Why do shark bites seem to be more deadly in Australia than elsewhere?



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White sharks’ ability to stay warm in cold water makes them efficient long-range hunters.
Denice Askebrink

Blake Chapman, The University of Queensland

The first thing to say about shark attack deaths is that they are very rare, with only about two per year in Australia. But still, every year without fail, people die from shark bites, both here and around the world.

According to official statistics, the United States records by far the most unprovoked shark bites – an average of 45 per year over the past decade. However, only 1.3% of these incidents were fatal – 0.6 deaths per year.

Australia records fewer bites than the US (an average of 14 per year), but a much greater proportion of them are deadly: (1.5 per year, or close to 11%). So what is it that (relatively speaking) makes Australia more prone to deadly shark attacks?


Read more: Not just nets: how to stop shark attacks without killing sharks


My new book Shark Attacks: Myths, Misunderstandings and Human Fear addresses this and other questions about sharks, with the aim of dispelling common myths and providing the knowledge needed for decisions made on science rather than fear and emotion.

A perfect storm

In a way, Australia has a “perfect storm” of conditions for serious shark attacks. The first reason is that Australians (and visitors to Australia) love the ocean. Some 85% of Australians live within 50km of the coast, and Australian coastal areas account for the most prominent growth outside of capital cities. Beaches are also favoured recreational destinations in Australia and coastal locations are heavily targeted in tourism, attracting nearly 60% of international tourists.

Next, the sharks themselves. Australia has the world’s highest diversity of sharks and rays, including roughly 180 of the 509 known shark species.

But neither of these factors, even taken together, is enough to explain why deaths are more prevalent in Australia. What we really need to look at is dangerous sharks.

Only 26 shark species have been definitively identified as biting humans without provocation, although the true number is likely to be somewhat higher. Of these 26 species, 22 (85%) are found in Australian waters.

All 11 of the species known to have caused fatal unprovoked bites on humans can be found in Australian waters. And crucially, Australia’s coastal waters are home to all of the “big three” deadly species: white sharks, tiger sharks, and bull sharks.

Australia’s waters are home to all three of the ‘big three’ shark species.
Denice Askebrink

These species account for all but three of the 27 fatal shark attacks worldwide from 1982-2011. All of the big three species are inquisitive, regularly frequent coastal environments, and are formidably big and strong.

They also have complex, unpredictable behaviour. But despite this difficulty, we can identify factors that make them more likely to swim in areas routinely used by humans.

Warming to it

White sharks have a physiological adaptation that allows them to maintain a vast global distribution, and hence are responsible for the northernmost and southernmost recorded shark bites on humans.

Most fish are ectothermic, or cold-blooded, with body temperatures very close to that of the surrounding water. This restricts their range to places where the water temperature is optimal.

In contrast, white sharks and a few other related species can retain the heat generated by their muscles predominantly during swimming, enabling them to be swift and agile predators even in cold water. They do this with the help of bunches of parallel arteries and veins in their brains, eyes, muscles and stomachs that function as “heat exchangers” between incoming and outgoing blood, allowing them to keep these crucial organs warm.

White sharks are so good at retaining heat that their core body temperature can be up to 14.3℃ above the surrounding water temperature. This allows them to move seasonally up and down Australia’s east and west coasts, presumably following migrating prey species.

Getting salty

Bull sharks, meanwhile, are the only sharks known to withstand wide variations in water salinity. This means they can easily move from salty oceans to brackish estuaries and even travel thousands of kilometres up river systems. As a result they can overlap with human use areas such as canals, estuaries, rivers and even some lakes. One female bull shark was observed making a 4,000km round-trip to give birth in a secluded Madagascan estuary rather than the open ocean.

As a result, most bull sharks found in river systems are juveniles, but these areas may also be home to large, pregnant females who need to eat more prey to sustain themselves. As rivers are often clouded by sediment, there is an increased risk that a human may be mistaken for prey in this low-visibility environment.

Bull sharks can roam in rivers as well as oceans.
Albert Kok/Wikimedia Commons

Opportunistic tigers

Tiger sharks mainly stay in coastal waters, although they also venture into the open ocean. Their movements are unpredictable, they eat a wide range of prey, are naturally curious and opportunistic, and can be aggressive to humans.

Tiger sharks are clever too – they are thought to use “cognitive maps” to navigate between distant foraging areas, and have hunting ranges that span hundreds of thousands of square kilometres so as to maintain the element of surprise. As a result, tiger sharks’ distribution in Australian waters covers all but the country’s southern coast.

Tiger sharks like to keep their prey guessing.
Albert Kok/Wikimedia Commons, CC BY-SA

Read more: Finally, a proven way to keep great white sharks at arm’s length


Taken together, it’s clear that Australia’s waters are home to three predators that can pose a real danger, even if only an accidental one, to humans.

But remember that shark attacks are incredibly rare events, and fatal ones even rarer still. There are also lots of tips we can use to minimise the risk of having a negative encounter with a shark.

The ConversationDon’t swim in murky, turbid or dimly lit water, as sharks may not be able to see you properly (and you may not be able to see them). Avoid swimming in canals, or far from the shore, or along dropoffs. Swim in designated areas and with others, and avoid swimming where baitfish (or bait) may be present. And of course, always trust your instincts.

Blake Chapman, Adjunct Research Fellow, Science Communicator, The University of Queensland

This article was originally published on The Conversation. Read the original article.

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Can buying up fishing licences save Australia’s sharks?


Christopher Brown, Griffith University and Samantha Munroe, Griffith University

The World Wildlife Fund (WWF) recently raised over A$200,000 to buy shark fishing licences in Queensland’s waters. They estimate the licences, for operating nets in and around the Great Barrier Reef Marine Park, could have been used to catch 10,000 sharks each year.

Retiring these licences is a new development in Australian shark conservation, but may also limit locally caught seafood.

But do Australia’s sharks need saving, or can we eat them? It depends on where you look.

Sustainable sharks

Sharks in general are much more vulnerable to overfishing than other fish. Compared to most fish, sharks have far fewer offspring over their lifetimes. As a result, shark populations cannot tolerate the same levels of fishing that fish can sustain.

Globally, there is great reason for concern over the status of sharks. About a quarter of all sharks and rays are threatened with extinction. The high value of shark fins in Asian markets drives a large and often unsustainable shark fishery that reaches across the globe.

Australia has an important role to play in combating this trend. Many species that are globally threatened can find refuge in the Great Barrier Reef Marine Park, which has an extensive system of protected areas and comparatively low fishing effort. Despite this potential safe haven, some species in Australia still rest on an ecological knife edge.

A white-tip reef shark in the Great Barrier Reef Marine Park.
Christopher Brown

For example, the great and scalloped hammerheads (which the WWF says will benefit from the licence purchase) are both by-catch species in the Australian fishery and are listed by the International Union for Conservation of Nature as endangered.

Australian fishermen don’t head out to catch hammerheads intentionally; most people do not consider the meat palatable. However, their hammer-shaped head is easily entangled in nets. Therefore hammerheads may be highly susceptible to any increase in fishing pressure.

Commercial fishers are legally required to have a licence. By buying the licences, WWF can limit the number of active nets in the water.

However, not all shark species are as vulnerable to fishing as the iconic hammerhead. Several shark species in Australia are well-managed. For instance, the spot tail shark is fast-growing and has many young, making it relatively resilient to fishing pressure. Many Australians regularly enjoy these species with a side of chips.

Species targeted by Queensland’s shark fishery are likely sustainable. The latest fishery assessment published by the Queensland government in 2014 found that catches of most shark species were well within safe limits.

Supporting our local shark fisheries is therefore far better than importing shark from overseas where fisheries may be poorly managed.

But it is not all good news in Australia. Both the assessment and an independent review found that while Queensland’s shark catch likely is sustainable, we need to be cautious about allowing any increases.

Importantly, Queensland’s 2014 shark assessment relies on very limited data. A crucial fishery observer program was cut in 2012. The limited data mean that regulations for Queensland’s shark catches are set conservatively low. Any increase in catch is risky without an assessment based on higher-quality data.

Scientists use tag-and-release programs to track the movements and population size of sharks. But more direct fisheries data are needed.
Samantha Munroe

A win for fishers and fish

Buying up licences in an uncertain fishery may be an effective way to prevent the decline of vulnerable species. Although buying licences is a new move for marine conservation groups in Australia, elsewhere it has proven an effective strategy for conservation and fisheries.

For instance, in California the conservation group Nature Conservancy bought fishing licences for rockfish, some species of which are endangered.

The Nature Conservancy now leases those licences back to fishers that promote sustainable fishing methods. The fishers themselves can charge a higher price for sustainable local catches of fish. What started as a move purely for conservation has had benefits for those employed in fisheries.

The lesson here is that conservation organisations can be the most productive when they work with, not against, fisheries. The recent shark licence purchase in Australia could be a great opportunity for fishers and conservation organisations to work together to maintain healthy ecosystems and fisheries.

But if Australians are serious about protecting sharks, there are other steps we still need to take. Queensland should reinstate the fishery observer program so we have reliable data to assess shark populations. For instance, currently we don’t know how many sharks are caught as by-catch in other fisheries.

A lemon shark seeks its fish prey in the shallow waters on Australia’s Great Barrier Reef. Lemon sharks are caught by our fisheries, but are not a target species.
Megan Saunders

Shark control programs designed to protect bathers are also a threat to endangered shark populations. However, data on deaths from shark control in Queensland were not accounted for in the government’s catch limits.

Accounting for these missing deaths could make a serious dent in our sustainable catch, an independent review found.

There is an opportunity to address these issues in Queensland’s upcoming fisheries management reform. Have your say here.

If conservation groups can work with fisheries, a more consistent and sustainable shark-fishing strategy may emerge. Australians can continue to be proud of our efforts to protect marine life, but can still enjoy shark for dinner.

The Conversation

Christopher Brown, Research Fellow, Australian Rivers Institute, Griffith University and Samantha Munroe, Postdoctoral research fellow, Australian Rivers Institute, Griffith University

This article was originally published on The Conversation. Read the original article.

Helping protect endangered sharks


Parks Australia

Southern Cross University has completed a limited study on behalf of Parks Australia in the Cod Grounds Commonwealth Marine Reserve to give us a better idea of how the reserve and management actions are contributing to protecting this important aggregation site for the east coast population of the critically endangered grey nurse shark. The reserve was first proclaimed in 2007 and is located in Commonwealth waters just south of Port Macquarie, NSW.

The study found preliminary evidence that the conservation benefits of the reserve included enhanced diversity, target fish abundances and grey nurse shark prey densities compared to areas open to fishing outside the reserve. On average 29 per cent greater species richness was found in the reserve compared to the surrounding reef area open to fishing with wrasses, breams, drummers and sharks and rays contributing strongly to this pattern. Four individual grey nurse sharks were observed in the reserve…

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