Temporal stability of associations in a bottlenose dolphin (Tursiops sp.) population in the western gulf of Shark Bay, Western Australia
Nicholson, K., Pollock, K., Krützen, M., Allen, S., Kopps, A. and Bejder, L. (2013) Temporal stability of associations in a bottlenose dolphin (Tursiops sp.) population in the western gulf of Shark Bay, Western Australia. In: 20th Biennial Conference on the Biology of Marine Mammals, 9 - 13 December, Dunedin, New Zealand.
Previous research indicates distinct differences in the association patterns of male and female bottlenose dolphins (Tursiops sp.) in Shark Bay’s World Heritage Area, Western Australia. In this study, we aimed to quantify these differences and compare temporal association patterns of male and female dolphins. The association data used were collected on boat based photo-identification surveys (n=1356) along ten predetermined transect lines, during each austral winter from 2007 to 2010. Two association indices, half weight (HWI) and simple ratio (SI), were calculated for each pair of individuals observed more than four times during the study. While SI is thought to be the least biased of the two, HWI was also used to ensure meaningful comparisons to other studies. To determine whether the observed associations between individuals differed from that of a randomly associating population, permutation tests were carried out on the association matrix. Lagged association rates (LAR) were also calculated and models describing social organisation fitted to them to investigate the temporal stability of associations in the population. Results showed that individuals in the western gulf of Shark Bay associate non-randomly (p< 0.001). Both males and females tended to mostly associate with individuals of the same sex (Mantel test t=5.428, p< 0.001) and adult males formed stronger and more temporally stable associations with other males than females did with other females (LAR males > LAR females, LAR males > null LAR, LAR females > null LAR). Despite differences in habitats and the lack of population connectivity between study areas, these findings are consistent with previous findings from the eastern gulf of Shark Bay. The methods used in this study are suitable for quantitative analysis of general association patterns in other cetacean populations.
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|Murdoch Affiliation:||School of Veterinary and Life Sciences|
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