Using mark-recapture and stranding data to estimate reproductive traits in female bottlenose dolphins (Tursiops truncatus) of the Southwestern Atlantic Ocean

Despite bottlenose dolphins being well studied in several regions around the world, there is very limited information about the reproduction of these animals in the Southwestern Atlantic Ocean (SWA). In this study, data from a long-term mark-recapture and stranding monitoring program were used to estimate life history traits of female bottlenose dolphins inhabiting the Patos Lagoon estuary, a sub-tropical coastal region in the SWA. From the analysis of 32,296 high-quality dorsal fin photographs, the fate of 37 individual females and 66 of their calves was tracked. Results supported a birth pulse dolphin community, with most births occurring during late spring and summer, in association with increasing water temperature and food supply. Female bottlenose dolphins first reproduced at a minimum age of 8 years. Mean inter-birth interval was 3 years (mode = 2), and fecundity was 0.11. A clear change in the delta C-13 and delta N-15 profiles in teeth from stranded carcasses near age 2 indicated the most probable weaning age. First and second year annual calf survival estimates were 0.84 (95 % CI 0.72-0.90) and 0.86 (95 % CI 0.74-0.94), respectively. No evidence was found to support that timing of birth plays a role in calf survival, suggesting that variability in water temperature and food resources within the year is unlikely to impact upon survival of calves. Older females reproduced at lower rates, suggesting an age-related decrease in reproductive fitness. At an individual level, marked variation in reproductive success was observed. Our findings highlight the importance of long-term studies for long-lived mammals to yield individual- and population-level parameters for demographic and viability analyses that are useful for conservation and management.