Abstract: The Port River estuary (Adelaide, South Australia) supports a population of Indo-Pacific bottlenose dolphins (Tursiops aduncus) despite its heavily modified habitat. This paper reports the calving season, birth rate, calf mortality, and inter-birth interval of the resident population, all factors important in the conservation of this population. Between 1989 and 2005, 1,176 boat surveys were undertaken, covering all seasons for each year. All dolphins encountered were photographed, and their location, number, age category, and behaviour were recorded. Dolphin identity was determined a posteriori using photo-identification. Results indicated a calving season from December to March, which coincided with the maximum surface water temperature of the estuary. Inter-birth intervals were consistent with the literature—3.8 y when the previous calf was weaned and 1.7 y when the previous calf died—with the exception of one special case. Forty-five calves were born to resident females between 1989 and 2005, and the average crude birth rate was 0.064, which is similar to that found for other bottlenose dolphin populations. First-year calf mortality (30%) and mortality rate for calves prior to weaning (46%) were higher than mortality rates described for other locations. Minimal predation is thought to occur in the estuary, and there was no evidence of poor condition in the mothers, suggesting that the high mortality rates were caused by direct impacts on calves such as entanglements, boat strikes, deliberate attacks, or exposure to toxic pollution.

Key Words: Indo-Pacific bottlenose dolphin, Tursiops aduncus, inter-birth interval, reproduction, seasonality, birth rate, calf mortality, Port River estuary, Adelaide, South Australia

Document Type: Research article

DOI: 10.1578/AM.34.1.2008.84

Page Numbers: 84-92