MARCH Meeting 2017

A large audience of members and visitors turned out for our March meeting to listen to guest speaker Delphine Chabanne, a PhD Candidate at Murdoch University’s Cetacean Research Unit (MUCRU), who presented a talk on her PhD project. Delphine is conducting a comprehensive investigation into the ecology and population structure of dolphins inhabiting the coastal waters between Scarborough and Rockingham and the estuarine waters of the Swan Canning Riverpark. To start her presentation she provided some background information on Indo-Pacific Dolphins. The Indo-Pacific Dolphin, Tursiops aduncus, is a cetacean, a toothed whale in the family Delphinadae (Oceanic Dolphin). They have a wide distribution, inhabiting coastal waters around the Indian Ocean. The dolphins have a lifespan of 40+ years for females and 35+ years for males. An adult dolphin weighs around 230kg, with females giving birth to calves weighing between 9 and 21kg. Sexual maturity is reached at 10 – 12 years with females giving birth every 3 to 5 years after reaching the reproductive age. They are highly intelligent, evident from studying dolphin behaviour such as cultural transference – e.g. a tail walking ‘dance craze’ common in South Australia and tool use (they are known to use sponges to forage amongst sharp corals.) Their intelligence is confirmed by brain studies, with a dolphin brain being many times larger than expected for their body size. Dolphins are highly social: males form strong social bonds (alliance); females have large, loose networks; Mother and calf pairs form strongest bonds in the first year after birth. Dolphins employ extreme acoustic specializations: they use echolocation to explore their environment; they emit clicking sounds and listen for echoes; and whistles assist with social cohesion. Their foraging ecology sees them consume a broad diet (mullet, whiting, herring, salmon and cephalopods), which they hunt by employing multiple techniques. Impacts affecting dolphins include stresses caused by habitat destruction, pollution and disturbance (e.g. noise) and interactions with boats and other watercraft as human population increases.

Delphine then moved on to discuss her project, which is part of a broader project, the Coastal and Estuarine Dolphin Project. Delphine’s project is focused on the dolphins of Cockburn Sound. Its aims are to evaluate population size, describe movement of dolphins within the Cockburn Sound, assess social structure and home range and also study the genetics within the population. The fieldwork associated with the project is boat based and involves zigzag transects (from Trig Beach south to Rockingham). The sampling effort involved 4 zones (Cockburn Sound, Owen Anchorage, Swan/Canning and Gage Roads) over 4 austral seasons and five repeats. During the sampling researchers recorded behaviour (whether socialising, travelling, resting or foraging/feeding). A photo identification method is used to identify individual dolphins – each dolphin has a unique dorsal fin, accumulates scars and nicks overtime and sometimes has evidence of bigger trauma such as a boat or shark strike. Good quality data is required. Genetic information is obtained from skin/blubber samples that are collected remotely using the PAXARMS biopsy system (under permit) – a modified .22 rifle fires a biopsy dart and tip. The results of the sampling included sightings of 411 groups over four years, with group size varying from >20 down to 1–5. In Cockburn Sound there were 122 groups sighted. Data on individual sighting frequency was presented that showed that many are resident in Cockburn Sound, others in the Swan/Canning zone and others north of Fremantle. Some individuals were sighted in different zones. A study of the Cockburn Sound dolphins indicated that there are core areas that they frequent and also extended home ranges. A study of dolphin movements found that 83 per cent of individuals in Cockburn Sound are resident and 69 per cent of individuals in Owen Anchorage are resident. Of the Cockburn Sound dolphins 12 per cent will go into the Owen Anchorage zone. These comprise mixed groups of males, females and calves. The zone of interaction is around Woodman Point. Only 2 per cent enter the Swan/Canning zone. The results of genetic studies show that there are some differences in genetic structure between the Cockburn Sound, Swan/Canning, Owen Anchorage and Gage Roads populations but some mixing is evident. Cockburn Sound is a sink population that does not pass genes to other populations; the same applies to the Swan/Canning population. Owen Anchorage is a source population that passes genes to other populations. In summary the project has shown that: the resident population in Cockburn Sound is 65 dolphins; there has been a stable abundance across the years; the dolphins exhibit long site fidelity; and are highly social with stable associations. As far as distribution is concerned there is a hot spot at the Kwinana Shelf, which is used for feeding, resting and caring for calves. The Cockburn Sound population is genetically connected with adjacent sub populations. While answering questions Delphine mentioned that the Kwinana Shelf hot spot is in the vicinity of the proposed Outer Harbour Development. This would be expected to have an adverse impact on the Cockburn Sound population. The audience thanked Delphine for her very interesting presentation.

Colin Prickett