Reproductive parameters of the Taiwanese humpback dolphin (Sousa chinensis taiwanensis)

Reproductive parameters represent an integral component of species' natural history and are essential for well-informed conservation management, but often difficult to access in marine mammals. In this study we estimated the reproductive parameters, including crude birth rate, calf survivorship, annual recruitment rate and calving interval of the Taiwanese humpback dolphin, Sousa chinensis taiwanensis, a critically endangered small population inhabiting inshore waters off the Taiwan west coast. With over 400 boat-surveys completed across five years, 21 mother-calf pairs were individually identified through photographic identification techniques. Births occurred in both warm and cold months, but seemingly decreased in late summer through mid-winter. The reproductive parameter estimates were 0.046 for the crude birth rate, 0.667 for the survival rate to the Age-1, 0.041 for the annual recruitment rate and 3.26 years for the calving interval. Generally, between one and three calves (mean = 2.75) survive annually to the age of 1-year. The low recruitment rate and relatively long calving interval imply a slow population growth and hence limited capacity to resist anthropogenic stress. As the annual recruitment may be lower than current mortality figures, we emphasize the need to re-assess the impact-mitigation baselines and population viability based on these latest reproductive parameter estimates.