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

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.

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.

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The small patch of bush over your back fence might be key to a species’ survival

A kangaroo finds refuge in a small patch of vegetation surrounded by a new housing estate.
Georgia Garrard, Author provided

Brendan Wintle, University of Melbourne and Sarah Bekessy, RMIT University

It may not look like a pristine expanse of Amazon rainforest or an African savannah, but the patch of bush at the end of the street could be one of the only places on the planet that harbour a particular species of endangered animal or plant.

Our newly published global study of the conservation value of landscapes in 27 countries across four continents has found these small patches of habitat are critical to the long-term survival of many rare and endangered species.

In Australia, our cities are home to, on average, three times as many threatened species per unit area as rural environments. This means urbanisation is one of the most destructive processes for biodiversity.

It tends to be the smaller patches of vegetation that go first, making way for a housing development, a freeway extension, or power lines. Despite government commitments to enhance the vegetation cover of urban areas and halt species extinctions, the loss of vegetation in Australian cities continues.

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This story plays out all over the world day after day. Of course, it’s not just an urban story. Patches of rural vegetation are continually making way for, say, a new pivot irrigation system or a new mine to provide local jobs.

Remnant salmon gum woodland surrounded by cropland near Bencubbin in Western Australia’s northeast wheatbelt.
Mike Griffiths, Author provided

Mostly, policymakers and scientists do not consider these losses to be, on their own, a fatal blow to the biodiversity of a region or country. Small, often isolated patches of vegetation are considered expendable, tradeable, of limited ecological value due to their small size and relatively large amount of “edgy” habitat. Wrong.

Research forces a rethink

Our study analysed the relationship between conservation value of vegetation patches and their size and isolation in landscapes across Europe, Australia, North America and Africa. The findings prompt a rethink of long-held views about the relative importance of small, isolated habitat patches for biodiversity conservation. We show that these patches often have unique ecological and environmental characteristics.

The critically endangered Western Ringtail Possum lives mainly in small habitat patches in or around urban areas near Perth and is under intense pressure from housing development, foxes, cats and dogs.
Yokochi K., Bencini R./Wikimedia Commons, CC BY

That’s because they are the last patches left over from extensive clearing of flat, fertile land for agriculture or urban growth close to rivers and bays. They often contain habitats for rare or endangered species that have disappeared from the rest of the landscape. This makes these small, isolated patches of habitat disproportionately important for the survival of many species.

Our study calls for a rethink of urban planning and vegetation management regulations and policies that allow small patches of vegetation to be destroyed with lower (and often zero) scrutiny. We argue that the environment is suffering a death by a thousand cuts. The existence of large conservation reserves doesn’t compensate for the small patches of habitat being destroyed or degraded because those reserves tend to contain different species to the ones being lost.

The combined impact of the loss of many small patches is massive. It’s a significant contributor to our current extinction crisis.

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Let’s get this straight, habitat loss is the number-one threat to Australia’s species

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Why are small patches seen as dispensable?

A key variable used in decisions on vegetation-clearing applications is the size of patch being destroyed. Authorities that regulate vegetation management and approve applications are more permissive of destruction of small patches of vegetation.

This is partly due to a large body of ecological theory known as island biogeography theory and subordinate theories from metapopulation ecology and landscape ecology. These theories suggest that species richness and individual species’ population sizes depend on the degree of isolation of the patch, its size and the quality of the habitat it contains.

While it is crucial that we conserve large, intact landscapes and wilderness, the problem with conserving only large and well-connected patches of high-quality vegetation is that not all species will be conserved. This is because some species exist only in small, isolated and partially degraded habitats, such as those characteristic of urban bushlands or remnant bush in agricultural areas.

A remnant wetland is still valuable habitat for species like the Pacific Heron.
Wayne Butterworth/Wikimedia Commons, CC BY

For this reason, we highlight the importance of protecting and restoring habitats in these small isolated patches. And these areas do tend to be more vulnerable to invasion by weeds or feral animals. If the impacts of invasive species are not managed, they will eventually lead to the destruction of the habitat values and the loss of the species those habitats support.

Small and isolated patches of vegetation on the urban fringe are under enormous pressure from human use, pets, escaped seed of Agapanthus and the many other invasive species we plant in our gardens. These plants spread into local bushland, where they outcompete the native plants.

Communities can make a difference

As well as these perils, being on the urban fringe also brings opportunity. If a remnant patch of vegetation at the end of the street is seen to be of national environmental importance, that presents a great opportunity to channel the energies of community groups into conserving and restoring these patches.

A patch that is actively cared for by the community will provide better habitat for species. It’s also less likely to fall foul of development aspirations or infrastructure projects. The vicious cycle of degradation and neglect of small patches of habitat can be converted into a virtuous cycle when their value is communicated and local communities get behind preserving and managing them.

Volunteer community groups can play a vital role in preserving and enhancing small habitat patches.
Robin Clarey, Friends of Edithvale Seaford Wetlands, Author provided

Urban planners and developers can get on board too. Rather than policies that enable the loss of vegetation in urban areas, we should be looking at restoring habitats in places that have lost or are losing them. This is key to designing healthy, liveable cities as well as protecting threatened species.

Biodiversity-sensitive urban design makes more of local vegetation by complementing the natural remnant patches with similar habitat features in the built environment, while delivering health and well-being benefits to residents. Urban development should be seen as an opportunity to enhance biodiversity through restoration, instead of an inevitable driver of species loss.

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Here’s how to design cities where people and nature can both flourish

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Brendan Wintle, Professor Conservation Ecology, University of Melbourne and Sarah Bekessy, Professor, RMIT University

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

We can’t know the future cost of climate change. Let’s focus on the cost of avoiding it instead

Economists have searched for the mythical balance between the cost of climate action, and the future cost of doing nothing.
Joop Hoek/Shutterstock.com

Jack Pezzey, Australian National University

As delegates at the UN climate summit in Katowice, Poland, discuss the possibility of restraining global warming to 1.5℃, it might sound like a reasonable question to ask how much money it will cost if they fail.

Economists have spent the past 25 years trying – and largely failing – to agree on the “right” answer to this question. It’s an important consideration, because governments are understandably keen to balance the benefits of limiting long-term climate damage with the more immediate costs of reducing greenhouse emissions.

In simple economics terms, we can ask what price would be worth paying today to avoid emitting a tonne of carbon dioxide, given the future damage costs that would avoid.

This mythical figure has been called the “social cost of carbon”, and it could serve as a valuable guide rail for policies such as carbon taxes or fuel efficiency standards. But my recent research suggests this figure is simply too complicated to calculate with confidence, and we should stop waiting for an answer and just get on with it.

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While some climate economists have put the social cost of carbon at hundreds or even thousands of dollars per tonne of CO₂, one of the most influential analyses, by Yale University economist William Nordhaus, offers a much more modest figure of just over US$30.

Nordhaus won this year’s Nobel Prize in Economics, but his analysis has some uncomfortable conclusions for those familiar with the science.

At this level, it will be economically “optimal” for the world to reduce its CO₂ emissions quite slowly, so that global warming peaks at about 4℃ some time next century. But this certainly doesn’t sound optimal from a scientific perspective.

Reconstructed global mean temperature anomalies for 0–2000 CE, and DICE-2016R projections for 2015–2400.
CREDIT, Author provided

The impossibility of knowing the social cost of carbon

Calculating this magical economic balancing point is the holy grail of climate economics, and sadly it also seems to be an impossible task, because the question is so complex as to be unanswerable.

Why so? Normally, we gain knowledge via three main methods. The first option is to design an experiment. If that’s impossible, we can look for a similar case to observe and compare. And if that too is impossible, we can design a model that might hopefully answer our questions.

Generally, the laws of physics fall into the first category. It’s pretty straightforward to design an experiment to demonstrate the heat-trapping properties of CO₂ in a lab, for instance.

But we can’t do a simple experiment to assess the global effects of CO₂ emissions, so instead climatologists have to fall back on the second or third options. They can compare today’s conditions with previous fluctuations in atmospheric CO₂ to gauge the likely effects. They also design models to forecast future conditions on the basis of known physical principles.

By contrast, economists trying to put a dollar value on future climate damage face an impossible task. Like scientists, they cannot usefully test or make comparisons, but the economic effects of future climate change on an unprecedented 10 billion people are too fiendishly complex to model with confidence.

Unlike the immutable laws of physics, the laws of economics depend on markets, which in turn rely on trust. This trust could break down in some catastrophic future drought or deluge. So economists’ various rival calculations for the social costs of carbon are all based on unavoidable guesswork about the value of damage from unprecedented future warming.

This view is understandably unpopular with most climate economists. Many new studies claim that recent statistical techniques are steadily improving our estimates of the value of climate damage, based mainly on the local economic effects of short-run temperature and other weather changes in recent decades.

But so far, the world has experienced only about 1℃ of global warming, with at most 0.3℃ from one year to the next. That gives us almost no way of knowing the damage from warming of 3℃ or so; it may turn out to be many times worse than projected from past damage, as various tipping points are breached.

Focus on emission reduction, not damage cost

One reason why economists keep trying to value climate damage is a 1993 US Presidential Executive Order that requires cost-of-carbon estimates for use in US regulations. But my findings support what many other climate economists have been doing anyway. That is to build models that ignore the future dollar cost of climate damage, and instead look at feasible, low-cost ways to cut emissions enough to hit physical targets, such as limiting global warming to 1.5℃ or 2℃, or reaching zero net emissions by 2100.

Once we know these pathways, we don’t need to worry about the future cost of climate damage – all we need to ask is the cost of reducing emissions by a given amount, by a given deadline.

Of course, these costs are still deeply uncertain, because they depend on future developments in renewable energy technologies, and all sorts of other economic factors. But they are not as fiendishly uncertain as trying to pin a dollar value on future climate damage.

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Focusing on the cost of emissions-reduction pathways allows researchers to put their effort into practical issues, such as how far and fast countries can shift to zero-emission electricity generation. Countries such as Sweden and the UK have already begun implementing this kind of action-oriented climate policies. While far from ideal, they are among the best-ranked major economies in the Climate Change Performance Index. Australia, by contrast, is ranked third worst.

But aren’t trillion-dollar estimates of future warming damage, as featured in the recent US Fourth National Climate Assessment, necessary ammunition for advocates of climate action? Maybe, but it is still important to appreciate that these estimates are founded on a large chunk of guesswork.

Setting climate targets will always be a political question as well as a scientific one. But it’s an undeniably sensible aim to keep climate within the narrow window that has sustained human civilisation for the past 11,000 years. With that window rapidly closing, it makes sense for policymakers just to focus on getting the best bang for their buck in cutting emissions.

Jack Pezzey, Senior Fellow, Fenner School of Environment and Society, Australian National University

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

Native cherries are a bit mysterious, and possibly inside-out

John Tann/Flickr, CC BY-SA

Gregg Müller, La Trobe University

People don’t like parasites. But there’s a local Aussie tree that’s only a little bit parasitic: the native cherry, or cherry ballart.

It’s what we call hemiparasitic. It can photosynthesise, but gains extra nutrients by attaching its roots to host plants.

The native cherry, Exocarpos cupressiformis, might be our most widespread root hemiparasite tree, but we’re not quite sure – root-parasitic shrubs and trees are a bit of a research blank spot. We are not even really sure who all the hosts of cherry ballart are.

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Although other parasites – like mistletoes – have a more direct Christmas association, cherry ballart does have an Australian Yuletide connection: their conifer-like appearance (the species name cupressiformis means “cypress-like”) was noted by homesick European settlers, who chopped them down for Christmas trees.

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The Conversation

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On the map

Cherry ballart grows from the Atherton Tablelands in Queensland to southern Tasmania, and across to the Eyre Peninsula in South Australia.

The first European to record it was Jacques-Julien Houtou de Labillardière, the botanist on d’Entrecasteaux’s expedition in search of La Perouse. He formally described the species in 1800, but we have no physical type specimen – the botanical type is his illustration and description. Maybe he lost his specimen, or disposed of it, or thought a picture would do; Jacques seems to have been a bit cavalier with his record-keeping.

Or perhaps it was stolen or misplaced after all his specimens were seized in an overlapping series of defections, wars, defeats and revolution as the expedition tried to return to Europe. The collection was eventually returned after the intercession of English botanist Joseph Banks – but no cherry ballart.

Jacques-Julien Houtou de Labillardière’s description of the native cherry.
Voyage in search of La Pérouse

Its distinctive shape led to native cherry being marked on early Australian orienteering maps, since they are in a cartographic Goldilocks zone: obvious, just numerous enough to make them useful, but not so many as to clutter the map.

That was until Australia held the World Orienteering Championships in the mid-1980s, when the standardisation of Australian orienteering maps for overseas competitors led to the cherry ballart becoming an early victim of internationalisation – at least cartographically speaking.

Its utility also extended to the timber. Among the uses of its “close-grained and handsome wood” are tool handles, gun stocks and map rollers (although the last is probably a niche market these days).

Indigenous Australians ate the fruit, used the wood for spear throwers and reportedly used the sap as a treatment for snakebite. They called it Tchimmi-dillen (Queensland), Palatt or Ballot (Lake Condah, Victoria) and Ballee (Yarra).

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Grow baby, grow!

Despite producing large quantities of fruit and seed, no one seems to be able to get native cherry to germinate reliably. There are anecdotal reports that feeding the seed to chooks works, but other growers dismiss this approach.

The edible fruit isn’t actually a true fruit: it’s a swollen stem. It’s reported to have the highest sugar level of any native fruit in the forests of southern Victoria and is much tastier than you’d think a stem would be. (It’s also probably an important nutrient supply for some birds, but that’s yet another thing we are yet to prove.)

This odd “fruit” gives rise to the genus name (exo = outside, carpos = fruit,) and was often touted by early European writers as another example of the topsy-turvy nature of Australia – “cherries” with the pit on the outside went along with “duck-billed playtpus”, animals with pouches, trees that shed bark rather than leaves, and Christmas in the middle of summer.

The sweet and delicious fruit of native cherries is actually a swollen stem.
Arthur Chapman/Flickr, CC BY-NC

Despite their oddness, native cherries in the bush are biodiversity hotspots. My camera trap data show they preferentially attract echidnas, possums, foxes, swamp wallabies, white-winged choughs and bronzewing pigeons.

This might be because they modify their immediate environment. My research shows they create moderate micro-climates in their foliage, reduce soil temperatures, increase soil water retention, concentrate nutrients in the soil beneath their canopies, and alter the understorey vegetation. They also kill some of their host trees, creating patches with higher concentrations of dead timber. All these probably have something to do with their animal attraction, but exactly how is a mystery yet to be solved.

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In addition to their attractiveness to vertebrates, native cherries are required hosts for some striking moths and share specialist host duties with mistletoe for some of our most beautiful butterflies (although mistletoes take most of the glory in the scientific literature).

My research into our cherry ballart hopes in part to correct these historical slights. I want to set the record straight on this overlooked widespread and attractive little tree, which has a long indigenous use and was one of the first of our native flora to be described by Europeans.

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Sign up to Beating Around the Bush, a series that profiles native plants: part gardening column, part dispatches from country, entirely Australian.

Gregg Müller, Lecturer in Natural History, La Trobe University

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