Epidemiology of tattoo skin disease in bottlenose dolphins Tursiops truncatus from the Sado estuary, Portugal.

We report on the epidemiology of tattoo disease in a community of bottlenose dolphins Tursiops truncatus from the Sado estuary, Portugal. The presence of tattoos (T++) and tattoo-like (T+) lesions was examined in 586 photographic records of 35 dolphins taken from 1994 to 1997. Images were rated into 3 categories: good (GI), average (AI) and poor (PI). Dolphins positive for T++ lesions were observed in 19 GI. Dolphins with T+ lesions were seen in 39 GI, 23 AI and 6 PI. For statistical analysis the dolphins were divided into 2 age classes (immature and adult) and the data grouped into 2 periods (1994-1995 and 1996-1997). Minimum prevalence of T++ lesions in 32 dolphins was 21.9% in 1994-1995 and 15.6% in 1996-1997. Variation in prevalence of tattoo disease between the 2 age classes was examined for each period, excluding animals with T+ lesions or considering them either positive or negative for tattoos. Prevalence of the disease was significantly higher in immature dolphins than in adults during both periods, except in the first one when T+ lesions were considered as true tattoos. Temporal variation in prevalence of tattoo disease was examined in 23 adults. Prevalence was significantly higher in 1994-1995 (39.1%) than in 1996-1997 (17.4%). Differences in the number and quality of pictures did not cause significant biases that could have favoured the detection of lesions between age classes or periods. Minimal persistence of the disease ranged between 3 and 45.5 mo. The lesions converted into light grey marks when healing, but may recur. The presence of very large lesions in 2 adult dolphins affected for years may be related to the contamination of the estuary. The high prevalence of the disease, its long persistence, as well as higher frequency in immature individuals, suggest that it is endemic in bottlenose dolphins from the Sado estuary. The contribution of tattoo disease to the decline of this community should be investigated. Three of the 5 dolphins that died during this study had T++ and T+ lesions.