Guardians of the Bay: Unravelling the Secrets of Port Phillip’s Sharks and Rays
The vast expanse of Port Phillip Bay, a jewel in Victoria’s coastline, is a complex ecosystem teeming with life. While often perceived as a playground for human recreation, it’s also a vital habitat for a diverse array of marine species, including a significant population of sharks and rays. However, these often-misunderstood creatures are facing mounting pressures from human activities and the relentless march of climate change. Researchers from Deakin University are on the front lines, working tirelessly to understand and protect these crucial inhabitants of our marine environment.
The Delicate Art of Scientific Study
Imagine the scene: a two-metre sevengill shark, a powerful creature of the deep, is carefully manoeuvred from the water onto the deck of a research vessel in Port Phillip Bay. It’s not a simple task. Three dedicated researchers work in unison, their movements precise and deliberate. They maintain a firm grip, ensuring the shark’s powerful jaws remain safely closed while stabilising its wriggling form. As the animal is held, a vital process unfolds: researchers funnel water through its gills, ensuring its continued well-being. Swiftly, a tracking device is implanted beneath its tough, leathery skin, and crucial blood and tissue samples are collected. This meticulous process, carried out with the utmost care, is repeated for approximately 100 sharks and rays over the past two years.
This intensive tagging program is the cornerstone of a comprehensive study by Deakin University, aiming to assess the multifaceted impacts of human activities and a changing climate on these species within Melbourne’s iconic bay. “We’re not just looking at fishing, we’re also looking at the shipping channels and the abalone farms and how all those stressors might affect sharks and rays,” explains Samantha Sherman, a senior lecturer in fisheries.
Beyond the Apex Predator Myth
Contrary to popular belief, the sharks and rays inhabiting Port Phillip Bay are not the apex predators that many might assume. Dr. Sherman clarifies that they are, in fact, mesopredators. This means they occupy a middle ground in the marine food web, preying on smaller marine animals while themselves being vulnerable to larger predators. “We look at the species which are the ones in the middle of the food web, some of the smaller sharks like the Port Jackson and some of the rays like the banjo sharks and Melbourne skate,” she elaborates.
For decades, experts have observed a concerning decline in shark and ray populations. However, there is a glimmer of hope. Since the ban on commercial net fishing was implemented in 2022, researchers are beginning to see signs of population recovery.
A Vital Nursery Discovered: Swan Bay’s Hidden Promise
Nestled near the entrance of Port Phillip Bay lies Swan Bay, a tranquil sanctuary near Queenscliff. This area is believed by Deakin University PhD researcher Louisa Graf to be a crucial nursery ground for banjo sharks, also known as fiddler rays, and other young marine species. “What we are starting to see is that the juveniles are more resident within Swan Bay which may indicate they are using it as a nursery,” Ms. Graf states, her voice filled with scientific optimism.
Ms. Graf has been diligently tracking 60 banjo sharks she has tagged, aiming to understand their reliance on Swan Bay and how their behaviour evolves throughout their life stages. The bay’s floor is carpeted with lush seagrass meadows, providing a habitat for over 250 different animal species, according to the Swan Bay Environment Association.
“In order to have an important nursery we need to make sure that the marine ecosystem is working well,” Ms. Graf stresses. “The southern Australian coastline is really at risk — it’s a global hotspot for ocean warming so we need to make sure we understand how the sharks and rays are using this area now. Then we can implement management protocols to ensure they can be safe in the future.”
Swan Bay already benefits from fishing restrictions in certain areas, designated as a Marine Protected Area (MPA). These MPAs are specifically designed to safeguard biodiversity by limiting human activities. “MPAs are a brilliant management tool for sharks and rays and if we can continue to show that they are successful then maybe we can designate more along the coastline,” Ms. Graf suggests.
A Holistic Ecosystem Approach
The banjo shark is just one of eight species that the Deakin University team is monitoring in Port Phillip Bay. This broader research initiative aims to provide a comprehensive understanding of the movements and patterns of the bay’s entire shark and ray population. Dr. Sherman underscores the importance of this holistic approach, explaining that focusing solely on individual species can be misleading. The decline of one species may not be catastrophic if other healthy populations can fill its ecological niche.
“Sharks and rays play really important roles in our ecosystems, they’re responsible for moving nutrients around because they’re bigger than a lot of fish so they move further distances,” she explains. “They also can be prey to some larger animals like the larger sharks, but they also consume some of the smaller animals so they can keep that balance in the ecosystem.”
Dr. Sherman highlights the unique characteristics of Port Phillip Bay: it is both large and shallow, with a densely populated coastline. “It’s a system that’s unlike others in the world so we don’t have others that we can use to understand what’s going on here,” she points out, emphasising the critical need for localised research.
Climate Change: A Shifting Tide
The global phenomenon of climate change is undeniably altering marine ecosystems, pushing species towards cooler, more polar waters. Dr. Sherman notes that scientists are already observing significant shifts. The sighting of a bull shark in eastern Victoria in 2024 is a prime example, likely driven by changing ocean currents and temperatures.
“If they keep moving southward eventually, they’ll be in Port Phillip Bay and the impact they would have on the ecosystem would be massive because the species we have here would not be able to outcompete the bull sharks,” Dr. Sherman warns. “So even though their populations are fine and not threatened by fishing, they may become threatened by other species moving further south in the future.”
The warming waters present a stark choice for marine life: adapt, relocate, or face the grim reality of extinction. However, Ms. Graf believes the data being meticulously collected from the bay’s tagged sharks and rays can be instrumental in modelling these distribution changes over the coming decades.
“Then we can nominate hotspots or decreases in abundance along the coastline,” she says. “Then we can use that [data] to designate, well this is an important area for sharks and rays, this one isn’t as important, are there any MPAs in those hotspots of abundance and maybe there should be,” Ms. Graf concludes.
The Challenge of Enforcement
Despite the scientific efforts, researchers have noted an increase in illegal activities, particularly since funding cuts to the Victorian Fishing Authority. The authority has reportedly reduced the number of legal enforcement officers, replacing them with fewer engagement officers to patrol state waters. “There’s very little monitoring … we are seeing that people are poaching within the marine protected areas,” Dr. Sherman states with concern.
In response, a Victorian government spokesperson confirmed the establishment of the Major Fisheries Crime Unit, tasked with combating organised illegal fishing operations. The spokesperson also reassured the public, stating, “Most people in the fishing community are doing the right thing — there is 90 per cent compliance with fishing rules and regulations.”
The ongoing research in Port Phillip Bay is not merely an academic exercise; it’s a critical endeavour to safeguard the future of these vital marine mesopredators and the health of the bay’s unique ecosystem in the face of unprecedented environmental challenges.
