Deakin University Edges Closer to Confirming Banjo Shark Nursery in Port Phillip Bay

Deakin University's Groundbreaking Shark Tagging Project in Port Phillip Bay

Researchers at Deakin University's Centre for Integrative Ecology are at the forefront of marine science in Australia, leading a comprehensive study on sharks and rays in Port Phillip Bay. Over the past two years, the team has tagged more than 100 individuals across eight species, including the enigmatic banjo shark, also known as the southern fiddler ray (Trygonorrhina dumerilii). This ovoviviparous species, characterized by its distinctive banjo-shaped body, dark-edged bands radiating from the eyes, and preference for shallow sandy and seagrass habitats, plays a crucial role as a mesopredator in coastal ecosystems. 75 37

The project, part of Deakin's Blue Thread initiative, examines how human activities and climate change influence these species' behaviors and distributions. By attaching acoustic and satellite tags, collecting blood and tissue samples, and using long-line fishing methods, scientists gain insights into movement patterns, residency, and physiological responses. This hands-on approach not only advances knowledge but also trains the next generation of marine biologists through PhD projects and fieldwork opportunities.

Unveiling the Banjo Shark Nursery in Swan Bay

Swan Bay, a marine protected area (MPA) near Queenscliff at the entrance to Port Phillip Bay, has emerged as a prime candidate for the banjo shark's breeding grounds. PhD candidate Louisa Graf, who has focused on this species for two years, reports that tagged juveniles exhibit high residency here, repeatedly returning to the same seagrass meadows. These shallow, nutrient-rich areas provide shelter from predators and abundant prey like crustaceans and small fish, essential for the young rays' growth. 75

Seagrass beds in Swan Bay support over 250 species, underscoring their ecological value. Confirming this nursery status could lead to enhanced protections, demonstrating how university-led research directly informs policy. Graf's work highlights the step-by-step process: tagging small individuals (under 60 cm disc width), monitoring via acoustic receivers, and analyzing residency data to distinguish nurseries from mere foraging sites.

Banjo Shark Biology: From Gestation to Nursery Habits

The southern fiddler ray is endemic to southern Australia, ranging from Western Australia to Bass Strait. Females are ovoviviparous, retaining fertilized eggs internally for up to 12 months due to embryonic diapause—a delayed development phase common in elasmobranchs. Litters of 2-6 pups are born live, typically in spring. Juveniles favor protected bays like Swan Bay for their first years, growing to maturity at around 80-90 cm disc width over 10-12 years. 39 36

• Habitat preference: Sandy flats and Zostera seagrass, depths 1-30 m.
• Diet: Bivalves, polychaetes, crabs—dug up with the snout.
• Threats: Bycatch in trawls, habitat loss from dredging.
• Conservation status: Near Threatened regionally due to historical declines.

Deakin's tagging reveals ontogenetic shifts: juveniles stay put, while adults roam wider, nutrient-transferring across the bay.

Deakin's Research Team and Methodological Innovations

Senior lecturer Samantha Sherman heads the fisheries arm, integrating stressors like shipping, aquaculture, and fishing. Her team employs ethical handling: stabilizing sharks, flushing gills with seawater, and minimizing stress during tagging. Blood samples assess health metrics like stress hormones, while genetics from tissues map populations. 75

This multi-species approach—sevengill (Notorynchus cepedianus), Port Jackson (Heterodontus portusjacksoni), eagle rays—models food web dynamics. Deakin's Centre for Integrative Ecology fosters interdisciplinary work, blending ecology, stats, and policy, ideal for postgraduate training.

Seagrass Meadows: Lifelines for Port Phillip's Marine Nursery

Port Phillip Bay's seagrass (mainly Heterozostera tasmanica) covers 20% of the seabed, vital for nurseries. Swan Bay's meadows buffer juveniles from currents and predators. Yet, warming (1.5°C rise since 1980s) and pollution threaten them. Deakin models predict banjo ray abundance drops by 20-30% without intervention. 0

Restoration efforts, informed by uni research, include planting trials. MPAs like Swan Bay show higher densities, proving efficacy.

Climate Change: Poleward Shifts and Invasion Risks

Australia's southeast coast warms fastest globally (0.13°C/decade). Mesopredators like banjo sharks may contract ranges; models forecast Port Phillip declines. 0 Bull sharks (Carcharhinus leucas), shifting south, could disrupt balances—aggressive, outcompeting locals.

Sherman notes: "The impact would be massive." Deakin's data will nominate refugia.

Human Impacts: Fishing, Poaching, and Habitat Pressures

Bay populations rebounded post-quotas, but illegal fishing in MPAs persists (90% compliance overall). Trawling stresses pregnant females, impacting pups via cortisol spikes. 38 Deakin advocates expanded enforcement.

University Contributions to Marine Policy and Education

Deakin exemplifies Australian unis' role: 70% of marine policy stems from uni research. Programs like MSc Marine Biology train via tagging. PhDs like Graf's bridge science-policy.

• Hands-on fieldwork builds skills in telemetry, stats.
• Collaborations with VFA, Parks Vic.
• Careers: Fisheries officers, conservation NGOs.

Future Outlook: Modeling, MPAs, and Student-Led Conservation

Graf aims to model hotspots, expand MPAs. Deakin's decade-projections guide adaptation. Student involvement fosters careers; e.g., Blue Thread funds diverse researchers.

This research positions Deakin as leader, inspiring higher ed in ecology.

Photo by Craig Wang on Unsplash