The Use of Longitudinal and Cross-Sectional Photographic Data to Study Skin Disease in Wild Bottlenose Dolphins (Tursiops truncatus )

Many populations of bottlenose dolphins (Tursiops truncatus) inhabit coastal and estuarine waters near highly populated and developed areas, which make them susceptible to anthropogenic and terrestrial threats from pollution and runoff Pathogens historically considered to be terrestrial and zoonotic have been identified in bottlenose dolphins ( Tursiops truncatus) in recent years, possibly indicating a shift in host preference or the emergence of new diseases in naive populations. This project utilized a visual assessment approach for evaluating small cetacean health based on the prevalence, extent, and etiology of observed skin lesions and specific diseases such as lacaziosis. The prevalence of skin lesions and occurrence of different lesion types were examined among free-ranging bottlenose dolphins from three different sites in the southeastern United States (Charleston, SC; Brunswick and Sapelo, GA; Sarasota Bay, FL). The prevalence of skin lesions for the three sites ranged between 37-58% and comparisons between sites revealed significant differences in the occurrence of skin lesions, as well as differences in lesion types. A similar seasonal trend in lesion prevalence was observed for all three sites, and regression modeling revealed associations between lesion occurrence and colder water temperatures. Lacaziosis was used as a model skin disease for epidemiologic investigations of infected dolphins from Sarasota Bay and Charlotte Harbor, Florida. Approximately 2-3% of the dolphins in both populations were infected with lacaziosis or lacaziosis-like disease, and these estimates were robust to alterations in estimation methodologies. Descriptive analyses of a case series of dolphins in Sarasota Bay indicated that lacaziosis and lacaziosis-like disease were most common among adult males, and lesions were primarily located on the extremities. Case-control analyses for lacaziosis and non-lacaziosis dolphins in Sarasota Bay revealed differences in the spatial distribution and clustering of sightings, a ten-year difference in the median survival time, and social associations that suggested a non-communicable transmission pathway. Growth modeling of lacaziosis lesion progression among three lacaziosis cases from Sarasota Bay showed some individual variation in lesion progression and a gradual decrease in lesion growth over time. Furthermore, truncated modeling approaches revealed that 5-10 years of longitudinal photographic data may be sufficient for the development of similar models in other populations. Recent efforts to assess the health of wild dolphin populations have used capture and release methods; however, such methods require substantial effort, risk and cost, and are not appropriate across a broad geographic or temporal scale. Longitudinal and cross-sectional photographs of well-known bottlenose dolphin populations can be used as a non-invasive approach to develop epidemiological studies to better understand the demographic, geographic, and environmental variables that may contribute to skin disease susceptibility, transmission, and sources/reservoirs. Developing efficient means to monitor disease occurrence in these sentinel species ultimately serves as a surveillance system to track current and future emerging pathogens.