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Shark nets are being trialled at five locations in northern New South Wales in response to a recent spate of shark attacks in this area.

The goal of these nets is to reduce the number of encounters of sharks with humans. The nets may do this by catching large sharks, and possibly by changing the way sharks visit these beaches.

There has been some doubt as to the effectiveness of shark nets in reducing attacks, so it’s important we continue to evaluate their role in bather protection.

But unfortunately it’s not as straightforward as it sounds, and it could take years to find out whether the nets will truly work.

Rare events

Shark attacks are very rare. According to the Australian Shark Attack File, 51 unprovoked attacks by white sharks have been recorded in NSW since 2006, 19 of them along the north coast (between Byron Bay and Evans Head).

There have undoubtedly been spikes in attacks over the last decade, especially in northern NSW, but the number of attacks has varied a lot between years and locations.

The problem is that when events (like shark encounters) are both rare and variable, it is very difficult to spot when there has been a genuine increase. And, crucially for the shark net trial, it is also difficult to tell whether policies are reducing them.

In the area of NSW where the shark nets will be trialled, between Broken Head and Evans Head, white shark attacks have ranged from zero to six per year in recent years. One way of getting an idea about how many attacks might occur in the future is to fit a statistical distribution to these data, and use this to predict the frequency at which attacks will occur (assuming the attack rate doesn’t change much).

In a hypothetical scenario in which the trialled shark nets are a success and reduce the attack rate by white sharks in the area by (say) 75%, our statistical distribution tells us that almost all years will have zero or one attack (see the red line below).

However, if the nets do nothing and the attack rate stays the same, we would still expect most years to have zero or one attack (the pink line below). This shows that it will be very difficult to know in the short term if the shark nets truly are reducing the risk of attack. This graph shows how difficult it can be to identify a reduction in risk, even by a large amount.

Even if there are zero attacks at a netted beach next year, that doesn’t necessarily tell us the net has worked, because statistically we would expect zero attacks in most years anyway. By the same token, if someone is bitten by a shark at one of the netted beaches, it doesn’t mean the nets aren’t effective. They may be greatly reducing the risk, just not eliminating it completely.

Because these encounters are so rare and variable, it will probably take years (rather than the six months planned for the trial) before there is enough evidence to show whether the nets have reduced attacks.

How and why

We also know very little about which factors influence encounters with large sharks. Without this information it is even harder to recognise whether the nets bring a decline in shark encounters.

In the above example, I used the recent history of attacks as the only guide to the future, but this is the most basic approach to exploring trends and assumes that recent history is a reliable indicator of the near future. A great way to improve this approach is to look for factors that can help explain why attacks vary between years – in essence basing our analysis on ecology rather than purely statistics.

The environment will almost certainly change the chance of a shark encounter. Factors like ocean temperature may have a big influence in determining when large sharks swim close to shore. The more of this “biological” information we have, the better we can account for variation in the number of shark attacks, and thus the better we will get at assessing whether policies like shark nets are working.

As described above, a six-month trial is not really long enough to learn anything meaningful about whether nets reduce shark attacks. It will provide other useful information, though, such as the likely impact on marine life. So we might find out whether the nets harm sharks, turtles, dolphins etc, but not whether they are making people any safer.

I am not suggesting that the trial won’t be useful – evaluating the impact on marine life is essential for assessing the costs of the nets. But what I am saying is that we need to avoid jumping to conclusions about whether they are “reducing the rate of unprovoked interactions with potentially dangerous sharks”. It will be years before we can attempt to answer that question.

In the meantime, there is much to be gained by increasing our understanding of how the environment influences shark distributions, by linking locations of tagged or caught sharks with the kinds of environments they inhabit. This will remove some of the guesswork in the “where and when” of shark attacks, and hopefully contribute to a more scientific approach to bather protection.

James Smith receives funding from the Australian Research Council to research coastal environments, including fish habitats and artificial reefs.

Progressive thinktank wants to know whether company will pay full coal royalties, full company tax rate and create jobs it claims

The progressive thinktank the Australia Institute is stepping up its campaign against the controversial Adani Carmichael mine proposal, publishing an open letter to Malcolm Turnbull questioning the project.

The questions being posed via a full-page advertisement in the Australian Financial Review on Wednesday include whether the Adani mine, if it proceeds, will pay full coal royalties to the Queensland government, or whether the project has been granted a royalty holiday.

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Donald Trump's plan to erect a huge sea wall at his Irish golf course have been withdrawn in the light of stiff opposition.

Alice Bell is right that we need to talk about climate change (Opinion, 6 December). However, when we do, people often say there is no point in cutting one’s own emissions (by not flying, for example) because hardly anyone else is; and they say there is no point in the UK doing anything, because other countries aren’t. Sadly, people in other countries are probably using the same arguments and so, in a self-fulfilling way, it could be argued that they are all correct. Certainly there is no evidence that nations or individuals are actually going to make the changes needed to cut greenhouse gas emissions adequately, whatever pledges may have been made at international conferences.

Clearly, we need a new approach: to invest in a combination of carbon scrubbing, geoengineering, third-way solutions, forest protection and reforestation. These can be funded by an international financial transactions tax, and they don’t involve lifestyle changes people won’t accept. We need to start now.
Richard Mountford
Hildenborough, Kent

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Glasgow Prestwick Airport signs an agreement with Houston Spaceport as it continues its bid to become the UK's first launch site.

A project is underway to record the underwater behaviour of Britain's grey seals.

Internet giant says renewable energy is increasingly lowest cost option and it will not rule out investing in nuclear power

Google’s data centres and the offices for its 60,000 staff will be powered entirely by renewable energy from next year, in what the company has called a “landmark moment”.

The internet giant is already the world’s biggest corporate buyer of renewable electricity, last year buying 44% of its power from wind and solar farms. Now it will be 100%, and an executive said it would not rule out investing in nuclear power in the future, too.

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A collection of zoological wonders from November 2016, featuring mobbing hyenas, speeding bats and crab power

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As global temperatures rise, extreme downpours will increase putting huge strains on infrastructure and agriculture, finds climate study

When the skies open up and deluge an area, the results can be catastrophic, with roads washed out and homes destroyed by the resulting flash floods. Such extreme downpours are already occurring more often across the US, but a new study finds that as global temperatures rise, storms could dump considerably more rain and skyrocket in frequency.

The study, in the journal Nature Climate Change, suggests that storms that now occur about once a season could happen five times a season by the century’s end, a 400% increase.

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Firefighters recover two cars from a sinkhole in Texas. An off-duty sheriff’s deputy died and two other people were hurt when two vehicles plunged into the water-filled sinkhole in San Antonio on Sunday. It appeared after a sewer line ruptured during heavy rain

• One dead after Texas sinkhole swallows two cars
  

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Stories of unusual insect activity are swarming across Australia, but is there any evidence to back up the reports?

England fells more trees than it plants and government must keep to its targets to evade deforestation, say forestry groups

Every year Brazil, Congo and other developing countries are lambasted by environmentalists and western politicians for deforestation at a time when trees are needed to counter climate change and prevent flooding.

Now two prestigious organisations are warning that England may have tipped into deforestation, with more trees being cut down than planted for the first time in possibly 40 years.

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Conspiracy websites and hyperpartisan media outlets are building huge online audiences who want to hear climate change is a hoax

Back in December 2015, Donald Trump gave a 30-minute live interview to the website Infowars.com and its combustible leader, Alex Jones.

“Your reputation is amazing and I will not let you down,” said Trump, who, at the time, was leading in most polls for the Republican presidential nomination.

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Claxton, Norfolk They rose and fell, swaying as if one organism were breathing slowly, and as they approached they never made sound

I saw the goose skein as a tentative line in a southern blue sky and, since it was arrowed straight towards me, I rested arms and binoculars on a gate to ease the muscle ache.

One, two minutes must have passed as the skein slowly grew, before it occurred to me that large birds in flight never rush. The wing beats are steady, solemn, self-reliant. I remember once in eastern Turkey watching a line of flamingos like this. There is an almost identical length of neck and leg fore and aft of those pink flamingo wings and, such was their lack of progress, it was a good five minutes before I could even work out in which direction they flew.

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BHP Billiton electricity supply agreement with existing NSW gas generator could open the path for the much touted solar tower and molten salt storage project.

Report finds Australia's shift to renewables, in line with its climate targets, would require significant inter-regional transmission upgrades, including a second link between Victoria and Tasmania by 2025.

Traditional hunting poses no threat to dugongs. Flickr, CC BY-SA

Recent calls for a ban on legal traditional hunting of dugongs and marine turtles imply that hunting is the main threat to these iconic species in Australia. The science indicates otherwise.

While more is being done to address traditional hunting than any of the other impacts, the main threats to their survival often pass unnoticed.

The real threat to sea turtles

The draft Recovery Plan for Marine Turtles in Australia evaluated 20 threats to the 22 populations of Australia’s six species of marine turtle. Climate change and marine debris, particularly “ghost nets” lost or abandoned by fishers, are the greatest risks for most stocks.

Indigenous use is considered to be a high risk for three populations: Gulf of Carpentaria green turtles, Arafura Sea flatback turtles and north-eastern Arnhemland hawksbill turtles.

However, in each of these cases it is the egg harvest, not hunting, that causes concern. International commercial fishing is also a high risk for the hawksbill turtle, whose future remains uncertain. Traditional hunting of marine turtles in Australia is limited to green turtles.

Is hunting a threat?

The Torres Strait supports the largest dugong population in the world and a globally significant population of green turtles. Archaeological research shows that Torres Strait Islanders have been harvesting these species for more than 4,000 years and the dugong harvest has been substantial for several centuries.

Our research shows that the Torres Strait dugong population has been stable since we started monitoring 30 years ago and that the harvest of both species is sustainable.

The situation for dugongs is very different in the waters of the Great Barrier Reef south of Cooktown. The Great Barrier Reef Outlook Report classifies the condition of the dugong population in this region as poor.

Modelling indicates that the southern Great Barrier Reef stock of the green turtle, which live and breed south of Cooktown, is increasing.

Nonetheless, both green turtles and dugongs died in record numbers in the year after the extreme floods and cyclones of the summer of 2010-11. Dugongs stopped breeding in the Great Barrier Reef region south of Cooktown.

Thankfully, our current aerial survey indicates that dugong calving has resumed as inshore seagrass habitats recover. There is no evidence that the 2011 losses significantly affected green turtle numbers.

Working together

Traditional owners are the first managers of our coastal waters, with cultural practices extending back thousands of years. They have the most to lose from any loss of turtles and dugongs. It is therefore in their best interests, and the government’s best interest, to work in partnership to protect and sustainably manage these species.

Longstanding tensions between traditional owners and tourist operators are behind much of the opposition to traditional hunting in the Cairns area. Some of these tensions have been relieved by the Gunggandji Traditional Use of Marine Resources Agreement signed in June 2016.

Under this agreement, the traditional owners decided to cease hunting turtles and dugongs in the waters surrounding Green Island, Michaelmas Cay and Fitzroy Island.

The Gunggandji agreement is the seventh to be signed between the Great Barrier Reef Marine Park Authority and traditional owners. In addition, there are two Indigenous land use agreements that address hunting issues in the Great Barrier Reef.

In the Torres Strait, dugong and turtle hunting is managed through 14 (soon to be 15) management plans. There are similar agreements with traditional owners and management agencies in other regions in northern Australia.

Indigenous rangers are crucial to implementing all these agreements in collaboration with management agencies and research institutions. Rangers deliver the practical, on-the-ground arrangements to conserve these species in their Sea Country.

The Great Barrier Reef Marine Park Authority has implemented an Indigenous Compliance Program that authorises trained Indigenous rangers to respond to suspicious and illegal activities that they encounter as part of their work.

Indigenous rangers and community members from Badu Island in Torres Strait help JCU scientists fit a dugong with a satellite tracking device. Takahiro Shimada/James Cook University

Indigenous rangers also remove marine debris from remote beaches. The community-based organisation GhostNets Australia has worked with 31 coastal Indigenous communities to protect over 3,000km of northern Australia’s saltwater country from ghost nets. These community projects have been instrumental in rescuing turtles, clearing ghost nets off beaches and identifying key areas to aid management agencies to better understand the impact.

Traditional owners from the Torres Strait and the northern Great Barrier Reef also play a valuable role in intervention works at Raine Island, one of the world’s most significant green turtle rookeries. This includes rescuing stranded turtles, using fences to stop turtles from falling over cliffs, and altering beach profiles.

What about welfare?

Traditional hunting raises animal welfare issues. The turtle and dugong management plans developed by the Torres Strait communities explicitly address animal welfare. The Torres Strait Regional Authority has been working with a marine mammal veterinarian and traditional owners to develop additional methods of killing turtles humanely.

Indigenous hunters who breach state and territory animal welfare laws can be prosecuted. But more widespread animal welfare problems, not associated with hunting, are largely hidden and ignored. The Queensland Strand Net Program reported that 879 turtles died of their wounds from vessel strike between 2000 and 2011.

An immature female loggerhead turtle severely injured by a boat strike near Gladstone. This turtle was determined to be unrecoverable and was euthanased by a local veterinarian in May 2016. Takahiro Shimada/James Cook University

Other serious animal welfare issues are associated with animals drowning in nets and being caught in and ingesting marine debris. In addition, the potential impact of emerging threats like underwater noise pollution and water quality remain as substantial knowledge gaps. These matters tend not to make the headlines.

Australian waters are home to some of the world’s largest populations of marine turtles and dugongs. A comprehensive and balanced approach to their conservation and management is required to enable our grandchildren and their children to enjoy these amazing animals.

Helene Marsh FAA, FTSE, Distinguished Professor of Environmental Science at James Cook University, is a conservation biologist who has been studying dugongs for 40 years. She has co-authored two books and some 200 professional articles. Helene currently receives funding from the federal government via the Australian Research Council, the Department of Environment and Energy, the National Environmental Science Program and the Great Barrier Reef Marine Park Authority. She provides professional advice to the Torres Strait Regional Authority, the Great Barrier Reef Marine Park Authority. Helene chairs the Threatened Species Scientific Committee, is a member of the Reef 2050 Plan Independent Expert Panel and Co–chair of the IUCN Sirenia Specialist Group. https://research.jcu.edu.au/portfolio/helene.marsh/

Mark Haman is an Associate Professor in the College of Science and Engineering at James Cook University. He currently receives funding from the federal government via the Australian Research Council and the National Environmental Science Program and from the Gladstone Port Authority. Mark provides professional advice to the Torres Strait Regional Authority, the Great Barrier Reef Marine Park Authority, the Department of Environment and Energy and the Queensland Government. Mark is a Co-vice Chair of the IUCN Marine Turtle Specialist Group and a member of the Science Advisory Committee for the IOSEA MoU for Marine Turtles and their Habitats.

Analysts says $1bn loan proposal shows lack of financier interest and Adani may not meet investment criteria due to position that public funding ‘not critical’

Doubts have emerged over the eligibility of Adani’s rail link for public funding as the company pushes ahead with plans for the controversial Carmichael coal project with a promise of 600 jobs at a new operational headquarters in Townsville.

The Queensland premier, Annastacia Palaszczuk, said “you can’t get the smile off my face” when commenting on the news of the potential jobs boost in a television interview.

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Origin Energy reveals plan to float its upstream oil and gas business, to focus CSG and energy markets. But it stopped short of fossil fuel exit.

Australia’s monopoly electricity networks are the most profitable businesses in Australia. And the consumer pays, and pays.