Patterns of association among female Indo-Pacific bottlenose dolphins (Tursiops aduncus) in a population forming large groups

Indo-Pacific bottlenose dolphins (Tursiops aduncus) around Amakusa-Shimoshima, Japan form large groups of >100 individuals, a remarkable feature of this population, which is much larger than previously studied bottlenose dolphins. Using photo-identification data collected on 33 days in 2012, associations among 70 females were investigated using two scales of association measure (photograph-and group-based association) to know whether they associate based on their reproductive status, as is typically observed in other populations with smaller group size. Significant differences in associations between females of the same reproductive status category and those in different categories were detected, and a female that lost her calf within a year decreased associations with females with calves of the same age. These suggests that even in a population with large group size, the reproductive status of females is one of the factors influencing their associations.