, causes of both live and dead turtle strandings in WA were investigated through an array of veterinary diagnostic techniques including necropsy, clinical pathology, diagnostic imaging, histopathology, parasitology, microbiology, toxicology, and molecular analyses. Health assessments were conducted on live animals to determine baseline levels of health and disease for specific populations, predominately nesting and foraging flatback turtles.

Through these health and disease investigations, baselines were developed, along with the discovery of new diseases in flatback turtles including a novel haemoparasite, Haemocystidium spp., occurring specifically in the foraging life stage; a potentially emerging zoonotic bacterium, Streptococcus iniae associated with a multi-species mass mortality event involving post-hatchlings; as well as spirorchiidiasis, previously unreported in this species. Other unusual and emerging diseases were also reported in sea turtles in this study, including microsporidial myopathy, salt gland adenitis, gout, and pseudogout.

In this study, natural disease-related causes of mortality occurred more frequently than direct anthropogenic causes, with parasitoses the most frequently occurring natural disease. Spirorchiidiaisis was the most common cause of mortality (32.0%) with a prevalence of 93.2% in turtles susceptible to the disease (i.e., excluding the post-hatchling life stage). The next most common cause of mortality was unknown (17.3%), followed by trauma (13.3%), endoparasitosis (10.7%), infectious disease (6.7%), and pneumonia (6.7%), with the remaining mortality categories each accounting for less than 5% of cases (including systemic inflammation, osmoregulatory disorder, gastrointestinal impaction, gastrointestinal foreign body, fibropapillomatosis, and metabolic disorder).

We developed the first flatback turtle reference intervals (RIs) in Reference Value Advisor (RefVal v2.1) following the American Society of Veterinary Clinical Pathology (ASVCP) guidelines. We found flatback turtle RIs were generally similar to other published sea turtle RIs and reference values (RVs) but detected significant differences in our study for the various boundary conditions including life stage (nesting or foraging), as well for measurement methodology (field or laboratory tests), justifying the establishment of separate RIs/RVs for nesting and foraging flatbacks, and for field and laboratory techniques.

This study was the first sea turtle health and disease investigation in WA and the eastern Indian Ocean to offer broader insights into sea turtle health and disease status on a regional scale. These essential baselines provided a number of crucial functions which include serving as a reference point for future studies to monitor changes in population health and disease levels. Specifically, these baseline data will be useful for future comparative studies of the same population where changes are an indication of a changing environment. The blood RIs can be used for disease diagnosis, monitoring progress and assessing prognosis of clinical flatback turtle cases in rehabilitation. Considering that diseases in the marine environment are predicted to rise with increasing anthropogenic pressures, detection of new and emerging diseases is of significance to the global knowledge of sea turtle diseases; and for understanding and mitigating disease threats to sea turtle populations. Finally, this study provided a framework to integrate health into future conservation management decisions to ensure the long-term survival of sea turtles.