True locals make Coffin Bay their home

When dolphins are in a safe, bountiful environment, they don’t venture far – despite having the capability to range over vast ocean distances. And within such areas, we need to ensure that dolphin populations remain protected and secure, with good management.

Flinders University researchers have performed detailed studies of a large dolphin population in Coffin Bay, at the foot of South Australia’s Eyre Peninsula, and found that when dolphins find such a patch of paradise, with high amounts of food to source and low risk from shark interference, they are inclined to stay and make it their home rather than to roam.

Dr Cecilia Passadore, who led the research as part of her PhD studies with the Cetacean Ecology, Behaviour and Evolution Lab (CEBEL) at Biological Sciences (College of Science and Engineering) at Flinders University, says an estimated 300 southern Australian bottlenose dolphins live in Coffin Bay, with a very high density particularly for the inner area of about 1.7 dolphins per square kilometre.

The Flinders team’s recently published research – Passadore, C., Möller, L., Diaz-Aguirre, F., and Parra, G. J. (2017) High site fidelity and restricted ranging patterns in southern Australian bottlenose dolphins. Ecology and Evolution, n/a-n/a. doi: 10.1002/ece3.3674 – identifies that dolphins show strong site fidelity and restricted ranging patterns (usually about 15 square kilometres) within the inner area of Coffin Bay. A large proportion (56%) even restrict their space use to particular embayments within Coffin Bay.

This strong site fidelity to very small areas is rather unusual in highly mobile marine mammals – identifying Coffin Bay as a special site for dolphin population research. Coffin Bay is part of Thorny Passage Marine Park (TPMP), and this research shows it is an excellent starting point for the protection of such a concentrated dolphin population.

Interaction between marine mammals and vessels, as well as tourism operations, are regulated through the National Parks and Wildlife (Protected Animals – Marine Mammals) Regulations 2010, which places restrictions on the distance and speed of vessels approaching dolphins, and restrictions on swimmers and food provisioning. However, Dr Passadore argues that much more could be done.

“Although marine mammals are considered species’ of ecological value in the management plan of TPMP, there are no specific conservation and management measures directed at monitoring or protecting southern Australian bottlenose dolphins,” says Dr Passadore. “We suggest that the potential threats that these dolphins face within this multiple use marine park could be monitored and effectively managed by incorporating the species into TPMP’s management plan.”

The stable population, tracked by Flinders researchers through the past two years, highlights the high conservation value of Coffin Bay for southern Australian bottlenose dolphins – and underlines the care and caution that summer visitors to Coffin Bay must exercise to avoid affecting such a pristine dolphin sanctuary.

“Dolphins in the inner area of Coffin Bay are truly locals,” says Dr Guido Parra, who was one of the research authors. “They don’t venture far from home and most of them actually use particular areas within the bay,” he says.

“Dolphins that have such localised movement patterns are particularly susceptible to localised human pressures that could negatively impact upon them, such as habitat degradation and loss, entanglements in marine debris, interaction with fisheries (such as bycatch or reduction in prey availability due to overfishing) and pollution, among others.”

Therefore, Dr Parra argues that current and future activities and developments, as well as marine parks zoning arrangements in the area, should all consider the local dolphins in their management strategies.

“If you visited Kellidie Bay (an embayment within Coffin Bay) in two different years and both times you saw dolphins, big chances are that both times you encountered the same individuals, which you can recognize by natural marks on their dorsal fins,” says Dr Passadore. “We propose that these patterns of high site fidelity and restricted ranges are likely driven and maintained by the high productivity of this system, with enough year-round food supply to sustain the dolphin population throughout the year, possibly coupled with low predation risk.”

This new research helps to further a better understand of dolphins, with the published research highlighting the importance and conservation value of the inner area of Coffin Bay for southern Australian bottlenose dolphins, and provide the basis for guiding future monitoring and spatial conservation planning of the species within South Australia’s marine parks.

“We’ve just started studying dolphins in Coffin Bay and what we’re able to learn in only two years of data collection is fascinating, and only leads to future goals to investigate,” says Dr Passadore, from CEBEL. “It’s a perfect site for intensive research, with high productivity within Coffin Bay plus low predation risk from sharks being keys for dolphins to decide to stay at home rather than disperse or move broadly. Why go anywhere else when they can be safe and get all of their food right in their backyard.”

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