Tracking Bottlenose Dolphins in Cockburn Sound

A most interesting case study into the use of remote sensing and GIS relates to ecological research in the behaviour of bottlenose dolphin in Cockburn Sound.

The research was undertaken by Bec Donaldson from the Veterinary and Biomedical Sciences at Murdoch University, in association with Dr Halina Kobryn (Environmental Sciences) and Hugh Finn (Biological Sciences).

Cockburn Sound, situated 12 kilometres south of Fremantle in South West Western Australia bordering a district called “Kwinana”, is 120 kilometres square. Kwinana is one of Western Australia’s main sites for heavy industry. Approximately 200 bottlenose dolphins are resident in Cockburn Sound.

The research project aimed to better understand the ways in which the dolphins were using the sound and their relationships with each other. However, the research also demonstrates some of the ways in which additional information from remote sensing data sets can be used by field biologists to broaden their analyses.

Research was undertaken through 900 boat-based surveys of dolphin groups, during which the observed dolphins were identified (by fin characteristics) and the size, age/sex structure, activities, date/time, presence of fish and GPS locations were recorded.

One research question related to key feeding habitats. The GPS locations of dolphin groups were displayed in ArcView and the data display was integrated with satellite imagery (ACRES LandSat 7, Mosaic of Australia, GeoScience Australia 2003) to identify habitats within the sound. These habitats included the presence of sea-grass, reef, shallow shelves and deep basins.

As the activities of the dolphin groups had been recorded, the researchers were able to identify which activities (mainly feeding, resting, socialising or travelling) occurred in which proportions in each habitat. This showed that dolphin groups spent a significantly higher proportion of time feeding when they were on the shelf than off the shelf.

There is some indication that the shelf area of Cockburn Sound is particularly high in phytoplankton, possibly due to surface run off of nutrients from industry or market gardens along the coast, which forms the basis for a food chain attracting schools of fish that the dolphins then eat.

Links between plankton, fish and dolphins have not been explored yet, but some sampling for surface Chlorophyll a levels have been done and the results overlain with that of the dolphins’ behavioural patterns.

A second component of the research explored the use of different parts of Cockburn Sound by mothers and calves. There is a high proportion of dolphin calves in the sound compared to other populations of dolphins studied elsewhere in the world. The sound is relatively sheltered and, therefore, possibly offers a “nursery” location.

Obviously, dolphin calf survival rates are very important for conservation efforts, and for Cockburn Sound, given the already very small resident population, is particularly important and a higher death rate than that which would occur naturally could lead, in the long term, to extinction of the sub-population.

The research showed that females with young calves, less than one year old, spent more time than expected near the mainland shore, particularly on the shelf. Females with older calves spent more time further from shore. Remember, the shelf area was used predominantly for feeding as well, and the two facts could be due to the increased feeding requirements of females during lactation. It could also be due to defence of the calf against predators. In other dolphin populations, sharks have been shown to take up to 50 per cent of nursing calves. It is possible that the shelf area, being so far from the open water, attracts fewer sharks.

Finally, the researchers used GIS to investigate a social behavioural question relating to the bonds formed by male dolphins.

Males often interact by fighting with each other, particularly during competitions for females. However, in some other dolphin populations around the world, males have been found to form friendly associations with and cooperate with certain other males. No research had been done on whether males showed greater aggression towards males who were close neighbours with much range overlap, or to males whose ranges were further from their own.

GPS locations of each male from field data were displayed in ArcView and polygons were drawn to represent home ranges. Analyses of field data generated proportions of friendly and aggressive interactions between pairs of males. In total, there were 18 males studied.

The results showed that dolphin males that had virtually identical home ranges had 100 per cent friendly interactions. The higher the disparity between the home ranges, the more aggressive the interactions (up to 100 per cent). These findings tie in with some fascinating theory relating to male dolphins. At Shark Bay, males have been found to form small teams or alliances with other males and they often travel together within a shared range, cooperating against rival alliances to compete for females. This behaviour seems to occur at Cockburn Sound as well.

This research has highlighted the possibilities of applying GIS and remote sensing to ecological studies and should greatly assist in conservation management. Better understanding the use of different parts of Cockburn Sound by dolphins, for example, should help in further planning and development decisions in this area. There appears to be an exciting future for the integration of remote sensing and fauna databases in research.

For more information, please contact Dr Halina Kobryn.