Omari Gates
Shark populations in Australia have been declining over the past few decades due to a variety of factors. Despite shark attacks in Australia attracting a lot of attention, they are still considered uncommon, and the risk of a fatality from a shark attack remains low. The causes of the decline in shark populations are varied, but primarily include overfishing, habitat loss, and climate change. Research has shown that shark populations are highly vulnerable to exploitation, with commercial and recreational fishing pressure being a key factor in the decline. Additionally, factors such as an increase in the human population along coastal areas, more people visiting beaches, and the rise in popularity of water-based activities have also contributed to the decline in shark populations.
| Characteristics | Values |
|---|---|
| Reason for decrease in shark population | Overexploitation of large apex marine predators, overfishing, habitat loss, climate change |
| Percentage decrease in shark population | 74-92% |
| Shark species affected | Hammerhead, whaler, tiger shark, white shark |
| Human impact | Direct and indirect |
| Impact on the ecosystem | Loss of resilience and health of Australian coastlines, overgrazing of marine vegetation |
| Conservation efforts | Protection of shark populations and their roles in ecosystems, establishment of marine protected areas and fishing restrictions |
| Data sources | Shark control program data, historical records of shark captures, research studies |
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What You'll Learn
Overfishing
The University of Miami (UM) Rosenstiel School of Marine and Atmospheric Science's research provides a stark example of the impact of commercial shark fishing. They studied two neighbouring coral reef systems off the coast of northwestern Australia: Rowley Shoals, a marine reserve protected from fishing, and Scott Reefs, which has been subjected to centuries of commercial shark fishing. The results were telling, with healthy shark populations at Rowley Shoals and decimated populations at Scott Reefs.
In addition to the direct removal of sharks from their ecosystems, overfishing has also led to indirect impacts on shark populations. For instance, the removal of apex sharks can change the structure of coastal food webs, as reef fish may alter their feeding behaviour to seem less appealing to predators. This can lead to a decrease in the energy-rich food they consume, resulting in leaner fish.
Furthermore, overfishing has contributed to the concurrent declines in the body size of large coastal apex sharks in Australia. Research has shown that the average size of sharks, specifically tiger sharks and hammerhead sharks, has decreased over time. This suggests that shark populations are highly vulnerable to exploitation, and their recovery may be challenging.
The Australian Institute of Marine Science (AIMS) has also reported that shark populations in Western Australia are doing relatively well in isolated reefs with marine protected areas that have prevented fishing for decades. These findings highlight the importance of implementing effective fishing restrictions and conservation measures to protect shark populations in Australian waters.
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Climate change
The impact of climate change on shark populations is evident in the decline of large coastal apex sharks in Australia over the past five decades. Studies have reported a 74-92% decline in the catch per unit effort of hammerhead, whaler, tiger shark, and white shark species. This decline is attributed to the vulnerability of apex shark populations to exploitation, with concurrent declines in body size and the likelihood of encountering mature individuals.
The combination of climate change and overfishing has altered the distribution of sharks in Australia. For example, tiger sharks are being drawn further south along the coastline, while bull sharks are lingering in Sydney's Harbour year-round.
Additionally, the impact of climate change on shark populations extends beyond their numbers and distribution. It also affects their physical characteristics. Studies have reported concurrent declines in the body size of large coastal apex sharks, indicating that the average size of sharks is also decreasing.
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Water-based activities
Surfers are more prevalent in the data on shark bites than swimmers or waders, experiencing 42% of the 69 unprovoked bites worldwide, 22% of which occurred in Australia. Swimming or surfing alone or far from major towns or cities increases the chances of a shark bite. This is because, in less populated areas, a person is more likely to be the only one in the water, and if a shark takes an inquisitive bite, they are more likely to bleed out before receiving help.
The increase in shark bites is not due to an increase in shark numbers, as there is evidence that at least some shark populations in Australia have declined. This decline has been influenced by commercial and recreational fishing pressure, shark nets and drum lines, and environmental factors such as variations in water temperature, reduced water clarity, and climate change.
The overexploitation of large apex marine predators is widespread in Australian oceans, with a 74-92% decline in the catch per unit effort of hammerhead, whaler, tiger, and white sharks over the past five decades. This decline has also been reflected in the concurrent declines in the body size of these sharks, indicating their vulnerability to exploitation.
The way that people use the ocean has changed, with an increase in water-based activities and a rise in the human population, which has contributed to the increase in shark bites in Australia.
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Population density
The higher population density in these coastal areas leads to an increased human presence in the ocean, with more people engaging in water-based activities such as surfing, diving, and swimming. This heightened human-shark interaction potentially contributes to the perception of an increase in shark attacks. However, it is essential to note that the actual number of shark attacks remains relatively low, with an average of 6.5 incidents per year in the 1990s and 2000s, rising to 15 incidents per year in the following decade.
The population density of sharks along the Australian coastline is also a factor. The coastal shark population, particularly in Queensland, has been declining over the past five decades, with large apex sharks experiencing a 74-92% decrease. This decline is attributed to factors such as overfishing, shark nets and drum lines, and habitat loss. The commercial and recreational fishing industry has exerted significant pressure on shark populations, particularly in Queensland.
The higher population density in coastal areas can also influence the distribution of sharks. For example, the deadly tiger shark may be drawn further south along the coastline, while the bull shark may linger in Sydney's Harbour year-round. These changes in distribution can impact the likelihood of shark encounters and potentially affect the perception of shark population density in certain regions.
Additionally, the vastness of Australia's coastline means that individuals engaging in water activities may find themselves isolated, increasing the risk of a shark bite. Culum Brown, an associate professor of biological sciences, notes that being alone in the water enhances the chances of a shark bite. This isolation is more common in Australia compared to countries like the US, where beaches are typically crowded.
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Shark nets and drum lines
Shark Nets
Shark nets are submerged along popular coastlines and allow sharks to swim over or around them. They do not create a barrier for people to enter the water, and they barely cover half the depth of the water they are set in. Shark nets also threaten non-target marine animals, such as dolphins, turtles, and even whales. Since the introduction of shark nets, thousands of protected sharks have died along Australia's shorelines.
Drum Lines
Drum lines are large baited hooks attached to chains and a buoy to attract sharks. They are unmanned aquatic traps used to lure and capture large sharks. Drum lines physically attract sharks from within the immediate vicinity, and animals caught on these hooks, including undersized sharks and non-target species, can suffer for hours before being discovered by patrols. Drum lines have been used with success in reducing shark attacks in some areas, such as Recife, Brazil, where the shark attack rate dropped by 97%.
SMART Drum Lines
SMART drum lines can be used to move sharks, which reduces shark and bycatch mortality. Between 2 December 2015 and 9 September 2018, SMART drum lines were used to intercept, tag, and relocate 370 dangerous sharks, including 300 White Sharks, 43 Tiger Sharks, and 27 Bull Sharks. The tagged sharks moved away from the coast for an average of 74 days before being detected again. This provides confidence that SMART drum lines are effective in removing the immediate risk to beach users.
While the combination of drum lines and shark nets may not directly lead to extinction, they can hinder the population's ability to recover from being endangered. Drum lines have been criticized for resulting in the death of thousands of sharks and other wildlife, and some experts have warned that these measures will only further dwindle the numbers of threatened and endangered species. The Australian Marine Conservation Society expressed concern, stating that 97% of sharks caught in Queensland since 2001 were considered to be at some level of conservation risk.
The use of shark nets and drum lines has been cited as a contributing factor to the decline of shark populations in New South Wales and Queensland.
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Frequently asked questions
There are several factors that have contributed to the decline in shark populations in Australia. Some of the main reasons include:
- Overfishing and commercial fishing pressure: The overexploitation of large apex marine predators, such as hammerhead, whaler, tiger, and white sharks, has led to a significant decline in their populations.
- Habitat loss and climate change: Warmer waters are forcing sharks to migrate to different habitats, and climate change can also contribute to variations in water temperature and reduced water clarity, affecting shark behaviour.
- Shark control and protection programs: While these programs aim to reduce shark attacks, they have also inadvertently contributed to the decline in shark populations, especially in New South Wales and Queensland.
- Environmental factors: The increase in human population along coastal areas and the rise in water-based activities have changed the way people interact with the ocean, potentially impacting shark behaviour and contributing to the perceived increase in shark attacks.
- Water-based activities: An increase in activities such as surfing and diving can increase the chances of shark encounters and potential attacks.
It is important to note that while shark attacks attract a lot of attention, they are still relatively rare in Australia, and the risk of a fatality from a shark attack remains low.
No, the declines are not consistent across the country. Some areas, such as the Rowley Shoals in Western Australia, have healthy shark populations due to effective marine protection and fishing restrictions.
Sharks play a pivotal role in maintaining ecosystem diversity, resilience, and health along Australian coastlines. The decline in shark populations can have cascading effects on the coastal food webs and the health of marine vegetation like seagrass beds.
Yes, since 2021, Australian authorities have been working to change public perception and garner support for conservation efforts. Additionally, marine protected areas and fishing restrictions have been implemented in some regions to protect shark populations.
The removal of apex sharks from ecosystems can cause behavioural changes in other marine species, such as reef fishes. This can lead to alterations in feeding patterns and body shapes, as observed in some studies.
The timing and extent of shark population declines can be challenging to determine due to the sporadic nature of shark attacks and the complexity of marine ecosystems. Additionally, public perception and media interest in shark attacks can influence the interpretation of data and the development of conservation policies.
