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Sex-specific patterns in abundance, home ranges and habitat use of Indo-Pacific bottlenose dolphins (Tursiops aduncus) in south-western Australia

Sprogis, Kate (2015) Sex-specific patterns in abundance, home ranges and habitat use of Indo-Pacific bottlenose dolphins (Tursiops aduncus) in south-western Australia. PhD thesis, Murdoch University.

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This thesis explores sex-specific patterns in population abundance, demographic parameters, home range size and habitat use by Indo-Pacific bottlenose dolphins (Tursiops aduncus) off Bunbury, Western Australia. Photographic-identification data were collected year round between 2007-2013 through systematic boat-based surveys along pre-determined transect lines within a 540 km2 study area consisting of open coastal waters and sheltered waters. Chapter one provides background and outlines the specific aims of the thesis. In Chapter two, I estimated sex-specific population parameters of abundance, movement and survival using Pollock’s Robust Design. The estimated number of dolphins in the study area was seasonally dependent, and for identifiable adult males ranged from 24 (± 5.73 SE) to 50 (± 5.48 SE) and for identifiable adult females from 28 (± 2.99 SE) to 60 (± 2.38 SE). The lowest abundance estimates coincided with both the strongest phase of an El Niño event and an unparalleled peak in dolphins temporarily emigrating out of the study area. In Chapter three, I explored sex-specific differences in home range size using a new approach for kernel density estimation that accounts for physical barriers to movements. A Bayesian mixture model indicated a 99% probability that adult males have larger home ranges than females (adult males 27-187 km2 and adult females 20-133 km2), and that dolphins sighted primarily in open waters have larger home ranges than those residing in sheltered waters. In Chapter four, I used kernel density analyses and generalised additive models to explore seasonal space use and elucidate biotic and abiotic variables that influence seasonal habitat use differences between the sexes. I documented differing variables influencing habitat use between sexes and seasons, high use areas within the bay during summer, movements offshore and a concentration of females in the estuary during winter. I discuss factors that may explain the documented sex-specific differences in abundance, demographic parameters, home ranges and habitat use, including intrinsic (social dynamics, dolphin biology) and extrinsic (prey availability, predation risk, environmental variability) factors. My research emphasises the value and importance of a sex-specific approach when studying the behavioural ecology of coastal delphinids.

Publication Type: Thesis (PhD)
Murdoch Affiliation: School of Veterinary and Life Sciences
Supervisor: Bejder, Lars, Kobryn, Halina, Pollock, Ken and Wells, Randall
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