Fin Identification of the Burrunan Dolphin (Tursiops australis) in Port Phillip Bay: Bridging the Gap to Current Population Assessments

The longevity of marine mammal species worldwide is of significant concern, with 36% already listed as ‘Threatened’. Resident populations adjacent to human centers are particularly vulnerable to anthropogenic pressures,... [ view full abstract ]

The longevity of marine mammal species worldwide is of significant concern, with 36% already listed as ‘Threatened’. Resident populations adjacent to human centers are particularly vulnerable to anthropogenic pressures, particularly high trophic level predators. The newly described Burrunan dolphin, Tursiops australis, is endemic to southern Australia and is characterised by small and isolated populations. There are currently only two known resident populations, Port Phillip Bay (PPB) and the Gippsland Lakes. PPB has an estimated population size of 80 to 100 animals and has an effective population size of 80. Given their low abundance, limited home range, and low genetic diversity, the Burrunan has been listed as ‘Threatened’ under Victoria’s FFG Act 1988, however the conservation status of the Burrunan is yet to be addressed internationally. Opportunistic photo-identification data was collected over 38 boat-based surveys in PPB across multiple years (2006 - 2011). All data was pooled and a total of 82 individuals were identified based on markings along the trailing edge of the dorsal fin, of which 68% (n = 56) were sighted 2 or more times across all sampling occasions. The discovery curve plateaued in 2008, with no new identifications across 4 sampling occasions, followed by a spike in 2011 with 11 new individuals identified across 2 sampling occasions. Results indicate that the population was not saturated across the multiple sampling years. In 2015, we will use photo-identification and capture-recapture methods to assess the current population demographics of the Burrunan dolphin in PPB. Historical data will be used as a baseline to identify variations in population size, and to assess calving rates, site fidelity, and seasonal migration patterns. Population modeling will be applied to data collected in 2015 to produce robust estimates for abundance required to assess the conservation status of the Burrunan dolphin against the IUCN Red List and EPBC Act 1999. Using this information we can address the current data deficiencies and make recommendations regarding future management and conservation of the Burrunan dolphin.