Epidemiological investigation of tattoo-like skin lesions among bottlenose dolphins in Shark Bay, Australia

Abstract

Bottlenose dolphins are excellent bioindicators of ocean ecosystem health for three reasons: (a) as long-lived apex predators they accumulate biotoxins and contaminants; (b) they are visible, routinely appearing at the water's surface in coastal areas, often coming into close contact with humans; and, (c) they exhibit a range of pathogenic lesions attributable to environmental degradation. In this study, we analyzed tattoo-like skin lesions in a population of Tursiops aduncus studied for 30+years in Shark Bay, Australia, a UNESCO World Heritage Site. We provide important baseline data by documenting epidemiological patterns of tattoo-like skin lesions in a healthy, free-ranging population that builds on the previous data of tattoo skin disease (TSD) derived from free ranging, stranded, and dead dolphins. Individual dolphins were classified as symptomatic with tattoo-like skin disease if at least one photograph showed a lesion similar to TSD. The average age of infection was 26.6months (±34.8months) with the symptomatic period lasting 137±29.8days. Overall prevalence of tattoo-like skin disease in the population was 19.4%. Age, but not sex, was significant, with yearlings (1–2years) exhibiting tattoo-like lesions more than younger and older calves. Tattoo-like lesions were rare among juvenile and adult dolphins (N=68 calves, 4 juveniles, and 3 adults). We hypothesize that the lower prevalence in youngest calves (<1year) is due to maternal immunity, while older individuals (>2years) have infection-acquired immunity, as reported for other small cetaceans. The low prevalence of tattoo-like lesions in Shark Bay compared to other populations with poxvirus is consistent with reproductive and demographic viability analyses. Furthermore, by documenting the demography of the disease, we can monitor changes in the prevalence of tattoo-like lesions as a sentinel indicator of ecosystem health.