Changing occurrence of epidermal lesions in wild bottlenose dolphins

There are increasing concerns that human activities promote the development of natural diseases in aquatic organisms. Of these, diseases concerning small cetaceans have received increasing attention. Most studies have focused on dead animals and provided information on pathogens, contaminant exposure and probable causes of death. However, our understanding of diseases in Living populations, particularly with respect to prevalence during the Lives of individuals, and for whole populations in different years, remains limited. This study was designed to provide such information on epidermal lesions (abnormalities not directly attributable to physical trauma that may indicate disease) in a wild population of bottlenose dolphins Tursiops truncatus. An 8 yr time series of photographs of 82 free-ranging dolphins from NE Scotland was used to investigate the occurrence and dynamics of epidermal lesions in 7 age classes of young dolphins (from their Ist to their 7th summer of life) and for an adult group. Lesions were found at high prevalence (90 to 100%) in both young and adult dolphins, with Ist-summer calves having the lowest levels. Lesions of different appearance showed 2 patterns of occurrence, either being restricted to young individuals or becoming more common with age. When severity was compared between calves (in their 2nd summer of life) born in 8 different years, a significant decline over time was observed (p < 0.005). Comparison of this change with environmental and anthropogenic factors may help identify which factors may be promoting the ubiquitous epidermal lesions in these dolphins.