Social alliances play a key role in the success and survival of group-living mammals. Investigating the occurrence and stability of social alliances through time and space are informative of network drivers.

Social interactions among mammals are known to influence a range of essential life processes including offspring survival, reproductive success, and longevity through protection from predators and resource acquisition. Dolphins are highly social animals, forming some of the most complex social structures known, from fission-fusion societies through to strong, long-term social bonds. For females, these bonds usually occur between kin (mother-calf associations) forming nursery groups with other females of the same status as a protective/shared care maternal strategy to enhance their offspring’s survival. In contrast, males are known to form strong alliances with other males to enhance their reproductive opportunities. However, a number of social, demographic and ecological factors are known to influence social interactions, thus social networks are context-dependent and can provide great insight into drivers of population structure.

We are currently conducting research about the social network structure within both the Port Phillip Bay and Gippsland Lakes populations.

Port Phillip Bay:

Using robust and established methods to quantify and assess social structure based on photographic fin-identification, we aim to investigate associations among individually identifiable Burrunan dolphins to;

1. Determine social network structure of the Port Philip Bay population

2. Investigate changes to social network structure over space and time

3. Identify the possible drivers of social network structure, thus the evolutionary adaptations of the population

Understanding the social network structure of the PPB population will be critical for the ongoing conservation of the small, genetically distinct and isolated population inhabiting one of the most heavily urbanised coastal/inshore environments in Australia.

Gippsland Lakes:

In contrast to the Port Phillip Bay population, resident Burrunan dolphins in the Gippsland lakes have a unique social system, influenced by an atypical winter breeding season. Despite being in relatively close proximity to Port Phillip Bay, these populations are isolated with minimal migration occurring between them, based on genetic structure and diversity (Charlton-Robb et al. 2016). Preliminary social analyses suggests these populations exhibit markedly different social network structures, which could be driven by a number of ecological, social and demographic factors unique to each population. Unlike the PPB population where both males and females remain within their natal range in adulthood, the GL population is maternal-based, meaning the majority of the population are females except during their unique winter breeding season (most Tursiops spp. have summer breeding seasons) when an influx of males entering the lakes from the south-eastern coast of Tasmania in austral winter. There are numerous differences between the population, which provide an exciting opportunity to explore the GL social structure and compare with the PPB population, determining drivers of social cohesion within the population and in doing so, provide an explanation of potential fitness benefits, thus evolutionary adaptations of the populations.

Using robust and established methods to quantify and assess social structure based on photographic fin-identification, we aim to investigate associations among individually identifiable Burrunan dolphins to;

1. Determine social network structure of Gippsland Lakes population

2. Investigate changes to social network structure over space and time

3. Identify the possible drivers of social network structure, thus the evolutionary adaptations of the population

If you would like to help us get on the water and continue to conduct our research, consider a donation! As a small not-for-profit organisation, every little bit goes a long way.

Presentations

• Sondermeyer, N., Arnould, J., Charlton-Robb, K. (2017) Investigating the population structure and social alliances of Tursiops australis in Port Phillip Bay. Poster Presentation. 22nd Biennial Conference on the Biology of Marine Mammals. Halifax, Canada.

• Sondermeyer, N., Arnould, J., Charlton-Robb, K. (2017) Investigating the population structure and social alliances of Tursiops australis in Port Phillip Bay. Oral presentation. Victorian Biodiversity Conference. Melbourne.