Epidermal diseases in bottlenose dolphins: impacts of natural and anthropogenic factors

Experimental studies have highlighted the potential influence of contaminan ts on marine mammal immune function and anthropogenic contaminants are comm only believed to influence the development of diseases observed in the wild . However, estimates of the impact of contaminants on wild populations are constrained by uncertainty over natural variation in disease patterns under different environmental conditions. We used photographic techniques to com pare levels of epidermal disease in ten coastal populations of bottlenose d olphins (Tursiops truncatus) exposed to a wide range of natural and anthrop ogenic conditions. Epidermal lesions were common in all populations (affect ing >60% of individuals), but both the prevalence and severity of 15 lesion categories varied between populations. No relationships were found between epidermal disease and contaminant levels across the four populations for w hich toxicological data were available. In contrast, there were highly sign ificant linear relationships with oceanographic variables. In particular, p opulations from areas of low water temperature and low salinity exhibited h igher lesion prevalence and severity. Such conditions may impact on epiderm al integrity or produce more general physiological stress, potentially maki ng animals more vulnerable to natural infections or anthropogenic factors. These results show that variations in natural environmental factors must be accounted for when investigating the importance of anthropogenic impacts o n disease in wild marine mammals.