SIMS

The Marine Mammal Research Group at Macquarie University has had great success with a number of staff and students who have studied human impacts on bottlenose dolphin populations around Jervis Bay and Port Stephens.

In a very recent study published in the international journal Biological Conservation, PhD student Michelle Lemon found that the presence of commercial and recreational powerboats in areas where dolphins are swimming has a significant effect on how the dolphins behave on the water’s surface and on the direction that they swim.

Lemon and her colleagues recorded the surface and acoustic behaviour of groups of bottlenose dolphins travelling in Jervis Bay on the NSW south coast. Using a series of controlled approaches by a powerboat similar to other recreational and commercial watercraft found in the area, the dolphins’ reaction was monitored before the boat approached, while it was near the group for a period of time and after it left the area.

They found that dolphin groups changed their surface behaviour from travelling to milling, which is generally a transition behaviour. Further, when travelling, the dolphins changed their direction, orienting themselves away from the approaching powerboat. Importantly, changes in the dolphins’ behaviour occurred even before the powerboat came within the 30 metre minimum approach distance proposed by the NSW National Parks and Wildlife Service for recreational and commercial boats.

At the current time, there are approximately 120 resident and transient bottlenose dolphin inhabitants of Jervis Bay. Lemon, who also conducts research in Port Stephens on the NSW central coast, says that because there were significant behavioral changes seen observed in dolphins with only one powerboat present, it is clear that further long-term studies on the cumulative effects of more than one powerboat are necessary.

Other genetic research undertaken by Dr Luciana Moller and Dr Luciano Beheregaray is helping us to understand how bottlenose dolphins disperse in the wild and how they form social networks.

Their analysis found that most male bottlenose dolphins in Port Stephens and Jervis Bay were not related closely to the rest of the group, and therefore had migrated from the area in which they were born. There was a much higher percentage of relatedness amongst the females in each population, however, suggesting that they were mostly from the local area. It is believed that females benefit more than males from familiar food sources, and that large bands of related females may help protect the individuals, and their calves, from predators and males.

The findings put to rest a long-running debate over kinship within dolphin communities.

“Based on behavioral observations in Shark Bay, Western Australia, and Sarasota Bay, Florida, researchers thought that both females and males must stay in their local geographic area during their lives,” Moller says. “This would be very unusual behavior for a mammal, however, as usually males disperse in order to minimise inbreeding and competition for food and females amongst relatives.”