Sex differences in the epidemiology of tattoo skin disease in captive common bottlenose dolphins (Tursiops truncatus): are males more vulnerable than females?

The clinical and epidemiological features of tattoo skin disease (TSD), caused by cetacean poxviruses, are reported in 257 common bottlenose dolphins (Tursiops truncatus) held in 31 facilities in the USA and Europe. Photographs and biological data of 146 females and 111 males were analyzed. Dolphins were classified into three age classes (0-3; 4-8; over 9 years), approximating the life stages of 'calves and young juveniles', 'juveniles and sub-adults' and 'adults'. The youngest dolphins with tattoos were 14 and 15 months old. Minimal TSD persistence varied between 4 and 65 months in 30 dolphins and was over 22 months in those with very large lesions (> 115 mm). In 2012-2014, 20.6% of the 257 dolphins had TSD. Prevalence varied between facilities from 5.6% (n= 18) to 60% (n= 20), possibly reflecting variation in environmental conditions. Prevalence was significantly higher in males (31.5%) than in females (12.3%), a pattern which departs from that observed in free-ranging Delphinidae where there is no gender bias. As with free-ranging Delphinidae, TSD prevalence in captive females varied with age category, being the highest in the 4 to 8 year old. By contrast, prevalence levels in males were high in all age classes. Prevalence of very large tattoos was also higher in males (28.6%, n= 35) than in females (11.1%, n= 18). Combined, these data suggest that captive male T. truncatus are more vulnerable to TSD than females possibly because of differences in immune response and because males may be more susceptible to captivity-related stress than females.