Planning for dolphin, shellfish and future fish management

Marine scientists are calling for more focused management strategies and further interventions to secure the future of marine ecosystems and key fish species, as well as “near threatened” dolphins and shellfish species around South Australia’s coastline.

With ongoing pressure from human activities and climate change, three new research articles led by Flinders University experts have warned of the need for more research and regular monitoring to take into consideration rising pressure on marine ecosystems.

Leading South Australian Whale & Dolphin Conservation scientist Dr. Mike Bossley and his team have been tracking the local Indo-Pacific bottlenose dolphins (Tursiops aduncus) of the Adelaide Dolphin Sanctuary for 34 years.

Despite living in this highly urbanized estuary, these dolphins have shown remarkable resilience, say Flinders University researchers in a recent article titled “Long-term demographic trends of near threatened coastal dolphins living in an urban estuary,” published in Ecology and Evolution.

The Flinders University Cetacean Ecology, Behavior and Evolution Lab (CEBEL) study of Dr. Bossley’s long-term data highlighted a troubling population decline between 2012 and 2020.

Fortunately, recent dolphin sightings have stabilized in 2021–24, according to Dr. Bossley’s observations.

“Despite numerous environmental and anthropogenic disturbances, the Adelaide Dolphin Sanctuary is a shallow, protected area and it’s likely that the dolphins are continuing to use this area for its benefits,” says Kennadie Haigh, a Ph.D. candidate at the Flinders College of Science and Engineering.

“It’s important to focus conservation strategies on improving the Adelaide Dolphin Sanctuary ecosystem and promoting connectivity to the surrounding waters to help secure the future of these dolphins.”

The Adelaide Dolphin Sanctuary is located in Port Adelaide and was established in 2005 with the intention to protect the dolphins and the habitat that sustains them.

In addition, a second Flinders University study, published in Ocean & Coastal Management, examined the historical exploitation of South Australian shellfish reefs—and calls for urgent interventions to restore native marine species for local ecosystem health.

“Human and environmental stresses, as well as overfishing and dredge harvesting, have combined to significantly diminish our local multi-species shellfish reefs, which once covered more than 2,600 square kilometers of the state’s coastline,” says Ph.D. candidate Brad Martin.

“Based on historical records, we documented 140 potential shellfish reef locations, and we estimate that more than 43 million flat oysters were commercially harvested statewide between 1849 and 1915, prior to their functional extinction by the 1940s.

“Shellfish reef decline was also influenced by environmental factors including drought and salinity issues, disease, heavy predation by marine species and sediment deposition from storms.”

Researchers say the demise of these coastal features since colonization should be reflected in future conservation and restoration efforts, to include these important native shellfish species in policy-setting and coastal management strategies.

In a third article, published in Environmental DNA, scientists at Flinders University and South Australia’s Department of Environment and Water conducted a study in collaboration with Parks Australia to assess the best method to detect fish communities in marine ecosystems, including remote regions of the Great Australian Bight.

Environmental DNA (eDNA) and Baited Remote Underwater Video Systems (BRUVS) were assessed and compared across offshore seamounts and islands in SA’s Nuyts Archipelago marine park and the Commonwealth South West Marine Park Network.

“Fish communities are critical indicators of ecosystem health, and comprehensive monitoring strategies are vital to effective management of marine fishes,” say Flinders University senior author Dr. Michael Doane.

The study found that two survey methods were effective and complementary in detecting different fish species.

“By combining both methods, we gain a much fuller picture of fish communities,” says first author Ewan Burns. “eDNA excelled at detecting large pelagic species like white sharks (Carcharodon carcharias) and southern bluefin tuna (Thunnus maccoyii), while BRUVS revealed more bottom-dwelling fish,” he says.

This dual approach is particularly valuable in remote, challenging environments like the Great Australian Bight, where it enables monitoring of key species—both those of conservation concern with high economic value—while providing crucial insights into reef health, researchers add.