Forget sharks… here’s why you are more likely to be injured by litter at the beach



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Sadly, people plus beach equals litter, so be careful out there.
Wikimedia Commons

Marnie Campbell, Murdoch University; Cameron McMains, Murdoch University; Chad Hewitt, Murdoch University, and Mariana Campos, Murdoch University

Our beaches are our summer playgrounds, yet beach litter and marine debris injures one-fifth of beach users, particularly children and older people.

Our research, published in the journal Science of the Total Environment, found more than 7,800 injuries on New Zealand beaches each year – in 2016, some 595 of them were related to beach litter. The most common injuries caused by litter were punctures and cuts, but they also included fractured limbs, burns, head trauma, and even blindness.

Children under 14 suffered 31% of all beach litter injuries, and were injured by beach litter at twice the rate compared with other locations in New Zealand. Beach litter injury claims exceeded NZ$325,000 in 2016, representing a growing proportion of all beach injury claims. Beach injury claims changed from 1.2% of the total in 2007 to 2.9% in 2016.




Read more:
This South Pacific island of rubbish shows why we need to quit our plastic habit


Our study relied on reported injury insurance claims in New Zealand, and thus probably underestimates the true injury rate, particularly for minor wounds. Our 2016 survey of beachgoers in Tasmania found that 21.6% of them had been injured by beach litter at any time previously – even on the island state’s most picturesque beaches.

Alarmingly, most beach users in the Tasmanian survey did not consider beach litter an injury risk, despite the high rate of self-reported injuries.

Awash with danger

As more debris washes ashore and our recreational use of our coasts increases, it is more likely than ever before that we will encounter beach litter, even on remote and “pristine” beaches.

Global studies have found up to 15 items of debris per square metre of beach, even in remote locations. On Henderson Island – a supposedly pristine South Pacific outpost miles from anywhere – some 3,570 new pieces of litter arrive every day on one beach alone.

Beach litter typically includes a huge range of items, such as:

  • broken glass
  • sharp and rusted metal such as car bodies, food cans, fish hooks, and barbed wire
  • flammable or toxic materials such as cigarette lighters, flares, ammunition and explosives, and vessels containing chemicals or rotten food
  • sanitary and medical waste such as used syringes, dirty nappies, condoms, tampons and sanitary pads
  • bagged and unbagged dog faeces and dead domestic animals.

The health hazards posed by beach litter include choking or ingesting poisons (particularly for young children), exposure to toxic chemicals, tripping, punctures and cuts, burns, explosions, and exposure to disease.

Degrading plastic can also produce toxins that contaminate seafood, potentially entering human or ecological food chains.

Rubbish knowledge

Despite the potential severity of these hazards our understanding and study of human health impacts from beach litter is poor. We know more about the impacts of beach litter and marine debris on wildlife than on humans.

Two of our previous studies in Australia and New Zealand have found beach litter that can cause punctures and cuts at densities 227 items per 100 square metres of beach, and choking hazards at densities of 153 items per 100 square metres of beach. These exposures to beach litter hazards in Australia and New Zealand may be 50% higher than global averages (based on preliminary data).




Read more:
How much plastic does it take to kill a turtle? Typically just 14 pieces


Even “clean” beaches can be hazardous, and may even increase the likelihood of injury. Visitors to a recently cleaned or supposedly “pristine” beach may be less vigilant for hazards. What’s more, European studies have found that actively cleaned beaches can still have hazardous debris items.

The risk of injury will continue to increase without concerted efforts to prevent addition of new debris and the active removal of existing rubbish. Besides watching where we tread when at the beach and participating in beach cleanups, we also need to make sure we deal with rubbish thoughtfully, so litter doesn’t end up there in the first place.The Conversation

Marnie Campbell, Chevron Harry Butler Chair in Biosecurity and Environmental Science, Murdoch University; Cameron McMains, PhD Candidate, Harry Butler Institute, Murdoch University; Chad Hewitt, Professor and Director, Murdoch Biosecurity Research Centre, Murdoch University, and Mariana Campos, Lecturer and researcher, Murdoch University

This article is republished from The Conversation under a Creative Commons license. Read the original article.

Some sharks have declined by 92% in the past half-century off Queensland’s coast



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Scalloped hammerhead entangled in a Queensland shark control net at Magnetic Island, Townsville.
Courtesy of Nicole McLachlan

George Roff, The University of Queensland and Christopher Brown, Griffith University

There has been a striking decline in the number of large sharks caught off Queensland’s coast over the past 50 years, suggesting that populations have declined dramatically.

Our study, published today in the journal Communications Biology, used historical data from the Queensland Shark Control Program.

Catch numbers of large apex sharks (hammerheads, tigers and white sharks) declined by 74-92%, and the chance of catching no sharks at any given beach per year has increased by as much as seven-fold.

Coinciding with ongoing declines in numbers of sharks in nets and drum lines, the probability of recording mature male and females has declined over the past two decades.

Tiger sharks have undergone a 74% decline in numbers over the past half century.
Juan Oliphant/www.oneoceandiving.com

Our discovery is at odds with recent media reports of “booming” shark numbers reaching “plague” along our coastlines. The problem with those claims is that we previously had little idea of what the “natural” historical shark population would have been.

Why is the decline of sharks on the Queensland coastline a cause for concern? Large apex sharks have unique roles in coastal ecosystems, preying on weak and injured turtles, dolphins and dugongs, actively scavenging on dead whale carcasses, and connecting coral reefs, seagrass beds and coastal ecosystems.

Australia’s mixed view on sharks

As a nation, Australia has a long history with sharks. Some of the oldest stories in the world were written by the indigenous Yanyuwa people in the Northern Territory some 40,000 years ago, describing how the landscape of their coastal homeland was created by tiger sharks.

European settlers in the late 18th and early 19th centuries further described Australian coastlines as being “chock-full of sharks”, and upon visiting Sydney in 1895, the US author Mark Twain remarked:

The government pays a bounty of the shark; to get the bounty the fishermen bait the hook or the seine with agreeable mutton; the news spreads and the sharks come from all over the Pacific Ocean to get the free board. In time the shark culture will be one of the most successful things in the colony.

With the rise of Australian beach and surf culture, and the growing population density in coastal communities in the mid-20th century, increasing numbers of unprovoked fatal encounters with sharks occurred along the Queensland and New South Wales coastlines.

White sharks were extensively targeted and killed in “game fishing” tournaments, and harmless grey nurse sharks were hunted almost to extinction through recreational spearfishing in the 1950s and 1960s.

Yet despite this long history of shark exploitation, the historical baseline populations of sharks off Australia’s east coast were largely unknown.

Historical photograph of contractors measuring sharks removed from QSCP nets on the Gold Coast in the early years of the program (3rd November 1963).

Through mesh nets and baited drumlines, the Queensland Shark Control Program targets large sharks, with the aim of reducing local populations and minimise encounters between sharks and humans. Records of shark catches dating back as far as the 1960s provide a unique window into the past on Queensland beaches.

While we will never know exactly how many sharks roamed these waters more than half a century ago, the data points to radical changes in our coastal ecosystems since the 1960s.

The exact causes of declining shark numbers are difficult to pinpoint, largely because of a lack of detailed records from commercial or recreational fisheries before the 2000s. The Queensland government also acknowledges that the program itself has a direct impact on shark populations by selectively removing large, reproductively mature sharks from the population.

The data indicates that two hammerhead species – the scalloped and great hammerheads, both of which are listed as globally endangered – have declined by as much as 92% in Queensland over the past half century.

Similarly, the once-abundant white sharks have also shown no sign of recovery, despite a complete ban on commercial and recreational fishing in Queensland, implemented more than two decades ago.

The idea that shark populations are reaching “plague” proportions in recent years may represent a classic case of shifting baseline syndrome. Using shark numbers from recent history as a baseline may give a false perception that populations are “exploding”, whereas records from fifty years ago indicate that present day numbers are a fraction of what they once were.

Our results indicate that large shark species are becoming increasingly rare along Australia’s coastline. We should not be concerned about a “plague” of sharks, but rather the opposite: the fact that previously abundant apex shark species are increasingly at risk.The Conversation

George Roff, Postdoctoral Research Fellow, The University of Queensland and Christopher Brown, Research Fellow, Australian Rivers Institute, Griffith University

This article is republished from The Conversation under a Creative Commons license. Read the original article.

Shark tourism can change your mind about these much-maligned predators



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Getting up close and personal can make you like sharks more, even if you already like them.
Juan Oliphant, Author provided

Michele Barnes, James Cook University and Sarah Ruth Sutcliffe, James Cook University

Shark ecotourism can change people’s attitudes about sharks and make them more likely to support conservation projects – even after allowing for the fact that ecotourists are more likely to be environmentally minded in the first place.

In our research, published in the journal Marine Policy, we surveyed 547 participants in a shark ecotourism program oriented towards education and conservation off the coast of Oahu, Hawaii.

We looked at participants’ knowledge of and attitudes towards sharks, and their intention to engage with shark conservation projects before and after the tour. We then compared these with the knowledge, attitudes, and conservation intentions of 488 members of the public who had not taken part in shark ecotourism.




Read more:
Friday essay: The Meg is a horror story but our treatment of sharks is scarier


Even before taking part in the shark ecotourism program, participants were generally more environmentally minded, more knowledgeable about sharks, and had more positive attitudes towards sharks than the general public.

For example, 71% of participants had positive attitudes towards sharks before the tour, compared with only 45% of the general public. To a certain extent, therefore, the shark ecotourism program was attracting people who were already “converted” to environmentalism.

But, crucially, we also found that after the ecotourism program, participants had significantly more knowledge of the ecological role of sharks and a more favourable attitude towards them. There was a 39% increase in knowledge along our measured scale, and 97% of participants who held negative attitudes ended up changing their mind about sharks as a result of the tour.

Ultimately, the program had a significantly positive effect on people’s intentions to engage in shark conservation behaviour, despite them already being more environmentally minded than the general public. In other words, these programs are not just “preaching to the converted” – they really do improve people’s engagement with conservation.

Learning to love sharks?
Juan Oliphant, Author provided

Sharks’ PR problem

Sharks are crucial to our marine ecosystems, yet many shark populations are in decline as a result of fishing (particularly for shark fin soup), fisheries bycatch, habitat destruction, and climate change.

To survive, sharks need a coordinated global conservation effort. And for that they need people to speak up for them.

Unfortunately, sharks have a PR problem. They are feared by many members of the public, demonised by the media, treated as human-hunting monsters, and cast as the villains in blockbuster movies like Jaws and The Meg. In many places, government-funded programs actively cull sharks in the name of beachgoers’ safety.




Read more:
Feeding frenzy: public accuse the media of deliberately fuelling shark fear


Winning hearts and minds

Shark ecotourism provides an opportunity to learn about sharks’ role in ocean ecosystems, and to view and interact with them in their natural environment. Our research suggests it offers a way to counteract misconceptions and build support for shark conservation.

Not all programs marketed as shark ecotourism are equal, however. There are legitimate concerns about some forms of shark tourism, with important questions about animal welfare, ecological impacts, and public safety (particularly where chum or bait is used to attract sharks).

The conservation benefits of shark ecotourism are thus most likely to be realised when it is conducted responsibly, with trained staff, in areas that don’t conflict with other ocean uses.

Hopefully, our findings will encourage the development of responsible, environmentally friendly and educational shark ecotourism programs with specific conservation goals, which will allow people to engage with sharks in a positive way. In turn, that could help to build political and social pressure to conserve sharks.The Conversation

Michele Barnes, Environmental Social Science Research Fellow, James Cook University and Sarah Ruth Sutcliffe, Marine Social Sciences PhD candidate, James Cook University

This article is republished from The Conversation under a Creative Commons license. Read the original article.

FactFile: the facts on shark bites and shark numbers



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The CSIRO has provided new estimates of population sizes for White Sharks in Australian waters.
Fiona Ayerst/Shutterstock

Jane Williamson, Macquarie University and Vincent Raoult, University of Newcastle

Are there more sharks in Australian waters than there used to be, and are interactions between humans and shark increasing? Some Australian politicians have claimed that to be the case.

Let’s look at the research.

The most reputable source for shark incident data in Australia is the Australian Shark Attack file, which is collated at Sydney’s Taronga Zoo.

The map below, created by The Conversation using data from the Australian Shark Attack File, shows incidents between sharks and humans in Australia between 1997 and 2017.

You can use the filter buttons in the map to explore the data by year, season, the type of injury, the type of shark involved, the type of incident – or a combination of all the filters. Press the ‘show all’ button to reset the search.

https://cdn.theconversation.com/infographics/243/f87e27e72eb6545d5422e204b9894dedaad0f92f/site/index.html

The number of recorded encounters between sharks and humans in Australia increased modestly between 1997 and 2017, but the reason for this is unclear. Over those two decades, the Australian population increased by 33%, but that alone doesn’t explain the increase in recorded shark encounters.

Correcting for the growth in human population in Australia, the data show that between 1997 and 2017:

  • incidents resulting in injury increased by 1.59%
  • incidents without injury increased by 0.36%, and
  • fatalities increased by 0.07%.

Encounters between humans and sharks are extremely variable over time, and difficult to predict. The increases in recorded incidents between 1997 and 2017 are relatively small, and may be explained by factors not related to shark populations – such as increases in the reporting of shark encounters, or increasing beach use.

https://cdn.theconversation.com/infographics/159/62c30e6dedecffbbeb4e059c8ab0e573d756f61b/site/index.html

Are there more sharks off the Australian coast?

White Sharks (formerly Great White Sharks) are recorded as being responsible for 28 of the 36 fatal shark encounters in Australian waters between 1997 and 2017, and are the primary target of shark mitigation strategies of the Western Australian, New South Wales and Queensland governments.

So, has there been an increase in the number of White Sharks in Australian waters?

Estimating population numbers in the marine environment is difficult, especially for long-lived migratory species like White Sharks.

However, there is no evidence that White Sharks numbers are on the rise, either in Western Australia or along the Eastern coast. Despite targeted conservation efforts, the available research show stable or slightly declining numbers in these populations.

There are two distinct populations of White Sharks off Australian coasts – one to the west, and another to the east of Bass Strait, which separates Tasmania from mainland Australia. The eastern population includes New Zealand White Sharks.

Recent work by the CSIRO through the National Environmental Science Program’s Marine Biodiversity Hub using innovative DNA analysis has provided us with the most detailed and reliable estimates of population size we have for this species.

The CSIRO study shows there has been a slight decline in adult White Shark populations since the year 2000.

Current adult abundance for the eastern Australasian population is estimated at 750, with an uncertainty range of 470 to 1,030. The southern-western adult population is roughly double the size, estimated at 1,460, with an uncertainty range of 760 to 2,250.

Including the available information about juvenile White Sharks, estimates of total size for the eastern population in 2017 was 5,460, with an uncertainty range of 2,909 to 12,802.

It’s difficult to detect population trends with White Sharks because of the length of time it takes juveniles to reach maturity – around 15 years. As protection of White Sharks began in the late 1990s, any changes in abundance would only be starting to appear in current populations.

How else can we measure White Shark populations?

The traditional way of measuring shark and fish populations is by examining catches in commercial fisheries over long time periods. By correcting for the level of fishing effort – which is done by looking at things like the number of nets, hooks and tows deployed by fishermen – scientists can assume that changes in the “catchability” of sharks is related to their abundance.

But due to the relative rarity of catches of White Sharks by fishing vessels, this approach is less reliable for this species than the more recent genetic studies conducted by the CSIRO and outlined above.

Western Australia has a detailed measure of White Shark numbers assessed by catch data. A report published by the Western Australian Department of Fisheries in 2016 attempted to model changes in the southern-western Australian White Shark population since the late 1930s. The authors outlined four different plausible scenarios, none of which suggested a continuous increase in the number of White Sharks.

In New South Wales, there has been a cluster of shark bites in recent years. Data from the NSW Shark Meshing (Bather Protection) Program, managed by the NSW Department of Primary Industries, show a recent increase in White Sharks caught in nets placed near ocean beaches.

But when it comes to thinking about shark populations, we should not assume that these two facts are related. It’s important to remember that just because two things may correlate, it doesn’t mean that one caused the other.

These patterns could mean that the animals are coming closer to shore, rather than a population increase (or decrease).


https://datawrapper.dwcdn.net/Zzcem/2/


Shark and human interactions: what factors are at play?

A 2016 paper examined six global shark bite “hotspots” – the United States, South Africa, Australia, Brazil, Reunion Island and the Bahamas – and concluded that when it comes to encounters between sharks and humans, there are a range of causes at play.

These include:

  • rises in human population
  • habitat destruction/modification
  • changes in water quality
  • climate change
  • changing weather patterns, and
  • the distribution/abundance of prey.

The authors also noted that shark encounters appear to happen in clusters. For example, 2009 saw a spike in shark encounters off the New South Wales coast. This coincided with an increase in beach attendance and beach rescues during what was an unusually warm summer for south-east Australia.

A 2011 paper highlighted the popularity of water sports as a factor contributing to increased human-shark encounters. More people are taking part in water sports, and improvements in wetsuit technology mean that people are in the water for longer throughout the year.

However, there is limited information on the number of people who use Australian beaches, so this explanation needs to be further studied.

The ConversationIt’s vital that any strategies put in place to reduce the number of unprovoked encounters between humans and sharks in Australian waters are carefully considered, and based on the best available research.

Jane Williamson, Associate Professor in Marine Ecology, Macquarie University and Vincent Raoult, Postdoctoral fellow, University of Newcastle

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

Tide turned: surveys show the public has lost its appetite for shark culls


Christopher Neff, University of Sydney and Thomas Wynter, University of Sydney

A Senate Committee report on shark deterrent measures has, in the words of committee member Senator Peter Whish-Wilson, moved the “shark cull debate into the 21st century”.

The first recommendation of the inquiry is to “immediately replace lethal drum lines” with so-called SMART drum lines and to phase out shark nets.

Yet if the news media are to be believed, these conclusions go against the grain of public opinion, with Western Australia’s spate of shark incidents having spawned previous headlines such as “Calls grow louder for shark culling in WA”. More recently, a series of incidents in Ballina in northern New South Wales prompted our surfing former prime minister Tony Abbott to weigh in, calling on the state government to authorise culls and nets.


Read more: Sharks aren’t criminals, but our fear makes us talk as if they are


The question of how much the public really supports policies that kill sharks has been surprisingly difficult to answer. The Senate inquiry noted that while it had been suggested “that lethal measures such as nets are no longer supported … reliably ascertaining community views on matters such as this could be quite difficult”.

Difficult? Yes. But doable. We have surveyed public opinion in Western Australia and Ballina, following shark bite incidents in each place. In fact, over the past five years we have searched high and low for the type of widespread support for lethal policies that is suggested by the tabloid press. It simply is not there, as our findings in the peer-reviewed journals Conservation Letters and Marine Policy show.

Public opinion in Perth and Ballina

In fieldwork including phone polling in both Perth and Ballina, as well as face-to-face surveys of local residents, beachgoers, and business owners in Ballina, we consistently found levels of support for lethal policies in the 20-25% range.

This is particularly remarkable in the case of Ballina. As the shire’s mayor David Wright told the Senate committee, between 8 February 2015 and July 2016, surfers there “were involved in 9% of the world’s shark attacks and interactions”, with the media dubbing it the “shark attack capital of Australia”.

A large majority of people in both Perth and Ballina viewed shark bites as accidental rather than intentional. While fear of sharks is linked to higher support for lethal policies, fear alone does not cause people to support killing sharks.

Support for lethal policies arises when fear of sharks is combined with the misconceived idea that sharks bite people on purpose. In our surveys, respondents who view shark bites to be intentional were more than 2.5 times as likely to support policies that kill sharks.


Author provided

This is strongly related to the Senate inquiry’s finding that the belief that “killing ‘rogue’ sharks will solve the problem” remains widespread. This is despite a clear expert consensus that there is “no evidence for anything called a rogue shark”.

As the Department of the Environment and Energy says, “No shark is thought to target humans as prey”, and the vast majority of shark bite incidents “can be attributed to the shark confusing us with its normal prey”.

This view was apparent among the relatively few beachgoers in Ballina who reported supporting lethal policies, with several respondents suggesting that they would only support killing sharks that “had gotten a taste for human flesh”.

Many respondents were also unaware that shark nets are lethal to sharks. Indeed, this is their primary purpose, as the Senate inquiry noted: “It is not intended that the nets create an enclosed area: rather, they are a passive fishing device designed to cull sharks in the area.”

Understanding overcomes fear

Our second study looked specifically at the interaction between fear of sharks and the perception that they bite humans intentionally.

We carried out an experiment in the Sydney SEA LIFE Aquarium’s “shark tunnel” – a one-way, U-shaped exhibit that provides perfect conditions for our study. We divided participants into two groups and assigned one group to a treatment to “prime” their emotions at the beginning of the exhibit.

We also surveyed all participants about their feelings about and perceptions of sharks, after viewing the exhibit. This also allowed us to capture both a before and after measurement of fear, from which we could determine whether people’s fear had subsided after seeing sharks’ behaviour at first hand.

We tested two “priming” messages. One called attention to the low probability of being bitten by a shark – we call this our Probability Prime. A second priming message drew “attention to intentionality”. This was our Intentionality Prime and it prompted aquarium visitors to consider sharks’ behaviours.

The Probability Prime, which reflects standard marine education attempts to reduce fear of sharks, failed to do so, consistent with research showing humans overestimate low probability risks. Crucially, considering our findings in Ballina and Perth, the Intentionality Prime successfully reduced the public’s fear of sharks.

shark fear.
Author provided

There are five take-home messages from our research results:

  1. There is little blame on the shark. The tide has turned and the public is sophisticated enough to understand that sharks are not intentionally hurting people.

  2. There is little blame on the government. Governments that feel they need to continue using shark nets or else face the wrath of the public following a shark bite should rework their political calculations.

  3. The public no longer supports policies that kill sharks. In WA, 75% supported non-lethal options, in Ballina the number was 83% and in the Sydney experiment it reached 85%.

  4. A Save the Sharks movement has begun, with the public we have polled consistently voicing greater support for conservation approaches above killing sharks.

  5. Survey respondents believe that governments choose lethal measures to ease public concern, not to make beaches safer. This is a problem for Australia’s democracy; the public believes that policies are being designed to protect governments, not people.

The ConversationThis last point is arguably the most serious flaw of all in these policies: the continued killing of sharks for political gain.

Christopher Neff, Lecturer in Public Policy, University of Sydney and Thomas Wynter, Postdoctoral Research Associate, Electoral Integrity Project, University of Sydney

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

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.