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Fiddlers and banjos at the bottom of the bay might sound like a sunset cruise gone wrong, but it’s all part of the natural ecosystem. Banjo sharks – also known as southern fiddler rays – are prosperous and plentiful across Port Phillip Bay and beyond. And, although we already know a good deal about these gentle creatures, there are still some big pieces of the puzzle missing.
This is where Deakin graduate researcher Louisa Graf comes in.
As one of Deakin’s next generation of marine scientists, Graf is dedicating her research to learning more about how banjo sharks impact our temperate marine ecosystem, and how this may change depending on their life stage and season.
We’ve introduced two key terms or ‘names’ already: the southern fiddler ray and the banjo shark.So, what is a southern fiddler ray, and what is a banjo shark?
As Graf explains, they’re actually the same thing; the names are interchangeable.
‘They are the same species,’ she says. ‘They’re globally recognised as the southern fiddler ray and locally known as the banjo shark in Victoria.’
Don’t let the name fool you, though – banjo sharks aren’t really sharks.
‘Much to people’s surprise, they are not a shark, and they are not a stingray – they are a ray,’ says Graf. ‘The banjo shark belongs to a group referred to as “shark-like rays”, hence the shark/ray confusion.’
Graf says that, as with other rays, southern fiddler rays/banjo sharks are ‘dorsoventrally flattened’ (which means their bodies are flat parallel to the ground) but, unlike stingrays, they lack a barb or a stinger.
‘Instead, they have prominent dorsal fins, giving them a more shark-like appearance,’ Graf says. ‘Their body shape also resembles a banjo, which is how they got their name. They are also characterised by distinctive, ripple-like patterns across their backs.
If the banjo shark is actually a ray, and not a shark, then what’s actually the difference between sharks and rays? As Graf explains, the biology of these sharks and rays makes them both cartilaginous fish, but have some key differences.
‘Sharks are typically streamlined, torpedo shaped, with gill slits on the sides and pectoral fins separate from their head, whereas rays are dorsoventrally flattened, with gill slits underneath their body and pectoral fins fused to their head, forming a disc-like shape,’ she says. ‘Differentiating between a shark or a ray lies in the location of their gill slits and pectoral fins.’
Despite the technicalities, though, the banjo shark name seems to have stuck – here in Victoria, at least. Elsewhere, southern fiddler ray is a common name.
As part of Deakin’s marine graduate research team, Graf is keen to explore the role of banjo sharks in our local ecosystem. Her research will expand on what we already know about the banjo shark’s importance – and they are certainly important.
Banjo sharks are a type of predatory animal known as a ‘mesopredator’. This means that they are not the apex predator of their ecosystem (they can actually be prey themselves), but they’re still a key predator when it comes to maintaining the balance of the food web. In this sense, they provide an important link in the food chain for both larger predatory species and smaller prey.
As Graf explains, banjo sharks are also vitally important to their local ecology, too, helping to ‘maintain ecosystem function.’
‘When rays forage for food, they flap their wings and dig into the sediment, this cycles the benthic nutrients into the water column, providing food for smaller animals, releasing nutrients trapped in sediments, and creating microhabitats from the feeding pits they create,’ Graf says.
Port Phillip Bay is one of the most important banjo shark/southern fiddler ray areas, but Graf hopes her research can explore new horizons by tracking banjo sharks as they move through the bay.
‘We track these animals using an underwater tracking technology called acoustic telemetry,’ Graf says. ‘To track these animals, we tag them with trackers no larger than your index finger. These tags can last up to ten years, and we then release the animal back into the water.
Once the animals are tagged, Graf says that she can track them as they pass near underwater listening stations, which are placed both in the bay and further afield along the coast.
‘When a tagged ray swims within range of one of these underwater listening stations, their tag will ping. When we then go and collect that station, we can download the data and see which animals have been nearby. From this, we can track their movements. We are starting to see some seasonal patterns in their behaviour, as well as some differences in movements and space use between the juvenile and mature rays. Once we download more data, we will be able to map this.’
Beyond tracking banjo sharks’ movements, Graf is also closely exploring their diets as part of her PhD. Using some sophisticated analysis, Graf hopes to fill in the blanks of what we already know about what and how southern fiddler rays eat.
‘I am using biochemical analyses (stable isotopes and fatty acids) to get a better idea about what they eat, if this changes seasonally or across life stages,’ she says. ‘At the moment, from previous research, we know that broadly, they like to feed on small marine crustaceans such as shrimp and crabs, and some demersal fishes.’
For Louisa Graf, learning more about how banjo sharks/southern fiddler rays habitate, eat and move is just the beginning. Through her PhD, she hopes to contribute to our understanding of not only this important species, but Australia’s sharks and rays more generally.
‘My research is part of a bigger puzzle that we are trying to piece together here in Victoria,’ she says. ‘That is, what are our local sharks and rays doing? How do they share space and resources? We don’t know this in Victoria. My research can also be important for conservation and management purposes, as a lot of my tracking happens in a Marine Protected Area. If I can show that these animals are thriving in this area, then that is important for future considerations on how to conserve our local sharks and rays, as our oceans continue to be impacted by climate change.’
While her PhD continues, it’s fair to say that having the support of a dedicated researcher like Lousia Graf should be music to the ears of banjo sharks and fiddler rays everywhere.
Graduate researcher
Deakin University
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