A landmark new study published today in Nature by Global FinPrint reveals sharks are virtually absent on many of the world’s coral reefs. Sharks were not observed on nearly 20 percent of the 371 reefs surveyed in 58 countries, indicating a widespread decline that has largely gone undocumented until this global survey.
Fortunately, Australia is a country where shark populations on coral reefs are still largely intact. The most common shark species observed were grey reef, whitetip reef and blacktip reef sharks.
Dr Mark Meekan, from the Australian Institute of Marine Science in Perth and Principal Investigator for the Global FinPrint project in the Indian Ocean region said good management plays a key role in determining the status of reef sharks. “Our survey not only reveals the plight of sharks on coral reefs, which is in many cases very worrying, it also reveals how control of shark fishing can make effective conservation gains,” Dr Meekan said. Australia was one of several nations where the study revealed that shark conservation on coral reefs is working. Other nations include the Bahamas, the Federated States of Micronesia, French Polynesia, the Maldives, and the United States. Dr Meekan said reef sharks play an important role maintaining a healthy ecosystem. “Sharks are important for the ecology of coral reefs, particularly at a time when they are facing so many other threats from climate change. But few people realise that reef sharks are also an important part of the economies of many small island nations around the world because they are a key attraction for reef tourism. “Rebuilding shark numbers isn’t just good sense ecologically – it also makes good sense economically,” Dr Meekan said.
AIMS scientist Dr Michelle Heupel, and Global FinPrint Principal Investigator in the Western Pacific, said this world first study relied on cooperation and collaboration of colleagues in many nations and territories across the globe. “Hundreds of scientists, researchers, and conservationists captured and analysed more than 15,000 hours of video from surveys of 371 reefs in 58 countries, states and territories around the world over four years. “We hope these findings will help countries continue to maintain shark populations or make management changes to improve their status,” she said. Funded by the Paul G. Allen Family Foundation, the Global FinPrint’s survey data were generated from baited remote underwater video systems (BRUVS) consisting of an underwater video camera attached to a bait bag containing a small amount of fish. Coral reef ecosystems were surveyed with BRUVS in four key geographic regions: The Indo-Pacific, Pacific, the Western Atlantic and the Western Indian Ocean. As well as AIMS, other coordinating organisations working on the project came from Florida International University, Curtin University, Dalhousie University, and James Cook University.
For more information and a new global interactive data-visualized map of the Global FinPrint survey results, visit https://globalfinprint.org.
23 July 2020
Scientists have discovered a significant coral bleaching event at one of Western Australia’s healthiest coral reefs.
More than 250 kilometres west of Broome, the Rowley Shoals is one of only two reef systems in the State to have recorded high and stable coral cover throughout the past decade.
In April and May 2020, the Australian Institute of Marine Science (AIMS) and the Department of Biodiversity, Conservation and Attractions (DBCA) conducted surveys of the reef system, supported by Parks Australia and Australian Border Force, to confirm reports of significant coral bleaching.
Data obtained revealed that bleaching was variable across the Rowley Shoals, with estimates ranging between one and 30 percent of the corals bleached. One site on Clerke Reef experienced up to 60 percent of the corals bleached. Further aerial surveys of the North Kimberley and Lalang-garram marine parks found coral bleaching to be patchy and less severe than at Rowley Shoals.
Following temperature alerts issued by the Bureau of Meteorology (BOM), aerial flights by Australian Border Force provided the first evidence of coral bleaching at Western Australia’s remote coral reef atolls Image: Australian Border Force DBCA’s Marine Monitoring Coordinator Dr Thomas Holmes attributed the bleaching to an unusually warm and prolonged ocean temperature off the coast of the Kimberley. “By global standards, Western Australia still has relatively healthy reefs, but seawater temperature is increasing around the world as a result of climate change. This is causing corals to bleach and die from heat stress more frequently and at scales not previously observed,” Dr Holmes said.
The extent and severity of bleaching varied across the Rowley Shoals, ranging from 10% to over 60% bleaching at some sites. Image: Chris Tucker
AIMS’ coral ecologist Dr James Gilmour said that bleaching had badly affected other offshore atolls and the inshore Kimberley region in 2016/17. “Coral bleaching can devastate entire reef systems and dramatically alter associated communities of marine plants and animals,” Dr Gilmour said. “Some corals will regain their symbiotic algae and recover, while those corals that have been severely bleached are likely to die.”
At the worst affected sites, even the robust massive corals at 20m depth had bleached. Image: Chris Tucker
Follow up surveys as a part of DBCA and AIMS long-term monitoring programs are currently planned for later this year to determine the full effect of the event on the coral communities. The bleaching survey of Rowley Shoals was conducted as part of AIMS’ North West Shoals to Shore Research Program funded by Santos Ltd.
14 July 2020
A new study published in the journal PeerJ by researchers at the University of Hawaii found that human-induced environmental stressors have a large effect on the genetic composition of coral reef populations in Hawaii.
The National Science Foundation-funded scientists confirmed that there is an ongoing loss of sensitive genotypes in nearshore coral populations due to stressors from poor land-use practices and coastal pollution. This reduced genetic diversity compromises reef resilience.
This research provides valuable information to coral reef managers in Hawaii and around the world who are developing approaches and implementation plans to enhance coral reef resilience and recovery through reef restoration and stressor reduction.
The study identified that genetic relationships between nearshore corals in Maunalua Bay, Oahu, and those from sites on West Mau were closer than relationships to corals from the same islands, but farther offshore.
This pattern can be described as isolation by environment in contrast to isolation by distance. This is an adaptive response by the corals to watershed discharges that contain sediment and pollutants from land.
“While the results were not surprising, they demonstrate the need to control local sources of stress while addressing the root causes of global climate change,” said Robert Richmond, director of the Kewalo Marine Laboratory and co-author of the study. “The findings show the need to track biodiversity at multiple levels.”
While the loss of coral colonies and species is easy to see with the naked eye, molecular tools are needed to uncover the effects of stressors on the genetic diversity within coral reef populations. “This study shows the value of applying molecular tools to ecological studies supporting coral reef management,” stated Kaho Tisthammer, lead researcher on the paper.
The work was a collaborative effort among researchers at the university’s Kewalo Marine Laboratory, Pacific Biosciences Research Center, and the Hawaii Institute of Marine Biology. “This work highlights the importance of limiting pollution, sediment, and agricultural runoff to nearshore coral reefs,” says Dan Thornhill, a program director in NSF’s Division of Ocean Sciences. “Protecting biodiversity is essential, as that diversity is needed in helping corals and other marine life adapt to changing oceans. Selecting for resilience to pollution may eliminate coral genotypes that resist disease, tolerate higher temperatures, and continue to grow in more acidic and oxygen-depleted waters.”
9 April 2020
Currents are strong around the Torres Strait Islands, lying between Australia’s northern-most tip and Papua New Guinea. When the tidal conditions are right and the waters relatively still, though, up to 230 islanders – a sizeable percentage of the islands’ roughly 4,000 indigenous inhabitants – will board small boats and head out to the surrounding reefs. There they will dive down and search the underwater outcrops for lobsters, grabbing the crustaceans by hand. It’s laborious work compared with lobster fishing in other parts of Australia, where fishers bait “pots”, then simply pull up the pots with lobsters inside. The tropical rock lobsters of the Torres Strait, however, are sensitive creatures and generally won’t crawl into a trap. By hand is the only sure way to catch them. But, until a few weeks ago, it has been worth it. A fisher can sell a live lobster from these waters for $65-95 a kilogram. That makes it worth holding them in water-filled crates and then flying them to wholesalers in Cairns. There they are processed and transported to domestic and international markets.
The most lucrative market is China. Its appetite for live rock lobster makes up about half the value of Australia’s seafood exports (A$660 million of A$1.4 billion). Now, though, lobster fishers are staying home. There hasn’t been a regular lobster shipment to China since January 26. With the Wuhan coronavirus suspected to have originated from wild animals in the city’s Huanan Seafood Wholesale Market, Chinese authorities have temporarily banned all wild animal trade. Lobster and other wild-caught aquatic products are exempt from the ban, but demand has plummeted due to people staying home and avoiding both markets and restaurants.This collapse has come at a time that would normally be one of peak demand, and peak prices, due to Chinese New Year festivities. Our industry sources report prices for live lobsters are down 50% to 80%.
It’s a huge blow to the economy of Torres Strait, along with the rest of Australia’s live seafood export industry.
Lobster fishing is among the highest-value economic activities in the strait. Indigenous islanders have limited alternatives to make money, given their geographical isolation. As scientists fortunate to work closely with traditional owners in the Torres Strait over the past decade, we’re saddened to see this devastating impact on livelihoods.
CSIRO researchers have worked in the strait for more than three decades to help local people sustain their traditional way of life and conserve the marine environment for future generations. This is no easy feat, considering the resources are also shared with an Australian non-Islander sector and traditional owners from Papua New Guinea. The region’s wild marine fisheries have been thriving thanks to good management and a strong sense of custodianship by the Islanders.
New harvest strategies for fishing lobster and bêche-de-mer (sea cucumbers) were implemented in December 2019. These took years of research and consultation. This included augmenting scientific surveys with information from fishers to work out sustainable catches. The new strategies followed a disastrous lobster-fishing year in 2018, when our scientific surveys suggested the lobster population was in trouble due to conditions created by extreme El Niño events. The fishery had to be closed two months early, with substantial economic impact. It was nonetheless an example of Torres Strait Islanders putting sustainability before short-term gain.
Now they have the coronavirus to contend with. The loss of income from those in the fishing business affects other small businesses and ripples throughout the local community. Selling to the frozen seafood market is an option, but prices are much lower, and there’s a point at which the time, effort and cost of catching a tropical rock lobster make it uneconomical. Boat fuel, for one thing, is expensive. Sales of frozen seafood to China have also taken a dive. For some Australian fisheries it’s possible taking fewer fish this season will mean a larger fish population next year. So next year’s catch quotas could be adjusted up without jeopardising the marine population. This could partially offset losses this year. But that’s not an option for the Torres Strait lobster fishery. That’s because by the time a lobster is big enough to catch, usually in its third year of life, it is also ready to migrate, walking several hundred kilometres to the east of the fishery area. So catching fewer lobsters this year won’t mean they are around to catch next year. It is a unique fishery in this regard.
This impact of the coronavirus on Torres Strait Islanders shows how connected global trade now is. What it also demonstrates is the importance of deliberate and distributed growth in export markets for them to be sustainable. Heavy dependence on a single market carries a big risk. As things stand, we can expect demand for seafood in China will remain low for some time to come. This is an opportune time to rethink sustainable export growth strategies.
19 February 2020
As Australians look forward to the summer beach season, the prospect of shark encounters may cross their minds. Shark control has been the subject of furious public debate in recent years and while some governments favour lethal methods, it is the wrong route.
Our study, published today in People and Nature, presents further evidence that lethal shark hazard management damages marine life and does not keep people safe.
We examined the world’s longest-running lethal shark management program, the New South Wales Shark Meshing (Bather Protection) Program, introduced in 1937. We argue it is time to move on from shark nets and invest further in lifeguard patrol and emergency response.
In NSW, 51 beaches between Newcastle and Wollongong are netted. The nets don’t provide an enclosure for swimmers. They are 150 metres long and suspended 500 metres offshore. In the process of catching targeted sharks they also catch other animals including turtles, rays, dolphins, and harmless sharks and fish.
Catching and killing sharks might seem a commonsense solution to the potential risk of shark bite to humans. But the story is not so simple.
Multiple factors influence shark bite incidence, including climate change, prey species distribution and abundance, water quality, human population, beach-use patterns, and lifeguard patrols.
Most research and public debate focuses on human safety or marine conservation. Our research sought to bring the two into conversation. We considered a range of factors that contribute to safety and conservation outcomes. This included catch of target and non-target species in nets, damage to marine ecosystems, global pressures on oceans, changing beach culture, human population growth and changes in lifeguarding and emergency response. Here’s what we found.
As the graph below shows, shark catch in the NSW netting program has fallen since the 1950s. This includes total shark numbers and numbers of three key target species: white shark (also known as great white or white pointer), tiger shark and bull shark.
Our analysis shows shark bite incidence is also declining over the long term. The trend isn’t smooth; trends rarely are. The last two decades have seen more shark bites than the previous two. This is not surprising given Australia’s beach use has again grown rapidly in recent decades.
But if we take a longer term view, we see that shark bite incidence relative to population is substantially lower from the mid-20th century than during the decades before.
The decline in shark bite incidence is great news. But key points are frequently overlooked when society tries to make sense of the figures.
In NSW, lifeguard beach patrol grew over the same time period as the shark meshing program. More people swam and surfed in the ocean from the early 20th century as public bathing became legal. The surf lifesaving and professional lifeguard movements grew rapidly in response.
Today, 50 of the 51 beaches netted through the shark meshing program are also patrolled by lifeguards or lifesavers. Yet improved safety is generally attributed to the mesh program. The role of beach patrol is largely overlooked.
So, claims that shark bite has declined at netted beaches might instead be interpreted as decline at patrolled beaches. In other words, reduced shark interactions may be the result of beach patrol.
More good news is that since the mid-20th century the proportion of shark bites leading to fatality has plummeted. This is most likely the result of enormous improvements in beach patrol, emergency and medical response.
Debate over shark management is often polarised, pitting human safety against marine conservation. We have brought together expertise from the social sciences, biological sciences and fisheries, to move beyond a “people vs sharks” debate.
There is no reliable evidence that lethal shark management strategies are effective. Many people oppose them, institutions are moving away from them, and threatened species are put at risk.
The NSW Department of Primary Industries, manager of the shark meshing program, is investing strongly in new non-lethal strategies, including shark tagging, drone and helicopter patrol, personal deterrents, social and biophysical research and community engagement. Our study provides further evidence to support this move.
Investing in lifeguard patrol and emergency response makes good sense. The measures have none of the negative impacts of lethal strategies, and are likely responsible for the improved safety we enjoy today at the beach.
Leah Gibbs, Senior Lecturer in Geography, University of Wollongong; Lachlan Fetterplace, Environmental Assessment Specialist, Swedish University of Agricultural Sciences, and Quentin Hanich, Associate Professor, University of Wollongong
4 December 2019
A Sea Shepherd beach clean-up campaign in Northeast Arnhem Land has further exposed the catastrophic impact of marine plastic pollution on mainland Australia.
The Shocking Reality
Over seven tonnes of marine plastic pollution was removed by ten volunteers from Sea Shepherd Australia and Indigenous Rangers from the Dhimurru Aboriginal Corporation in a two-week-long collaboration at Djulpan Beach on the shores of the Gulf of Carpentaria, Northern Territory.
During the campaign, Sea Shepherd conducted scientific surveys across the 14-kilometre stretch of beach in collaboration with marine plastic pollution expert Dr Jennifer Lavers.
Findings from the surveys concluded that there were an estimated 250 million pieces of marine debris present.
Untrashing Djulpan: the Campaign
So remote and untouched by human contact is Djulpan Beach, Rangers cut a 4WD track from the nearest road to allow access for vehicles and equipment. The volume and density of plastic pollution removed from Djulpan was at a scale that the Sea Shepherd volunteers had not seen before on a mainland Australian beach, despite having facilitating over 600 clean-ups in the past three years.
Around 4.5 tonnes of the debris removed were consumer items including:
● plastic lids, tops and pump sprays (14494 pieces)
● plastic drink bottles (6054 pieces)
● cigarette lighters (3344 pieces
● personal care and pharmaceutical packaging (4881 pieces)
● thongs (3769 pieces)
● toothbrushes, hair brushes and hair ties (775 pieces) and
● toys such as chess pieces (64 pieces)
In many cases, the plastic items were so degraded that when volunteers went to pick them up, they crumbled into plastic dust.
The remaining 2.5 tonnes was made up of 72 different types of discarded fishing nets or ghost nets, some of which contained turtle bones.
Hundreds of plastic items were found with multiple animal bites, including those from fish and turtles. The stretch of coast that Djulpan is located on is home to six of the seven species of marine turtles which are all listed as ‘Vulnerable’ or ‘Endangered’ under the Environmental Protection and Biodiversity Conservation (EPBC) Act
Much of the trash found along Cape Arnhem originates from ocean currents and trade winds above Australia that pushes the debris into the Gulf of Carpentaria in a clockwise direction before washing ashore.
“The marine debris littering our beaches saddens us. Not only is it killing our turtles and other marine life, it also pollutes some of our sacred areas. The rangers work hard to try and keep the beaches clean, but we need to stop the rubbish going into the ocean in the first place.” -- Managing Director of the Dhimurru Aboriginal Corporation Mandaka Marika.
“What we found when we arrived at the beach on day one looked like something out of Armageddon, with plastic pieces visible across the entire beach as far as the eye could see. This campaign clearly shows that even in a remote place like Arnhem Land, that nowhere is safe from human-induced plastic pollution” -- Sea Shepherd Australia’s National Marine Debris Coordinator Liza Dicks.
What can you do?
Australia simply cannot turn a blind eye to the impacts that plastic pollution is having – whether it be on Australian shores or at the regional or global level. We need to come together and act now as a collective to ensure there is a solution to this increasing global environmental issue.
First published by SeaShephard: https://www.seashepherd.org.au/latest-news/untrashing-djulpan/
22 Sep 2019
The rise in sea levels is not the only way climate change will affect the coasts. Our research, published today in Nature Climate Change, found a warming planet will also alter ocean waves along more than 50% of the world’s coastlines.
If the climate warms by more than 2℃ beyond pre-industrial levels, southern Australia is likely to see longer, more southerly waves that could alter the stability of the coastline.
Scientists look at the way waves have shaped our coasts – forming beaches, spits, lagoons and sea caves – to work out how the coast looked in the past. This is our guide to understanding past sea levels.
But often this research assumes that while sea levels might change, wave conditions have stayed the same. This same assumption is used when considering how climate change will influence future coastlines – future sea-level rise is considered, but the effect of future change on waves, which shape the coastline, is overlooked.
Waves are generated by surface winds. Our changing climate will drive changes in wind patterns around the globe (and in turn alter rain patterns, for example by changing El Niño and La Niña patterns). Similarly, these changes in winds will alter global ocean wave conditions.
Further to these “weather-driven” changes in waves, sea level rise can change how waves travel from deep to shallow water, as can other changes in coastal depths, such as affected reef systems.
Recent research analysed 33 years of wind and wave records from satellite measurements, and found average wind speeds have risen by 1.5 metres per second, and wave heights are up by 30cm – an 8% and 5% increase, respectively, over this relatively short historical record.
These changes were most pronounced in the Southern Ocean, which is important as waves generated in the Southern Ocean travel into all ocean basins as long swells, as far north as the latitude of San Francisco.
Given these historical changes in ocean wave conditions, we were interested in how projected future changes in atmospheric circulation, in a warmer climate, would alter wave conditions around the world.
As part of the Coordinated Ocean Wave Climate Project, ten research organisations combined to look at a range of different global wave models in a variety of future climate scenarios, to determine how waves might change in the future.
While we identified some differences between different studies, we found if the 2℃ Paris agreement target is kept, changes in wave patterns are likely to stay inside natural climate variability.
However in a business-as-usual climate, where warming continues in line with current trends, the models agreed we’re likely to see significant changes in wave conditions along 50% of the world’s coasts. These changes varied by region.
Less than 5% of the global coastline is at risk of seeing increasing wave heights. These include the southern coasts of Australia, and segments of the Pacific coast of South and Central America.
On the other hand decreases in wave heights, forecast for about 15% of the world’s coasts, can also alter coastal systems.
But describing waves by height only is the equivalent of describing an orchestra simply by the volume at which it plays.
Some areas will see the height of waves remain the same, but their length or frequency change. This can result in more force exerted on the coast (or coastal infrastructure), perhaps seeing waves run further up a beach and increasing wave-driven flooding.
Similarly, waves travelling from a slightly altered direction (suggested to occur over 20% of global coasts) can change how much sand they shunt along the coast – important considerations for how the coast might respond. Infrastructure built on the coast, or offshore, is sensitive to these many characteristics of waves.
While each of these wave characteristics is important on its own, our research identified that about 40% of the world’s coastlines are likely to see changes in wave height, period and direction happening simultaneously.
While some readers may see intense waves offering some benefit to their next surf holiday, there are much greater implications for our coastal and offshore environments. Flooding from rising sea levels could cost US$14 trillion worldwide annually by 2100 if we miss the target of 2℃ warming.
How coastlines respond to future climate change will be a response to a complex interplay of many processes, many of which respond to variable and changing climate. To focus on sea level rise alone, and overlooking the role waves play in shaping our coasts, is a simplification which has great potential to be costly.
The authors would like to acknowledge the contribution of Xiaolan Wang, Senior Research Scientist at Environment and Climate Change, Canada, to this article.
Mark Hemer, Principal Research Scientist, Oceans and Atmosphere, CSIRO; Ian Young, Kernot Professor of Engineering, University of Melbourne; Joao Morim Nascimento, PhD Candidate, Griffith University, and Nobuhito Mori, Professor, Kyoto University
20 Aug 2019
One hectare of ocean in which fishing is not allowed (a marine protected area) produces at least five times the amount of fish as an equivalent unprotected hectare, according to new research published today.
This outsized effect means marine protected areas, or MPAs, are more valuable than we previously thought for conservation and increasing fishing catches in nearby areas.
Previous research has found the number of offspring from a fish increases exponentially as they grow larger, a disparity that had not been taken into account in earlier modelling of fish populations. By revising this basic assumption, the true value of MPAs is clearer.
Marine protected areas are ocean areas where human activity is restricted and at their best are “no take” zones, where removing animals and plants is banned. Fish populations within these areas can grow with limited human interference and potentially “spill-over” to replenish fished populations outside.
Obviously MPAs are designed to protect ecological communities, but scientists have long hoped they can play another role: contributing to the replenishment and maintenance of species that are targeted by fisheries.
Wild fisheries globally are under intense pressure and the size fish catches have levelled off or declined despite an ever-increasing fishing effort.
Yet fishers remain sceptical that any spillover will offset the loss of fishing grounds, and the role of MPAs in fisheries remains contentious. A key issue is the number of offspring that fish inside MPAs produce. If their fecundity is similar to that of fish outside the MPA, then obviously there will be no benefit and only costs to fishers.
Traditional models assume that fish reproductive output is proportional to mass, that is, doubling the mass of a fish doubles its reproductive output. Thus, the size of fish within a population is assumed to be less important than the total biomass when calculating population growth.
But a paper recently published in Science demonstrated this assumption is incorrect for 95% of fish species: larger fish actually have disproportionately higher reproductive outputs. That means doubling a fish’s mass more than doubles its reproductive output.
When we feed this newly revised assumption into models of fish reproduction, predictions about the value of MPAs change dramatically.
Fish are, on average, 25% longer inside protected areas than outside. This doesn’t sound like much, but it translates into a big difference in reproductive output – an MPA fish produces almost 3 times more offspring on average. This, coupled with higher fish populations because of the no-take rule means MPAs produce between 5 and 200 times (depending on the species) more offspring per unit area than unprotected areas.
Put another way, one hectare of MPA is worth at least 5 hectares of unprotected area in terms of the number of offspring produced.
We have to remember though, just because MPAs produce disproportionately more offspring it doesn’t necessarily mean they enhance fisheries yields.
For protected areas to increase catch sizes, offspring need to move to fished areas. To calculate fisheries yields, we need to model – among other things – larval dispersal between protected and unprotected areas. This information is only available for a few species.
We explored the consequences of disproportionate reproduction for fisheries yields with and without MPAs for one iconic fish, the coral trout on the Great Barrier Reef. This is one of the few species for which we had data for most of the key parameters, including decent estimates of larval dispersal and how connected different populations are.
We found MPAs do in fact enhance yields to fisheries when disproportionate reproduction is included in relatively realistic models of fish populations. For the coral trout, we saw a roughly 12% increase in tonnes of caught fish.
There are two lessons here. First, a fivefold increase in the production of eggs inside MPAs results in only modest increases in yield. This is because limited dispersal and higher death rates in the protected areas dampen the benefits.
However the exciting second lesson is these results suggest MPAs are not in conflict with the interests of fishers, as is often argued.
While MPAs restrict access to an entire population of fish, fishers still benefit from from their disproportionate affect on fish numbers. MPAs are a rare win-win strategy.
It’s unclear whether our results will hold for all species. What’s more, these effects rely on strict no-take rules being well-enforced, otherwise the essential differences in the sizes of fish will never be established.
We think that the value of MPAs as a fisheries management tool has been systematically underestimated. Including disproportionate reproduction in our assessments of MPAs should correct this view and partly resolve the debate about their value. Well-designed networks of MPAs could increase much-needed yields from wild-caught fish.
July 4 2019
Hundreds of juvenile corals bred at the Australian Institute of Marine Science (AIMS) have survived being transplanted on the Great Barrier Reef, in a promising early test to help corals increase their resilience to marine heatwaves. The trial aims to show young coral offspring produced from mixing corals from warm northern reefs, with cooler central corals, can survive in cooler environments. This is the first test to assess the feasibility of the technique called Assisted Gene Flow at this larger scale on the Great Barrier Reef. The seven-month-old corals have one parent from the warmer northern reaches of the Reef and the other from the cooler central Reef.
AIMS marine scientist Dr Kate Quigley says research has shown the offspring inherit heat tolerance from their northern parents, and in time, they may pass on these heat tolerant genes and make reefs more resistant to future marine heat waves. “Last year we collected corals from the far north of the Great Barrier Reef that survived previous heat waves, and we flew them nearly 1000km to AIMS in Townsville,” Dr Quigley said.
“We have cross-fertilised them with corals from the middle of the Reef to see if the heat tolerance is passed on.”
Dr Line Bay, who leads AIMS’ research into reef recovery, adaptation and restoration, said Assisted Gene Flow, was helping nature to do what it does naturally, and is one of several techniques being developed at AIMS to help coral survive higher future ocean temperatures in coming decades. “When corals get too hot they are damaged and bleach, and this can lead to extensive mortality as we have recently seen on the Great Barrier Reef,” Dr Bay said. “If corals are to persist into the future, they have to cope with these increasing temperatures, and because of the rate of warming, they will have to become more tolerant fast. “We are focussed on developing new solutions for managing our coral reefs in a warming future.”
AIMS researchers took the same species of corals from three sites in the northern region, and two sites on the central Great Barrier Reef and cross-fertilised them in climate-controlled tanks at the National Sea Simulator in Townsville, to produce dozens of distinct genetic crosses. The National Sea Simulator is the world’s most advanced research aquarium. These crosses were then settled onto terracotta tiles and moved to a site on the Great Barrier Reef, in March.
This first expedition to check on these coral juveniles has just returned, and researchers are analysing the results. “We found many of the warm-adapted corals have survived the now quite cool waters of the central Reef,” Dr Quigley said. “This early result supports further testing of Assisted Gene Flow as a management action tool for corals in a warming future.” The field tests will add to results from experiments in the National Sea Simulator which showed these juvenile corals with at least one parent from the far northern Great Barrier Reef, are significantly more likely to survive high temperatures. AIMS researchers plan to return to the test site in October to check in again on how the corals are growing and surviving.
This research is partly funded by the partnership between the Australian Government’s Reef Trust and the Great Barrier Reef Foundation.
First published by AIMS July 2 2019
As concern grows over human-induced climate change, many scientists are looking back through Earth’s history to events that can shed light on changes occurring today. Analyzing how the planet’s climate system has changed in the past improves our understanding of how it may behave in the future.
It is now clear from these studies that abrupt warming events are built into Earth’s climate system. They have occurred when disturbances in carbon storage at Earth’s surface released greenhouse gases into the atmosphere. One of the grand challenges for climate scientists like me is to determine where these releases came from before humans were present, and what triggered them. Importantly, we want to know if such an event could happen again.
In a recently published study, my colleagues Katie Harazin, Nadine Krupinski and I discovered that at the end of the last glacial era, about 20,000 years ago, carbon dioxide was released into the ocean from geologic reservoirs located on the seafloor when the oceans began to warm.
This finding is a potential game-changer. Naturally occurring reservoirs of carbon in the modern ocean could be disturbed again, with potentially serious effects to Earth’s oceans and climate.
One of the best-known examples of a rapid warming caused by release of geologic carbon is the Paleocene-Eocene Thermal Maximum, or PETM, a major global warming event that occured about 55 million years ago. During the PETM, the Earth warmed by 9 to 16 degrees Fahrenheit (5 to 9 degrees Celsius) within about 10,000 years.
Climate scientists now consider the PETM to be an analog for environmental changes taking place today. The PETM happened over a longer period and without human involvement, but it shows that there is inherent instability in the climate system if carbon from geologic reservoirs is released rapidly.
Scientists also know that atmospheric carbon dioxide levels rose rapidly at the end of each of the late Pleistocene ice ages, helping to warm the climate. During the most recent warming episode, 17,000 years ago, the Earth warmed by 9 to 13 degrees Fahrenheit (5 to 7 degrees Celsius).
However, hundreds of scientific studies have failed to establish what caused the rapid carbon dioxide increases that ended each ice age. Researchers agree that the ocean must be involved because it acts as a large carbon capacitor, regulating the amount of carbon that resides in the atmosphere. But they are still searching for clues to understand what influences the amount of carbon in the ocean during abrupt climate changes.
Over the past two decades, ocean scientists have discovered that there are reservoirs of liquid and solid carbon dioxide accumulating at the bottom of the ocean, within the rocks and sediments on the margins of active hydrothermal vents. At these sites, volcanic magma from within the Earth meets superheated water, producing plumes of carbon dioxide-rich fluids that filter through crevices in the Earth’s crust, migrating upward towards the surface.
When a plume of this fluid meets cold seawater, the carbon dioxide can solidify into a form called hydrate. The hydrate forms a cap that traps carbon dioxide within the rocks and sediments and keeps it from entering the ocean. But at temperatures above roughly 48 degrees Fahrenheit (9 degrees Celsius), hydrate will melt, releasing buoyant liquid or gaseous carbon dioxide directly into the overlying water.
Scientists have thus far documented reservoirs of liquid and hydrate carbon dioxide in the western Pacific near Taiwan and in the Aegean Sea. In shallower waters, where ocean temperatures are warmer and pressure is lower, researchers have observed pure carbon dioxide emanating directly from sediments as a gas and rising to the ocean’s surface.
These discoveries are changing scientists’ understanding of the marine carbon system. Climate scientists have not included deep sea carbon reservoirs in current models that explore the potential impacts of future warming, because little is known about the size and distribution of these carbon sources.
In fact, there is virtually no data that documents how much carbon dioxide is currently being released from these reservoirs into the ocean. This makes the geologic history critically important: It confirms that these types of reservoirs have the capacity to release vast amounts of carbon when they are disturbed.
Analogous carbon reservoirs have also been identified in terrestrial environments. In 1979, Indonesia’s Dieng volcano suffocated 142 people when it released nearly pure carbon dioxide. In 1986, a carbon dioxide reservoir at the bottom of Lake Nyos in Cameroon erupted, killing 1,700 local villagers and hundreds of animals.
Carbon dioxide is also venting around Mammoth Mountain, California, at spots where magma rises through Earth’s crust and stalls at shallow depths. High concentrations of carbon dioxide in the soil have killed more than 100 acres of trees. Scientists are working to identify and characterize other sites on land where such releases could occur.
It is much more challenging to quantify the carbon dioxide stored in ocean reservoirs. Vast regions of the seafloor contain sites of active volcanism and hydrothermal venting, but scientists know virtually nothing about how much carbon dioxide is accumulating in surrounding rocks and sediments. In my view, there is an urgent need to study marine settings where carbon dioxide is likely accumulating, and then to assess how susceptible they may be to destabilization.
This is not an endeavor that should be deferred. Earth’s oceans are warming rapidly, and climate models project that they will warm fastest near the poles, where deep currents form that carry warming waters downward from the surface.
As these warm waters sink into the ocean’s interior, they transport excess heat towards sites where carbon dioxide reservoirs can form. Those warmer waters will eventually destabilize the hydrate seals that keep liquid carbon dioxide trapped.
One such reservoir occurs in the western Pacific west of the Okinawa Trough in the East China Sea. The temperature of the bottom waters at this location is 37 to 39 degrees Fahrenheit (3 to 4 degrees Celsius), which means the hydrate cap is within about 4-5 degrees Celsius of its melting point.
Importantly, warm hydrothermal fluids are rising from below the carbon dioxide reservoir toward the surface. As the oceans continue to warm, the temperature difference between cold ocean waters and warmer hydrothermal fluids will decrease. This will cause the hydrate to thin, potentially to a point where it will no longer keep liquid carbon dioxide from escaping.
To date there has been no research to assess whether these ocean carbon dioxide reservoirs are vulnerable to rising ocean temperatures. But Earth’s pre-historic record clearly demonstrates that geologic reservoirs can be destabilized – and that when they are, it leads to rapid increases in atmospheric carbon dioxide and global warming. In my view, this represents an important unknown risk that cannot be ignored.
9 May 2016
Humans have a long history of living on water. Our water homes span the fishing villages in Southeast Asia, Peru and Bolivia to modern floating homes in Vancouver and Amsterdam. As our cities grapple with overcrowding and undesirable living situations, the ocean remains a potential frontier for sophisticated water-based communities.
The United Nations has expressed support for further research into floating cities in response to rising sea levels and to house climate refugees. A speculative proposal, Oceanix City, was unveiled in April at the first Round Table on Sustainable Floating Cities at UN headquarters in New York.
The former tourism minister of French Polynesia, Marc Collins Chen, and architecture studio BIG advanced the proposal. Chen is involved with the Seasteading Institute, which is seeking to develop autonomous city-states floating in the shallow waters of “host nations”.
While this latest proposal has gained UN attention, it is an old idea we have repeatedly returned to over the past 70 years with little success. In fact, the Oceanix City proposal has not reached the same level of technical sophistication as previous models.
The architecture community was fascinated with marine utopias between the 1950s and ’70s. The technological optimism of this period led architects to consider whether we could build settlements in inhospitable places like the polar regions, the deserts and on the sea.
The Japanese Metabolists put forward incredible projects such as Kenzo Tange’s 1960 Tokyo Bay Plan and the marine city proposals of Kikutake and Kurokawa.
These proposals were directed at solving the impending urban crises of overpopulation and pressures on land-based resources. Many were even sophisticated enough to be patented.
The arc of this global architectural discussion was captured during the first UN Habitat conference (“Habitat I”) in Vancouver in 1976. In many ways, the UN has returned to the Vancouver Declaration from Habitat I to “[adopt] bold, meaningful and effective human settlement policies and spatial planning strategies” and to treat “human settlements as an instrument and object of development”.
We are seeing a pivoting that began in 2008 with Vincent Callebaut’s “Lilypad” - a “floating ecopolis for ecological refugees”.
Where floating cities were once dismissed as too far-fetched, the concept has been repackaged and is re-emerging into public consciousness. This time in a more politically viable state - as a means of addressing the climate emergency.
No floating settlements have ever been created on the high seas. Current offshore engineering is concerned with how cities can locate infrastructure, such as airports, nuclear power stations, bridges, oil storage facilities and stadiums, in shallow coastal environments rather than in deep international waters.
Two main types of very large floating structures (VLFS) technology can be used to carry the weight of a floating settlement.
The first, pontoon structures, are flat slabs suitable for floating in sheltered waters close to shore.
The second, semi-submersible structures (such as oil rigs), comprise platforms that are elevated on columns off the water surface. These can be located in deep waters. Potentially, oil rigs could be repurposed for such floating cities in international waters.
Oceanix City is based on the pontoon structure. This would restrict it to shallower waters with breakwaters to limit the impacts of waves. This sort of structure could serve as an extension of a coastal city, as a life raft for island communities inundated by rising waters, or to provide mobile essential services to residents of flood-prone slums.
While some early marine utopian proposals were responses to emerging urban issues, many proposals conceptualised “seaborne leisure colonies”. These communities would be independent city-states allowing inhabitants to circumvent tax laws or restrictions on medical research in their own countries.
This sort of floating city was conceived of as a micronation with sovereignty and ability to provide citizenship to its occupants. The example was set by the Principality of Sealand, off the coast of Britain.
None of these proposals have succeeded. Even modern attempts such as the Freedom Ship and the Seasteading Institute’s plans for an autonomous floating settlement under French Polynesian jurisdiction have stalled. A recent attempt at creating a sovereign micronation (seastead) off Thailand led to its proponents becoming fugitives, potentially facing the death penalty.
Technology is not a barrier to floating cities in international waters. Advances in technology enable us to create structures for habitation in deep sea waters. These schemes have never really taken off because of political and commercial barriers.
While this time round proponents are packaging floating cities in a more politically viable concept as a life raft for climate refugees, commercial barriers remain. Apart from the UN, few organisation have the economic and political influence or reason to deliver a satellite floating city in the ocean.
In my view, the future of ocean cities is in technology campuses and in tourism. Given the significant risk of a community in extreme isolation in international waters, the solution to bringing people together in mid-ocean requires us to think about what connects us: technology, work and play. In these three elements we see, perhaps, the two lowest-hanging fruits (or the most buoyant of possibilities) for ocean cities.
The first is in floating tech campuses where large technology companies set up floating data centres and campuses in international waters. Situated outside national jurisdictions, these campuses could circumvent increasingly onerous privacy regimes or offer innovative technological services without having to negotiate regulatory barriers.
The second prospect is a return to the seaborne leisure colonies of the past. Companies like Disney could expand on their cruise offerings to build floating theme parks. These resorts could be sited in international waters or hosted by coastal cities.
Given our fascination with living on water, even if Oceanix City does not suceed, it won’t be long before we see another floating city proposal. And if we get the mix of social, political and commercial drivers right, we might just find ourselves living on one.
3 June 2019
New research has revealed that marine turtle hatchlings entering the ocean close to jetties have a high likelihood of being eaten. The study, published today in Biological Conservation, found structures such as jetties are an attractive shelter for hungry fish as they lie in wait for an easy evening meal. Lead author Phillipa Wilson, a PhD candidate at The University of Western Australia (jointly supervised through the Australian Institute of Marine Science), said the study provides evidence that jetties near turtle nesting beaches increase the predation of turtle hatchlings.
“Jetties attract large numbers of predatory fish, such as mangrove jack. They provide an artificial shelter for the fish, and when located near turtle nesting beaches can greatly increase the threat to hatchlings,” she said.
“Nearly three quarters of the hatchlings entering the sea for the first time were taken by fish while still close to shore. This means that baby turtles were seven times more likely to be preyed upon than at a beach nearby with no jetty”.
Dr Scott Whiting, from the Western Australian Department of Biodiversity, Conservation and Attractions’ marine science program said this research provides evidence to assist decision making around coastal developments near turtle-nesting beaches such as jetty installation or decommissioning of infrastructure.
“As coastal development is one of the primary threats to marine turtles around the world, understanding the effects of jetties will be extremely useful to managers when advising on environmental impacts associated with these structures,” he said.
The team of scientists from UWA, AIMS, DBCA and Pendoley Environmental tracked flatback turtle hatchlings on Thevenard Island off Australia’s north west coast. This marine turtle species nests only on Australian beaches and is classified as ‘vulnerable’ by the EPBC Act.
Small, sound-emitting tags were attached to 61 recently hatched flatback turtles to monitor their movements in the ocean. Signals from the tags were detected by a grid of underwater receivers, allowing scientists to track them as they swam out to sea.
Dr Michele Thums, co-author from the Australian Institute of Marine Science, pioneered the use of the tiny tags to remotely track turtle hatchlings in water, which allowed for predation rates of hatchlings to be measured remotely for the first time.
“Only a very small proportion of turtle hatchlings survive to maturity – this may be as low as one in one thousand. As the hatchlings represent the next generation, any increase in mortality, as we document here, can effect turtle population numbers in the future,” she said.
Ms Wilson said it was normal for turtle hatchlings to swim quickly in a straight line away from the beach, out to the relative safety of the open ocean.
“However, the baby turtles we tracked behaved differently by swimming parallel to the beach and many of them resided under the jetty during the day. This is when we realised we were no longer tracking swimming hatchlings, but tagged hatchlings inside the stomach of the fish that ate them,” she said.
The predatory fish used the jetty as shelter during the day, and at night they left the jetty to feed on hatchlings along the nearshore zone.
The paper ‘High predation of marine turtle hatchlings near a coastal jetty’ was published today in Biological Conservation.
The project was a collaboration between the Australian Institute of Marine Science and The University of Western Australia with the Department of Biodiversity, Conservation and Attractions and Pendoley Environmental. Project funding was provided predominantly from DBCA through the Northwest Shelf Flatback Turtle Conservation Program.
first published by AIMS: https://www.aims.gov.au/docs/media/latest-releases
22 May 2019
One of the ocean’s top predators – the tiger shark - has been revealed as a relaxed and sometimes lazy hunter by scientists studying their behaviour. Researchers from the Australian Institute of Marine Science (AIMS) and Murdoch University’s Harry Butler Institute attached specialist tags which combined cameras with motion and environmental sensors, to 27 tiger sharks in the Ningaloo Reef off the coast of Western Australia.
Collecting 60 hours of footage, the tags revealed the 3D movements of the sharks in relation to their prey, showing a number of target species including turtles, large fish and other sharks performing escape manoeuvres when a tiger shark showed interest.
AIMS PhD graduate Dr Samantha Andrzejaczek said tiger sharks were surprisingly lazy predators.
“Our tagged sharks just continued on their courses without attempting to predate on the alert individual even if they were right in front of them,” said Dr Andrzejaczek, a lead author on a research paper released today.
“We found the sharks were more likely to use stealth to sneak up on their prey.”
AIMS senior researcher and shark expert Dr Mark Meekan said the cameras they attached to the sharks gave them an unprecedented view of the role of tiger sharks in coral reef environments. “We can begin to understand not just what the animals are eating, but how they alter the behaviours of the prey around them and how this may impact the coral reef,” Dr Meekan said. “As we come up with strategies to manage and conserve these systems into the future, we need to understand how they are controlled from the top down, meaning we need to understand how these top predators are using these reefs.”
Dr Adrian Gleiss of Murdoch University’s Harry Butler Institute compared tiger sharks to lions.
“They don’t waste energy stalking prey that are already aware of them and can easily escape,” Dr Gleiss said. “These sharks minimise energy output and chances of success by sneaking up on unsuspecting turtles and large fish.”
The tags revealed the tiger sharks frequently hunted in the shallow sandflat habitats of Ningaloo Reef.
Clamped to the dorsal fins of the sharks by hand, the tags automatically detached after 24 to 48 hours. The floating tags were tracked down using a radio antenna, and the data downloaded, providing the researchers with a day or more in the life of the shark.
The project was conducted by scientists from the Australian Institute of Marine Science, Murdoch University, the University of Western Australia and Stanford University in California.
The research paper “Biologging Tags Reveal Links Between Fine-Scale Horizontal and Vertical Movement Behaviors in Tiger Sharks” was published in Frontiers in Marine Science.
First published by AIMS (https://www.aims.gov.au/docs/media/latest-news)
1 May 2019
More than 70% of recreational fishers support no-take marine sanctuaries according to our research, published recently in Marine Policy.
This study contradicts the popular perception that fishers are against establishing no-take marine reserves to protect marine life. In fact, the vast majority of fishers we surveyed agreed that no-take sanctuaries improve marine environmental values, and do not impair their fishing.
No-take marine sanctuaries, which ban taking or disturbing any marine life, are widely recognised as vital for conservation. However, recent media coverage and policy decisions in Australia suggest recreational fishers are opposed to no-take sanctuary zones created within marine parks.
This perceived opposition has been reinforced by recreational fishing interest groups who aim to represent fishers’ opinions in policy decisions. However, it was unclear whether the opinions expressed by these groups matches those of fishers on-the-ground in established marine parks.
To answer this, we visited ten state-managed marine parks across Western Australia, South Australia, Queensland and New South Wales. We spoke to 778 fishers at boat ramps that were launching or retrieving their boats to investigate their attitudes towards no-take sanctuary zones.
Our findings debunk the myth that recreational fishers oppose marine sanctuaries. We found 72% of active recreational fishers in established marine parks (more than 10 years old) support their no-take marine sanctuaries. Only 9% were opposed, and the remainder were neutral.
We also found that support rapidly increases (and opposition rapidly decreases) after no-take marine sanctuaries are established, suggesting that once fishers have a chance to experience sanctuaries, they come to support them.
Fishers in established marine parks were also overwhelmingly positive towards marine sanctuaries. Most thought no-take marine sanctuaries benefited the marine environment (78%) and have no negative impacts on their fishing (73%).
We argue that recreational fishers, much like other Australians, support no-take marine sanctuaries because of the perceived environmental benefits they provide. This is perhaps not surprising, considering that appreciating nature is one of the primary reasons many people go fishing in the first place.
In the past opposition from recreational fishing groups has been cited in the decision to scrap proposed no-take sanctuaries around Sydney, to open up established no-take sanctuaries to fishing and to reduce sanctuaries within the Australia Marine Parks (formerly the Commonwealth Marine Reserve network).
Our findings suggest that these policy decisions do not reflect the beliefs of the wider recreational fishing community, but instead represent the loud voices of a minority.
We suggest that recreational fishing groups and policy makers should survey grass roots recreational fishing communities (and other people who use marine parks) to gauge the true level of support for no-take marine sanctuaries, before any decisions are made.
Despite what headlines may say, no-take marine sanctuaries are unlikely to face long lasting opposition from recreational fishers. Instead, our research suggests no-take marine sanctuaries provide a win-win: protecting marine life whilst fostering long term support within the recreational fishing community.
Matt Navarro, Post-doctoral Fellow, University of Western Australia; Marit E. Kragt, Senior Lecture in Agricultural and Resource Economics, and Tim Langlois, Research Fellow, University of Western Australia
Feb 18 2019
Much of the Great Barrier Reef is legally protected in an effort to conserve and rebuild the fragile marine environment. Marine reserves are considered the gold standard for conservation, and often shape our perception of what an “undisturbed ecosystem” should look like.
However our research, published today in Frontiers in Ecology and the Environment, suggests that “no-take” marine reserves may be failing shark populations on the Great Barrier Reef.
After 40 years of protection, the average amount of reef sharks in no-take reserves (areas where fishing is forbidden but people can boat or swim) was only one-third that in strictly enforced human exclusion areas. The difference, we argue, is down to poaching, raising serious questions about the effectiveness of no-take reserves.
Three species of shark are dominant on Indo-Pacific coral reefs: grey reef sharks, blacktip reef sharks, and whitetip reef sharks. All three of these species are considered high-level predators, but the combination of slow reproductive rates and high fishing pressure has depleted reef shark populations across much of their range.
Well-designed and enforced no-take marine reserves help rebuild reef shark populations, but it is not known whether these reserves can facilitate full recovery to baseline (unexploited) levels, or how long the recovery process might take.
No-take marine reserves are firmly advocated as an effective way to combat overfishing. With few exceptions, well-enforced no-take marine reserves result in rapid increases in target fish populations, leading to flow-on benefits such as better fisheries in outlying areas.
In many cases, no-take marine reserves are considered to have intact ecology and therefore drive our perceptions of what undisturbed ecosystems should look like.
The entire Great Barrier Reef was open to fishing until 1980, when no-take reserves were established. More reserves were created over the next two and a half decades, resulting in reserves that vary in age from 14-39 years. A small number of no-entry reserves, which are completely off limits to humans, were also implemented during this period to guard against the potential effects of activities such as boating and diving.
Given that fishing is prohibited in both no-take and no-entry reserves, we expected shark populations to be similar in both areas. Due to the exclusion of humans from no-entry reserves, shark populations within these areas are largely unknown and have only been assessed once, 10 years after protection.
Read more: Killing sharks is killing coral reefs too
This past research revealed that shark populations were much greater inside no-entry reserves compared to no-take reserves, but this does not allow us to determine whether recovery is ongoing or complete. The diverse ages of marine reserves within the GBR provide a unique opportunity to investigate the potential recovery of reef shark populations and evaluate the performance of no-entry and no-take reserves as tools for shark conservation.
Using underwater survey data from 11 no-take reserves and 13 no-entry reserves, we reconstructed reef shark populations through the past four decades of protection. Surprisingly, we found shark populations were substantially higher – with two-thirds more biomass – in no-entry reserves than in no-take reserves, indicating that the latter do not support near-natural shark populations.
We looked at potential drivers of shark abundance and found that coral cover, habitat complexity, reef size, distance to shore, and the distance to the nearest fished reef could not explain the large differences between no-take and no-entry reserves.
We argue the disparity between no-entry and no-take reserves is likely due to poaching in no-take reserves. Recent research found up to 18% of recreational fishers admit to fishing illegally.
Enforcement of no-entry reserves is much easier than no-take reserves as evidence of fishing is not required for prosecution. On the other hand, vessels are allowed to be present in no-take reserves, leaving these areas susceptible to poaching. Given the slow reproductive rate of reef sharks, even small amounts of fishing may reduce their populations.
The Great Barrier Reef is one of the most intensely managed marine parks in the world. Despite this, our results reveal that no-take reserves fall well short of restoring shark populations to near-natural levels, and that up to 40 years of strong protection is required to rebuild shark populations.
These results also highlight that no-take marine reserves inadequately reflect ecological baselines and that we may need to reevaluate what we consider to be a natural, intact reef ecosystem.
While the creation of more and larger no-entry reserves may solve the problem, this approach is likely to be unpopular and politically undesirable. An alternative approach, would be to tackle poaching by enlisting fishing communities in the fight against illegal fishing, better education, and increasing enforcement.
February 1 2019
The devastating bleaching on the Great Barrier Reef in 2016 and 2017 rightly captured the world’s attention. But what’s less widely known is that another World Heritage-listed marine ecosystem in Australia, Shark Bay, was also recently devastated by extreme temperatures, when a brutal marine heatwave struck off Western Australia in 2011.
A 2018 workshop convened by the Shark Bay World Heritage Advisory Committee classified Shark Bay as being in the highest category of vulnerability to future climate change. And yet relatively little media attention and research funding has been paid to this World Heritage Site that is on the precipice.
Shark Bay, in WA’s Gascoyne region, is one of 49 marine World Heritage Sites globally, but one of only four of these sites that meets all four natural criteria for World Heritage listing. The marine ecosystem supports the local economy through tourism and fisheries benefits.
Around 100,000 tourists visit Shark Bay each year to interact with turtles, dugongs and dolphins, or to visit the world’s most extensive population of stromatolites – stump-shaped colonies of microbes that date back billions of years, almost to the dawn of life on Earth.
Commercial and recreational fishing is also extremely important for the local economy. The combined Shark Bay invertebrate fishery (crabs, prawns and scallops) is the second most valuable commercial fishery in Western Australia.
However, this iconic and valuable marine ecosystem is under serious threat. Shark Bay is especially vulnerable to future climate change, given that the temperate seagrass that underpins the entire ecosystem is already living at the upper edge of its tolerable temperature range. These seagrasses provide vital habitat for fish and marine mammals, and help the stromatolites survive by regulating the water salinity.
Shark Bay received the highest rating of vulnerability using the recently developed Climate Change Vulnerability Index, created to provide a method for assessing climate change impacts across all World Heritage Sites.
In particular, extreme marine heat events were classified as very likely and predicted to have catastrophic consequences in Shark Bay. By contrast, the capacity to adapt to marine heat events was rated very low, showing the challenges Shark Bay faces in the coming decades.
The region is also threatened by increasingly frequent and intense storms, and warming air temperatures.
To understand the potential impacts of climatic change on Shark Bay, we can look back to the effects of the most recent marine heatwave in the area. In 2011 Shark Bay was hit by a catastrophic marine heatwave that destroyed 900 square kilometres of seagrass – 36% of the total coverage.
This in turn harmed endangered species such as turtles, contributed to the temporary closure of the commercial crab and scallop fisheries, and released between 2 million and 9 million tonnes of carbon dioxide – equivalent to the annual emissions from 800,000 homes.
Some aspects of Shark Bay’s ecosystem have never been the same since. Many areas previously covered with large, temperate seagrasses are now bare, or have been colonised by small, tropical seagrasses, which do not provide the same habitat for animals. This mirrors the transition seen on bleached coral reefs, which are taken over by turf algae. We may be witnessing the beginning of Shark Bay’s transition from a sub-tropical to a tropical marine ecosystem.
This shift would jeopardise Shark Bay’s World Heritage values. Although stromatolites have survived for almost the entire history of life on Earth, they are still vulnerable to rapid environmental change. Monitoring changes in the microbial makeup of these communities could even serve as a canary in the coalmine for global ecosystem changes.
Despite Shark Bay’s significance, and the seriousness of the threats it faces, it has received less media and funding attention than many other high-profile Australian ecosystems. Since 2011, the Australian Research Council has funded 115 research projects on the Great Barrier Reef, and just nine for Shark Bay.
The World Heritage Committee has recognised that local efforts alone are no longer enough to save coral reefs, but this logic can be extended to other vulnerable marine ecosystems – including the World Heritage values of Shark Bay.
Safeguarding Shark Bay from climate change requires a coordinated research and management effort from government, local industry, academic institutions, not-for-profits and local Indigenous groups – before any irreversible ecosystem tipping points are reached. The need for such a strategic effort was obvious as long ago as the 2011 heatwave, but it hasn’t happened yet.
Due to the significant Aboriginal heritage in Shark Bay, including three language groups (Malgana, Nhanda and Yingkarta), it will be vital to incorporate Indigenous knowledge, so as to understand the potential social impacts.
And of course, any on-the-ground actions to protect Shark Bay need to be accompanied by dramatic reductions in greenhouse emissions. Without this, Shark Bay will be one of the many marine ecosystems to fundamentally change within our lifetimes.
Matthew Fraser, Postdoctoral Research Fellow, University of Western Australia; Ana Sequeira, ARC DECRA Fellow, University of Western Australia; Brendan Paul Burns, Senior Lecturer, UNSW; Diana Walker, Emeritus Professor, University of Western Australia; Jon C. Day, PSM, Post-career PhD candidate, ARC Centre of Excellence for Coral Reef Studies, James Cook University, and Scott Heron, Senior Lecturer, James Cook University
February 8 2019
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.
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.
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.
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.
14 December 2018
The Antarctic Circumpolar Current, or ACC, is the strongest ocean current on our planet. It extends from the sea surface to the bottom of the ocean, and encircles Antarctica.
It is vital for Earth’s health because it keeps Antarctica cool and frozen. It is also changing as the world’s climate warms. Scientists like us are studying the current to find out how it might affect the future of Antarctica’s ice sheets, and the world’s sea levels.
The ACC carries an estimated 165 million to 182 million cubic metres of water every second (a unit also called a “Sverdrup”) from west to east, more than 100 times the flow of all the rivers on Earth. It provides the main connection between the Indian, Pacific and Atlantic Oceans.
The tightest geographical constriction through which the current flows is Drake Passage, where only 800 km separates South America from Antarctica. While elsewhere the ACC appears to have a broad domain, it must also navigate steep undersea mountains that constrain its path and steer it north and south across the Southern Ocean.
A satellite view over Antarctica reveals a frozen continent surrounded by icy waters. Moving northward, away from Antarctica, the water temperatures rise slowly at first and then rapidly across a sharp gradient. It is the ACC that maintains this boundary.
The ACC is created by the combined effects of strong westerly winds across the Southern Ocean, and the big change in surface temperatures between the Equator and the poles.
Ocean density increases as water gets colder and as it gets more salty. The warm, salty surface waters of the subtropics are much lighter than the cold, fresher waters close to Antarctica. We can imagine that the depth of constant density levels slopes up towards Antarctica.
The westerly winds make this slope steeper, and the ACC rides eastward along it, faster where the slope is steeper, and weaker where it’s flatter.
In the ACC there are sharp changes in water density known as fronts. The Subantarctic Front to the north and Polar Front further south are the two main fronts of the ACC (the black lines in the images). Both are known to split into two or three branches in some parts of the Southern Ocean, and merge together in other parts.
Scientists can figure out the density and speed of the current by measuring the ocean’s height, using altimeters. For instance, denser waters sit lower and lighter waters stand taller, and differences between the height of the sea surface give the speed of the current.
The path of the ACC is a meandering one, because of the steering effect of the sea floor, and also because of instabilities in the current.
The ACC also plays a part in the meridional (or global) overturning circulation, which brings deep waters formed in the North Atlantic southward into the Southern Ocean. Once there it becomes known as Circumpolar Deep Water, and is carried around Antarctica by the ACC. It slowly rises toward the surface south of the Polar Front.
Once it surfaces, some of the water flows northward again and sinks north of the Subarctic Front. The remaining part flows toward Antarctica where it is transformed into the densest water in the ocean, sinking to the sea floor and flowing northward in the abyss as Antarctic Bottom Water. These pathways are the main way that the oceans absorb heat and carbon dioxide and sequester it in the deep ocean.
The ACC is not immune to climate change. The Southern Ocean has warmed and freshened in the upper 2,000 m. Rapid warming and freshening has also been found in the Antarctic Bottom Water, the deepest layer of the ocean.
Waters south of the Polar Front are becoming fresher due to increased rainfall there, and waters to the north of the Polar Front are becoming saltier due to increased evaporation. These changes are caused by human activity, primarily through adding greenhouse gases to the atmosphere, and depletion of the ozone layer. The ozone hole is now recovering but greenhouse gases continue to rise globally.
Winds have strengthened by about 40% over the Southern Ocean over the past 40 years. Surprisingly, this has not translated into an increase in the strength of the ACC. Instead there has been an increase in eddies that move heat towards the pole, particularly in hotspots such as Drake Passage, Kerguelen Plateau, and between Tasmania and New Zealand.
We have observed much change already. The question now is how this increased transfer of heat across the ACC will impact the stability of the Antarctic ice sheet, and consequently the rate of global sea-level rise.
Helen Phillips, Senior Research Fellow, Institute for Marine and Antarctic Studies, University of Tasmania; Benoit Legresy, , CSIRO, and Nathan Bindoff, Professor of Physical Oceanography, Institute for Marine and Antarctic Studies, University of Tasmania
The lost world was uncovered during detailed seafloor mapping by CSIRO research vessel Investigator while on a 25-day research voyage led by scientists from the Australian National University (ANU). The mapping has revealed, for the first time, a diverse chain of volcanic seamounts located in deep water about 400 km east of Tasmania. The seamounts tower up to 3000 m from the surrounding seafloor but the highest peaks are still far beneath the waves, at nearly 2000 m below the surface. Dr Tara Martin, from the CSIRO mapping team, said the mapping offered a window into a previously unseen and spectacular underwater world.
“Our multibeam mapping has revealed in vibrant detail, for the first time, a chain of volcanic seamounts rising up from an abyssal plain about 5000m deep, Dr Martin said. "The seamounts vary in size and shape, with some having sharp peaks while others have wide flat plateaus, dotted with small conical hills that would have been formed by ancient volcanic activity. “Having detailed maps of such areas is important to help us better manage and protect these unique marine environments, and provides a stepping stone for future research.
“This is a very diverse landscape and will undoubtedly be a biological hotspot that supports a dazzling array of marine life,” she said. Ship data collected during the voyage revealed spikes in ocean productivity over the chain of seamounts, with increased phytoplankton activity and marine animal observations in the area.
Dr Eric Woehler from BirdLife Tasmania, who was on Investigator with a team conducting seabird and marine mammal surveys, was astounded by the amount of life they saw above the seamounts.
“While we were over the chain of seamounts, the ship was visited by large numbers of humpback and long-finned pilot whales,” Dr Woehler said. “We estimated that at least 28 individual humpback whales visited us on one day, followed by a pod of 60-80 long-finned pilot whales the next. We also saw large numbers of seabirds in the area including four species of albatross and four species of petrel.”
“Clearly, these seamounts are a biological hotspot that supports life, both directly on them, as well as in the ocean above,” he said.
Research indicates that seamounts may be vital stopping points for some migratory animals, especially whales. Whales may use these seafloor features as navigational aids during their migration. “These seamounts may act as an important signpost on an underwater migratory highway for the humpback whales we saw moving from their winter breeding to summer feeding grounds,” Dr Woehler said. “Lucky for us and our research, we parked right on top of this highway of marine life!” The life and origin of the seamounts will be further studied later this year when Investigator returns to the region for two further research voyages departing in November and December. A range of surveys will be conducted on these voyages, including capturing high resolution video of marine life on the seamounts using deep water cameras, and collecting rock samples to better understand their formation and origin. Dr Woehler will be on the first of these voyages and expects further surprises on the return visit. “We expect that these seamounts will be a biological hotspot year round, and the summer visit will give us another opportunity to uncover the mysteries of the marine life they support,” said Dr Woehler.
Research vessel Investigator is Australia’s only research vessel dedicated to blue-water research, and is owned and operated by CSIRO – Australia’s national science agency. The vessel conducts research year round, and is made available to Australian researchers and their international collaborators.
11 October 2018, First published by CSIRO, at: https://www.csiro.au/en/News/News-releases/2018/Scientists-uncover-volcanic-lost-world
Four tiger sharks have now been captured and killed following two separate attacks off the coast of North Queensland last week. Despite being relatively rare, shark attacks – or the threat of attacks – not only disrupt recreational beach activities, but can affect associated tourist industries.
Shark nets are a common solution to preventing shark attacks on Australian beaches, but they pose dangers to marine ecosystems.
Seeking a cost-effective way to monitor beach safety over large areas, we have developed a system called SharkSpotter. It combines artificial intelligence (AI), computing power, and drone technology to identify and alert lifesavers to sharks near swimmers.
SharkSpotter was named the national AI or Machine Learning Innovation of the Year at the Australian Information industry Association (AIIA) annual iAwards this month.
The project is a collaboration between the University of Technology Sydney and The Ripper Group, which is pioneering the use of drones – called “Westpac Little Ripper Lifesavers” – in the search and rescue movement in Australia.
SharkSpotter can detect sharks and other potential threats using real-time aerial imagery. The system analyses streaming video from a camera attached to a drone (an unmanned aerial vehicle, or UAV) to monitor beaches for sharks, issue alerts, and conduct rescues.
Developed using machine learning techniques known as “deep learning”, the SharkSpotter system receives streaming imagery from the drone camera and attempts to identify all objects in the scene. Once valid objects are detected, they are put into one of 16 categories: shark, whale, dolphin, rays, different types of boats, surfers, and swimmers.
If a shark is detected, SharkSpotter provides both a visual indication on the computer screen and an audible alert to the operator. The operator verifies the alert and sends text messages from the SharkSpotter system to the Surf Life Savers for further action.
In an emergency, the drone is equipped with a lifesaving flotation pod together with an electronic shark repellent that can be dropped into the water in cases where swimmers are in severe distress, trapped in a rip, or if there are sharks close by.
The development of SharkSpotter involved several stages.
Among the most time-consuming tasks was collecting and annotating the necessary data. The data were collected by The Ripper Group by flying a drone with a camera attached to it above different Australian beaches.
We then manually annotated each video to indicate the specific location of sharks and other objects. The video frames and the annotations were then used to train the deep learning algorithm to correctly identify and classify objects.
These advanced machine learning techniques significantly improve aerial detection to more than 90% accuracy. That’s much better than conventional techniques such as helicopters with human spotters (17.1%) and fixed-wing aircraft spotters (12.5%).
We tested the system at different Australian beaches to determine the varying parameters, such as camera resolution, height above sea level (which can affect the vision clarity of drones), speed and flight duration.
After successful trials and fine-tuning of the system, SharkSpotter was used across a dozen popular beaches in New South Wales and Queensland last summer.
The system was developed to help Surf Life Savers monitor the beach more effectively – as opposed to replacing them – and has been received positively by end-users and communities alike, according to a survey conducted by The Ripper Group.
In January 2018, the Westpac Little Ripper Lifesaver was used to rescue two young swimmers caught in a rip at Lennox Head, NSW.
The drone flew down the beach some 800 metres from the lifeguard station, and a lifesaving flotation pod was dropped from the drone. The complete rescue operation took 70 seconds.
We believe SharkSpotter is a win-win for both marine life and beachgoers. From a technology perspective, it has demonstrated how to detect moving objects in a complex, dynamic marine environment from a fast-moving drone.
This unique technology combines dynamic video image processing AI and advanced drone technology to creatively address the global challenge of ensuring safe beaches, protecting marine environments, and enhancing tourism.
The authors would like to acknowledge the contributions of Dr Paul Scully Power, co-founder of The Ripper Group, who partnered in the development of SharkSpotter.
Nabin Sharma, Senior Lecturer, UTS School of Software, University of Technology Sydney and Michael Blumenstein, Associate Dean Research (Strategy and Management) at the University of Technology Sydney, University of Technology Sydney
This article is republished from The Conversation under a Creative Commons license.
28 September 2018
It’s stunning but true that we know more about the surface of the moon than about the Earth’s ocean floor. Much of what we do know has come from scientific ocean drilling – the systematic collection of core samples from the deep seabed. This revolutionary process began 50 years ago, when the drilling vessel Glomar Challenger sailed into the Gulf of Mexico on August 11, 1968 on the first expedition of the federally funded Deep Sea Drilling Project.
I went on my first scientific ocean drilling expedition in 1980, and since then have participated in six more expeditions to locations including the far North Atlantic and Antaractica’s Weddell Sea. In my lab, my students and I work with core samples from these expeditions. Each of these cores, which are cylinders 31 feet long and 3 inches wide, is like a book whose information is waiting to be translated into words. Holding a newly opened core, filled with rocks and sediment from the Earth’s ocean floor, is like opening a rare treasure chest that records the passage of time in Earth’s history.
Over a half-century, scientific ocean drilling has proved the theory of plate tectonics, created the field of paleoceanography and redefined how we view life on Earth by revealing an enormous variety and volume of life in the deep marine biosphere. And much more remains to be learned.
Two key innovations made it possible for research ships to take core samples from precise locations in the deep oceans. The first, known as dynamic positioning, enables a 471-foot ship to stay fixed in place while drilling and recovering cores, one on top of the next, often in over 12,000 feet of water.
Anchoring isn’t feasible at these depths. Instead, technicians drop a torpedo-shaped instrument called a transponder over the side. A device called a transducer, mounted on the ship’s hull, sends an acoustic signal to the transponder, which replies. Computers on board calculate the distance and angle of this communication. Thrusters on the ship’s hull maneuver the vessel to stay in exactly the same location, countering the forces of currents, wind and waves.
Another challenge arises when drill bits have to be replaced mid-operation. The ocean’s crust is composed of igneous rock that wears bits down long before the desired depth is reached.
When this happens, the drill crew brings the entire drill pipe to the surface, mounts a new drill bit and returns to the same hole. This requires guiding the pipe into a funnel shaped re-entry cone, less than 15 feet wide, placed in the bottom of the ocean at the mouth of the drilling hole. The process, which was first accomplished in 1970, is like lowering a long strand of spaghetti into a quarter-inch-wide funnel at the deep end of an Olympic swimming pool.
When scientific ocean drilling began in 1968, the theory of plate tectonics was a subject of active debate. One key idea was that new ocean crust was created at ridges in the seafloor, where oceanic plates moved away from each other and magma from earth’s interior welled up between them. According to this theory, crust should be new material at the crest of ocean ridges, and its age should increase with distance from the crest.
The only way to prove this was by analyzing sediment and rock cores. In the winter of 1968-1969, the Glomar Challenger drilled seven sites in the South Atlantic Ocean to the east and west of the Mid-Atlantic ridge. Both the igneous rocks of the ocean floor and overlying sediments aged in perfect agreement with the predictions, confirming that ocean crust was forming at the ridges and plate tectonics was correct.
The ocean record of Earth’s history is more continuous than geologic formations on land, where erosion and redeposition by wind, water and ice can disrupt the record. In most ocean locations sediment is laid down particle by particle, microfossil by microfossil, and remains in place, eventually succumbing to pressure and turning into rock.
Microfossils (plankton) preserved in sediment are beautiful and informative, even though some are smaller than the width of a human hair. Like larger plant and animal fossils, scientists can use these delicate structures of calcium and silicon to reconstruct past environments.
Thanks to scientific ocean drilling, we know that after an asteroid strike killed all non-avian dinosaurs 66 million years ago, new life colonized the crater rim within years, and within 30,000 years a full ecosystem was thriving. A few deep ocean organisms lived right through the meteorite impact.
Ocean drilling has also shown that ten million years later, a massive discharge of carbon – probably from extensive volcanic activity and methane released from melting methane hydrates – caused an abrupt, intense warming event, or hyperthermal, called the Paleocene-Eocene Thermal Maximum. During this episode, even the Arctic reached over 73 degrees Fahrenheit.
The resulting acidification of the ocean from the release of carbon into the atmosphere and ocean caused massive dissolution and change in the deep ocean ecosystem.
This episode is an impressive example of the impact of rapid climate warming. The total amount of carbon released during the PETM is estimated to be about equal to the amount that humans will release if we burn all of Earth’s fossil fuel reserves. Yet, an important difference is that the carbon released by the volcanoes and hydrates was at a much slower rate than we are currently releasing fossil fuel. Thus we can expect even more dramatic climate and ecosystem changes unless we stop emitting carbon.
Scientific ocean drilling has also shown that there are roughly as many cells in marine sediment as in the ocean or in soil. Expeditions have found life in sediments at depths over 8000 feet; in seabed deposits that are 86 million years old; and at temperatures above 140 degrees Fahrenheit.
Today scientists from 23 nations are proposing and conducting research through the International Ocean Discovery Program, which uses scientific ocean drilling to recover data from seafloor sediments and rocks and to monitor environments under the ocean floor. Coring is producing new information about plate tectonics, such as the complexities of ocean crust formation, and the diversity of life in the deep oceans.
This research is expensive, and technologically and intellectually intense. But only by exploring the deep sea can we recover the treasures it holds and better understand its beauty and complexity.
This article is republished from The Conversation under a Creative Commons license.
26 September 2018
Researchers at the Australian Institute of Marine Science have made a significant breakthrough in the war against crown-of-thorns starfish, on the Great Barrier Reef.
AIMS’ senior research leader Dr Sven Uthicke and biochemist Jason Doyle, along with echinoderm expert Dr Miles Lamare from the University of Otago, in New Zealand, have developed a cost effective method for detecting DNA of the coral-eating pest.
Dr Uthicke said the method would improve monitoring and early detection of the reef pest, also known as crown-of-thorns seastar, allowing reef managers to contain outbreaks sooner.
“It’s a genetic probe which we had developed to detect seastar larvae in plankton and we have been able to modify the method,” Dr Uthicke said. “We have worked on this for the past three years, and we have been able to adapt this to make it more sensitive to detect adult crown-of-thorns seastar.” Ecological monitoring has so far failed to detect early stages of an outbreak which has prevented timely intervention.
Dr Uthicke said the current method for detecting outbreaks were on-reef field surveys using divers but by the time these methods detect outbreaks, the outbreak is usually well established. “Standard monitoring techniques only identify about 5 per cent of the pest on reefs, but this new method will allow us to clearly identify whether greater numbers are present,” Dr Uthicke said. “It counts the number of gene copies in the sample of seawater from a reef using a novel technique called digital droplet PCR.”
During recent field work, using the probe on 11 reefs of the Great Barrier Reef, crown-of-thorns starfish DNA was detectable on those suffering outbreaks. In contrast, crown-of-thorns starfish DNA was absent from ‘post-outbreak’ reefs after populations collapsed, and from ‘pre-outbreak’ reefs.
The fourth wave of outbreaks since the 1960s started around 2010 on Australia’s far northern Great Barrier Reef and has seen the significant loss of coral cover to the voracious appetite of the starfish, making it a major contributor to the coral reef crisis. This outbreak has spread as far south as Townsville along the Great Barrier Reefs, and is expected to continue south. This research project was partly funded by The National Environmental Science Program (NESP), the Great Barrier Reef Marine Park Authority and philanthropist Ian Potter Foundation.
The paper ‘eDNA detection of corallivorous seastar (Acanthaster cf. solaris) outbreaks on the Great Barrier Reef using digital droplet PCR’ is available online in the journal Coral Reefs.
18 September 2018, Australian Institute of Marine Science, 2018
The whale shark is the largest fish in the world, but much of its lifecycle remains shrouded in mystery. These gentle giants gather in just a handful of places around the globe – something which has long baffled scientists – but our new research has started to explain why. Better understanding of whale shark movements could help prevent further population loss in a species that has already experienced a 63% population decline over the past 75 years.
When swimming solo, the whale shark, which can grow up to 18.8 metres in length and 34 tons in weight, travels all over the world. Recently, a group of scientists tracked the remarkable journey of one whale shark across the Pacific from Panama to the Philippines. At more than 12,000 miles it proved to be one of the longest migrations ever recorded.
Yet whale sharks are known to come together at just a few specific locations around the world. Anything from ten to 500 whale sharks may gather at any one time in areas off the coasts of Australia, Belize, the Maldives, Mexico and more.
Approximately 20 hotspots have been identified – mere pinpricks in the vastness of the world’s oceans – but we don’t know what exactly attracts the whale sharks to them. In some cases the sites are linked to a specific biological phenomenon – such as the spawning of land crabs at Christmas Island in the Indian Ocean, which provides whale sharks with the seasonal equivalent of a Christmas feast. Our new research aimed to discover whether there was something else that united the places where these giants of the ocean hang out.
The physical features of these spots – known as their bathymetry – have been shown to influence gathering points in other marine species. So in collaboration with the Maldives Whale Shark Research Programme, we decided to investigate whether it drives whale shark gatherings in the same way.
Our new global study shows that whale sharks congregate in specific areas of shallow water, next to steep slopes that quickly give way to areas much deeper water (usually between 200 metres and 1,000 metres).
We identified three main reasons. First, the deep water is used by whale sharks for feeding. Studies have shown the sharks diving to depths of almost 2 kilometres (1,928 metres to be precise) to feed on zooplankton and squid.
Second, the steep slopes are known to bring nutrients up to the surface from the deep, which in turn increases the abundance of plankton and attracts large numbers of filter feeding species. And finally, in shallow water, as well as feeding on coral and fish spawn, the sharks are able to thermoregulate, warming themselves back up after their dives into deep water which gets as cold as 4℃.
If you’ve ever seen or swum with a whale shark, it was most likely in one of these relatively shallow aggregation areas. Knowing where these hotspots are has provided local communities with a windfall from ecotourism. In the Maldives alone, economic benefits from whale shark-related activities were estimated at US$9.4m per year. Whale sharks are worth a lot more alive than dead – and with many of these meeting points in developing countries, the income is invaluable.
But with the increasing pressures of tourism comes new dangers for the sharks. Crowds of snorkelers and tourist vessels are increasingly disturbing the whale shark’s waters, and – more worryingly – risk potentially fatal strikes by boats. To protect these beautiful creatures and continue to reap the rewards of ecotourism, we recommend that marine protected areas should be set up around whale shark gatherings and codes of practice be followed when interacting with them.
These discoveries have narrowed down some of the key reasons why whale sharks congregate where they do, but many mysteries remain. Do individuals travel between these hotspots? Coastal gatherings are predominately made up of immature male sharks, usually still just four or five metres long. So where are all the girls? And where do whale sharks mate and give birth? Mating and pupping have never been seen in the wild – but, intriguingly, up to 90% of the whale sharks passing through the Galapagos marine reserve are female and thought to be pregnant.
Could this be a key labour ward for the world’s whale sharks? Last year a BBC film crew at the Galapagos attempted to follow a pregnant female in a submersible to watch it give birth, but to no avail. That’s one secret that the depths are keeping for now.
7 July 2018
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.
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:
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.
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.
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).
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.
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.
It’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.
27 February 2018
After several sightings of protected Humpback whales migrating along the east coast over the past two weeks, NSW Department of Primary Industries Minister Niall Blair has announced the second NSW North Coast net trial will come to an end.
NSW is also removing shark nets from their other 51 sites for the whale migration season. Whilst NSW is removing gear to prevent whale entanglements, Queensland continues at the peril of these majestic marine mammals. Please sign these petitions to demonstrate your support for marine animals.
Sea Shepherd welcomes the NSW Government announcement that ended the northern NSW shark net trial which was putting these ocean giants at too great a risk. Whale tourism is an important industry in Queensland with some of the finest whale watching tours available in centres from the Gold Coast to Hervey Bay and to Cairns and Port Douglas. Locals and tourists want to see these animals swimming freely without the risk of entanglement.
Sea Shepherd's Operation Apex Harmony team saw possibly 11 entanglements in Queensland Shark Control Program gear last year with a whale calf killed at Kurrawa in a shark net. Fellow campaigner and marine scientist, CEO of Humpbacks and Highrises, Dr Olaf Meynecke said: “Our organisation has long campaigned for the replacement of the shark nets in the Gold Coast as they are a major risk to protected marine life including whales who use the bay as a resting and calving ground each year.
"NSW has removed shark nets whilst only a few kilometres across the border in the Gold Coast bay whale entanglements will continue. More than 1/3 of recorded Humpback whale incidents along the Queensland coastline are in fact due to the Queensland Shark Control Program and we urgently need to change the current practice in light of an increasing whale population. "Alternative methods are available that do not put the life of humans or whales in danger.” Sea Shepherd Australia's Managing Director Mr Hansen also stated: “Sea Shepherd is concerned for human safety. It is not a question of protecting human safety at cost to the marine environment. You can have both human safety and marine animal protection with the many non-lethal alternatives to nets and drum lines available right now.”
Originally published at: http://www.seashepherd.org.au/news-and-commentary/news/sea-shepherd-calls-for-shark-net-removal-in-queensland.html
4 May 2018
Given white sharks get the (sea)lion’s share of media attention, you may be surprised to learn that we don’t know a whole lot about them. Sure, we know some pretty cool stuff already: they give birth to live young, can swim over 60km an hour and are an apex predator. But because they swim huge distances and are lone travellers it’s hard to get to know them really well. Scientists love a challenge though, so, courtesy of their tireless efforts to study these great creatures, here are four facts you probably didn’t know.
Tagging data and genetic evidence suggests two populations of white sharks Carchardon carcharias (commonly known as the great white shark) exist in Australia: an eastern population ranging from Tasmania to central Queensland and across to New Zealand, and a southern-western population ranging from western Victoria to north-western Western Australia.
There’s a popular saying in the marine world: ‘counting fish is like counting trees, but you can’t see them and they move around all the time.’ Sounds impossible, right? Not for our scientists: in a world first we’ve used a unique combination of electronic tagging and tracking, collection of tissue samples, and a combined genetic and statistical technique called ‘close-kin mark recapture’ to estimate the Australian white shark populations. ‘Close-kin mark recapture’ means we compared the genetic data from juvenile white sharks to figure out how many shared a mother or father. This number can reveal the overall number of breeding adults: a smaller adult population means lots of half and full brothers and sisters, and vice versa. Through the juvenile’s DNA, we’re learning a whole lot about the adult population without having to track them down.
The only catch – you need to know where the cool kids hang (the nursery areas for juvenile white sharks) so you can tag them and collect samples. The eastern juveniles have a few choice locations but their southern-western counterparts are keeping tight-lipped about their favourite spots, meaning we couldn’t conduct the same study with them. Despite this, we were able to estimate the southern-western adult population size to be 1460 (with a range of between 760 and 2250).
But what of the eastern population? We estimate the total population to be 5,460 (with a range of between 2909 and 12,802). We’re not sure if this is historically high, low or somewhere in-between because we have nothing to compare it with, but at least we now have a starting point.
White sharks take a relatively long time to reach maturity — 12 to 15 years — which means they’re slow to reproduce. These are the badges of evolutionary honour a species gets to wear for being extremely successful. However, these same traits mean that if the number of mature white sharks dropped suddenly, the entire species could be under threat. Until now, we had no idea how many juvenile sharks survive to maturity, an important piece of the population puzzle. Another incredible thing our researchers have uncovered is the mortality rate of juvenile sharks in the eastern population. Using data from around 70 juvenile sharks fitted with an acoustic emitter we estimated that juvenile sharks had an annual survival rate of around 73 per cent.
While it’s true the overall number of shark attacks has gradually increased in the past few decades in Australia, many different factors unrelated to shark numbers contribute to the overall increase in shark attacks. These include human population trends, changes in human population distribution and regional demographics, as well as variations in lifestyle and behaviour of people over time. However, clusters of shark attacks cannot be attributed to increases in human use of the ocean, or sudden increases in overall shark population size, because neither of these change over such short periods.
There are, for example, high human-use areas where white sharks are abundant but the incidence of shark attack is low. The drumline program in Western Australia revealed a significant number of tiger sharks present in coastal waters off Perth, yet no attacks have been attributed to this species in the area since 1925 according to the Australian Shark Attack file. Incidence and frequency of shark attacks may not relate directly to local shark abundance and cannot be used as a proxy for shark population trend.
So, what does all this new information mean? Now that we have a starting point for shark populations, we’ll be repeating the process over time to build population trends – a crucial step for developing effective policy outcomes for conservation and risk management.
Original article published https://blog.csiro.au/4-things-didnt-know-white-sharks/
9 February 2018
Scientists from James Cook University (JCU) and the Australian Institute of Marine Science (AIMS) have developed a new method to study microplastics swallowed by sea turtles.
The new technique will help assess whether microplastics are as dangerous to turtles as larger pieces of plastic.
Recent estimates suggest there are more than 5 trillion pieces of plastic debris floating in the world's oceans, a figure which doesn’t include waste on beaches or the seafloor.
JCU’s Associate Professor Ellen Ariel said contamination of marine life by microplastics – pieces of plastic smaller than 5 mm in length - is poorly known and likely to be under-reported.
AIMS@JCU student Alexandra Caron, led the study. “As with bigger pieces of plastic, once swallowed, ingested microplastics may impact organisms physically as well as physiologically as they can leach associated plastic chemicals or other absorbed pollutants into the animal causing toxicity,” she said.
Sea turtles are at particular risk from plastics in the oceans because the seven species of marine turtles are already categorised as vulnerable to critically endangered.“They look for things like jellyfish to eat, and a piece of soft floating plastic can appear very similar. Plastic debris can also become entangled among green turtle food sources such as seagrass leaves and seaweed. Turtles don’t have the capacity to regurgitate, so plastic particles tend to be swallowed and accumulate in the gut,” said Associate Professor Ariel.
Under the supervision of AIMS marine chemist Dr. Cherie Motti the new method was applied. It involves a sequence of chemical treatments designed to separate out swallowed plastic particles from plant and animal food remains as well as any sediment the turtle has swallowed during feeding. “We examined the gut of two green turtles using this new method, and even with this small sample set, found seven microplastics consisting of two plastic paint chips and five synthetic fabric particles. That’s in addition to also finding 4.5 m of nylon line and some soft plastic pieces entangled in the gut,” said Dr Motti.
“The new technique will increase our knowledge of the role plastic pollution plays in declining turtle health. But it has already highlighted the need for increased efforts in plastic pollution mitigation and reduction into the marine environment,” said JCU Professorial Research Fellow Dr Jon Brodie.
17 April 2018 from www.aims.gov.au
Thanks to movies and nature videos, many people know that bizarre creatures live in the ocean’s deepest, darkest regions. They include viperfish with huge mouths and big teeth, and anglerfish, which have bioluminescent lures that make their own light in a dark world.
However, the world’s deepest-dwelling fish – known as a hadal snailfish – is small, pink and completely scaleless. Its skin is so transparent that you can see right through to its liver. Nonetheless, hadal snailfish are some of the most successful animals found in the ocean’s deepest places.
Our research team, which includes scientists from the United States, United Kingdom and New Zealand, found a new species of hadal snailfish in 2014 in the Mariana Trench. It has been seen living at depths of almost 27,000 feet (8,200 meters). We recently published its scientific description and officially christened it Pseudoliparis swirei. Studying its adaptations for living at such great depths has provided new insights about what kinds of life can survive in the deep ocean.
We discovered this fish during a survey of the Mariana Trench in the western Pacific Ocean. Deep-sea trenches form at subduction zones, where one of the tectonic plates that form the Earth’s crust slides beneath another plate. They extend 20,000 to 36,000 feet deep below the ocean’s surface. The Mariana Trench is deeper than Mount Everest is tall.
Ocean waters in these trenches are known as the hadal zone. Our team set out to explore the Mariana Trench from top to bottom in an effort to understand what lives in the hadal zone; how organisms there interact; how they survive under enormous pressure created by six to seven miles of water above them; and what role hadal trenches play in the global ocean ecosystem.
Sending instruments to the ocean floor is pretty straightforward. Bringing them back up is not. Researchers studying the deep sea often use nets, cameras or robots connected to ships by cables. But a 7-mile-long cable, even if it is very strong, can break under its own weight.
We used free-falling landers – mechanical platforms that carry instruments and steel weights and are not connected to the ship. When we deploy landers, it takes about four hours for them to sink to the bottom. To call them back, we use an acoustic signal that causes them to release their ballast and float to the surface. Then we search for them in the water (each carries an orange flag), retrieve them and collect their data.
Hadal trenches are named after Hades, the Greek god of the underworld. To humans, they are harsh, extreme environments. Pressure is as high as 15,000 pounds per square inch – equivalent to a large elephant standing on your thumb, and 1,100 times greater than atmospheric pressure at sea level. Water temperatures are as low as 33 degrees Fahrenheit (1 degree Celsius). Yet, a host of animals thrive under these conditions.
Our team put down cameras baited with mackerel to attract mobile animals in the trench. At shallower depths, from approximately 16,000 to 21,000 feet (5,000-6,500 meters) on the abyssal plain, we saw large fish such as rattails, cusk eels and eel pouts. At the upper edges of the trench, below 21,000 feet, we found decapod shrimp, supergiant amphipods (swimming crustaceans), and small pink snailfish. This newly discovered species of snailfish that lives to near 27,000 feet (8,200 meters), is now the world’s deepest living fish.
At the trench’s greatest depths, near 36,000 feet (11,000 meters), we saw only large swarms of small scavenging amphipods, which are somewhat similar to garden pill bugs. Amphipods live all over the ocean but are highly abundant in trenches. The Mariana snailfish that we filmed were eating these amphipods, which make up most of their diet.
The Mariana Trench houses the ocean’s deepest point, at Challenger Deep, named for the HMS Challenger expedition, which discovered the trench in 1875. Their deepest sounding, at nearly 27,000 feet (8,184 meters), was the greatest known ocean depth at that time. The site was named Swire Deep, after Herbert Swire, an officer on the voyage. We named the Mariana snailfish Pseudoliparis swirei in his honor, to acknowledge and thank crew members who have supported oceanographic research throughout history.
Hadal snailfish have several adaptations to help them live under high pressure. Their bodies do not contain any air spaces, such as the swim bladders that bony fish use to ascend and descend in the water. Instead, hadal snailfish have a layer of gelatinous goo under their skins that aids buoyancy and also makes them more streamlined.
Hadal animals have also adapted to pressure on a molecular level. We’ve even found that some enzymes in the muscles of hadal fish are adapted to function better under high pressure.
Whitman College biologist Paul Yancey, a member of our team, has found that deep-sea fish use a molecule called trimethyl-amine oxide (TMAO) to help stabilize their proteins under pressure.
However, to survive at the highest water pressures in the ocean, fish would need so much TMAO in their systems that their cells would reach higher concentrations than seawater. At that high concentration, water would tend to flow into the cells due to a process called osmosis, in which water flows from areas of high concentration to low concentration to equalize. To keep these highly concentrated cells from rupturing, fish would have to continually pump water out of their cells to survive.
The evidence suggests that fish don’t actually live all the way to the deepest ocean depths because they are not able to keep enough TMAO in their cells to combat the high pressure at that depth. This means that around 27,000 feet (8,200 meters) may be a physiological depth limit for fish.
There may be fish that live at levels as deep, or even slightly deeper, than the Mariana snailfish. Different species of hadal snailfish are found in trenches worldwide, including the Kermadec Trench off New Zealand, the Japan and Kurile-Kamchatka trenches in the northwestern Pacific, and the Peru-Chile Trench. As a group, hadal snailfish seem to have found an unlikely haven in a place named for the proverbial hell.
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?
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.
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.
These species account for all but three of the 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.
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.
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.
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.
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.
Don’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.
Tiger sharks are one of the most successful large predators in the world’s oceans, but studying what they eat has been a challenge for researchers. Historically diet is studied through examining stomach contents, but scientists at the Australian Institute of Marine Science (AIMS) and collaborators are leading the way in understanding more about the feeding habits of sharks from their skin tissue. This allows us to learn about shark diet based on a quick non-lethal approach.
In a recent study, AIMS marine biologists Dr Luciana Ferreira, Dr Michelle Thums, Dr Mark Meekan and co-authors from a number of Australian universities, revealed their findings after examining the tissue samples of 273 tiger sharks from Western Australia to New South Wales and the Great Barrier Reef. Samples of blood and muscle tissue of tiger sharks showed information on the prey, position of individual sharks in the food chain, and even what type of habitat (coastal or offshore, seabed or open water) the animal had been feeding in.
Dr Ferreira said tiger sharks are large mobile animals and to ensure sustainable and resilient populations, we need better data on their feeding and behaviors. “In terms of predators, if we can understand the shark’s motivations and how they are using habitats, we can also understand their function within these habitats,” she said.
Difficulties involved in the direct observation of feeding behaviour of marine megafauna such as tiger sharks, has led to the use of alternative techniques to provide insights into the process of their foraging. One of the most common of these is the analysis of stable isotopes of carbon and nitrogen in their tissues, which can provide information on diet, feeding position in the food chain and interactions among different species, and their migratory movements. “Our analysis of stable isotopes shows that the functional role of tiger sharks in food-webs varied among different marine habitats we sampled along the tropical and temperate coasts of Australia,” Dr Ferreira said.
“Tiger sharks in Shark Bay and Ningaloo Reef in Western Australia, and on the Great Barrier Reef had long-term diets based in seagrass and reef-associated food webs. In these habitats they are focussed on turtles and dugong as prey. “In contrast, when sharks were sampled in more temperate habitats such the waters off New South Wales and southern Queensland, the composition of their tissues reflected a diet based on more pelagic [ocean-going] food webs, and they were focused on large fish. “Tiger sharks occupied roles at the top of food webs at Shark Bay in Western Australia and on the Great Barrier Reef, but not at Ningaloo Reef or off the coast of NSW. “This means the local environment and prey community appear to be the most important determinants of the diet of tiger sharks.” Dr Ferreira said the research confirmed the role of tiger sharks in Australian coastal ecosystems as opportunistic, flexible predators.
The research paper ‘The trophic role of a large marine predator, the tiger shark Galeocerdo cuvier’ is published in Nature Scientific Reports.
9 November 2017, Australian Institute of Marine Science, 2017
Indo-Pacific bottlenose dolphins (Tursiops aduncus) are a regular sight in the waters around Australia, including the Bunbury area in Western Australia where they attract tourists.
The dolphin population here, about 180km south of Perth, has been studied quite intensively since 2007 by the Murdoch University Cetacean Unit. We know the dolphins here have seasonal patterns of abundance, with highs in summer/autumn (the breeding season) and lows in winter/spring.
But in winter 2009, the dolphin population fell by more than half.
This decrease in numbers in WA could be linked to an El Niño event that originated far away in the Pacific Ocean, we suggest in a paper published today in Global Change Biology. The findings could have implications for future sudden drops in dolphin numbers here and elsewhere.
The El Niño Southern Oscillation (ENSO) results from an interaction between the atmosphere and the tropical Pacific Ocean. ENSO periodically fluctuates between three phases: La Niña, Neutral and El Niño.
During our study from 2007 to 2013, there were three La Niña events. There was one El Niño event in 2009, with the initial phase in winter being the strongest across Australia.
Coupled with El Niño, there was a weakening of the Leeuwin Current, the dominant ocean current off WA. There was also a decrease in sea surface temperature and above average rainfall.
ENSO is known to affect the strength of the south-ward flowing Leeuwin Current.
During La Niña, easterly trade winds pile warm water on the western side of the Pacific Ocean. This westerly flow of warm water across the top of Australia through the Indonesian Throughflow results in a stronger Leeuwin Current.
During El Niño, trade winds weaken or reverse and the pool of warm water in the Pacific Ocean gathers on the eastern side of the Pacific Ocean. This results in a weaker Indonesian Throughflow across the top of Australia and a weakening in strength of the Leeuwin Current.
The strength and variability of the Leeuwin Current coupled with ENSO affects species biology and ecology in WA waters. This includes the distribution of fish species, the transport of rock lobster larvae, the seasonal migration of whale sharks and even seabird breeding success.
The question we asked then was whether ENSO could affect dolphin abundance?
These El Niño associated conditions may have affected the distribution of dolphin prey, resulting in the movement of dolphins out of the study area in search of adequate prey elsewhere.
This is similar to what happens for seabirds in WA. During an El Niño event with a weakened Leeuwin Current, the distribution of prey changes around seabird’s breeding colonies resulting in a lower abundance of important prey species, such as salmon.
In southwestern Australia, the amount of rainfall is strongly connected to sea surface temperature. When the water temperature in the Indian Ocean decreases, the region receives higher rainfall during winter.
High levels of rainfall contribute to terrestrial runoff and alters freshwater inputs into rivers and estuaries. The changes in salinity influences the distribution and abundance of dolphin prey.
This is particularly the case for the river, estuary, inlet and bay around Bunbury. Rapid changes in salinity during the onset of El Niño may have affected the abundance and distribution of fish species.
In 2009, there was also a peak in strandings of dead bottlenose dolphins in WA (between 1981-2010), but the cause of this remains unknown.
Of these strandings, in southwest Australia, there was a peak in June that coincided with the onset of the 2009 El Niño.
Specifically, in the Swan River, Perth, there were several dolphin deaths, with some resident dolphins that developed fatal skin lesions that were enhanced by the low-salinity waters.
Our study is the first to describe the effects of climate variability on a coastal, resident dolphin population.
We suggest that the decline in dolphin abundance during the El Niño event was temporary. The dolphins may have moved out of the study area due to changes in prey availability and/or potentially unfavourable water quality conditions in certain areas (such as the river and estuary).
Read more: Explainer: El Niño and La Niña
Long-term, time-series datasets are required to detect these biological responses to anomalous climate conditions. But few long-term datasets with data collected year-round for cetaceans (whales, dolphins and porpoises) are available because of logistical difficulties and financial costs.
Continued long-term monitoring of dolphin populations is important as climate models provide evidence for the doubling in frequency of extreme El Niño events (from one event every 20 years to one event every ten years) due to global warming.
With a projected global increase in frequency and intensity of extreme weather events (such as floods, cyclones), coastal dolphins may not only have to contend with increasing coastal human-related activities (vessel disturbance, entanglement in fishing gear, and coastal development), but also have to adapt to large-scale climatic changes.
Kate Sprogis, Research associate, Murdoch University; Fredrik Christiansen, Postdoctoral Research Fellow, Murdoch University; Lars Bejder, Professor, Cetacean Research Unit, Murdoch University, Murdoch University, and Moritz Wandres, Oceanographer PhD Student, University of Western Australia
9 October 2017