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I would like to know to what extent regenerative agriculture practices could play a role in reducing carbon emissions and producing food, including meat, in the future. From what I have read it seems to offer much, but I am curious about how much difference it would make if all of our farmers moved to this kind of land management practice. Or even most of them. – a question from Virginia
To identify and quantify the potential of regenerative agriculture to reduce greenhouse gas emissions, we first have to define what it means. If regenerative practices maintain or improve production, and reduce wasteful losses on the farm, then the answer tends to be yes. But to what degree is it better, and can we verify this yet?
Let’s first define how regenerative farming differs from other ways of farming. For example, North Americans listening to environmentally conscious media would be likely to define most of New Zealand pastoral agriculture systems as regenerative, when compared to the tilled fields of crops they see across most of their continent.
If milk and meat-producing animals are not farmed on pasture, farmers have to grow grains to feed them and transport the fodder to the animals, often over long distances. It’s hard to miss that the transport is inefficient, but easier to miss that nutrients excreted by the animals as manure or urine can’t go back to the land that fed them.
Returning nutrients to the land really matters because these build up soil, and grow more plants. We can’t sequester carbon in soil without returning nutrients to the soil.
New Zealand’s style of pastoral agricultural does this well, and we’re still improving as we focus on reducing nutrient losses to water.
First, the animals that efficiently digest tough plants – including cows, sheep, and goats – all belch the greenhouse gas methane. This is a direct result of their special stomachs, and chewing their cud. Therefore, farms will continue to have high greenhouse gas emissions per unit of meat and milk they produce. The recent Intergovernmental Panel on Climate Change (IPCC) report emphasised this, noting that changing diets can reduce emissions.
The second problem is worst in dairying. When a cow lifts its tail to urinate, litres of urine saturate a small area. The nitrogen content in this patch exceeds what plants and soil can retain, and the excess is lost to water as nitrate and to the air, partly as the powerful, long-lived greenhouse gas nitrous oxide.
Regenerative agriculture lacks a clear definition, but there is an opportunity for innovation around its core concept, which is a more circular economy. This means taking steps to reduce or recover losses, including those of nutrients and greenhouse gases.
The price premium and regulation linked to certification can limit the redesign of the organic agricultural systems to incremental improvements, limiting the inclusion of regenerative concepts. It also means that emission studies of organic agriculture may not reveal the potential benefits of regenerative agriculture.
Instead, the potential for a redesign of New Zealand’s style of pastoral dairy farming around regenerative principles provides a useful example of how progress might work. Pastures could shift from ryegrass and clover to a more diverse, more deeply rooted mix of alternate species such as chicory, plantains, lupins and other grasses. This system change would have three main benefits.
The first big win in farming is always enhanced production, and this is possible by better matching the ideal diet for cows. High performance ryegrass-clover pastures contain too little energy and too much protein. Diverse pastures fix this, allowing potential increases in production.
A second benefit will result when protein content of pasture doesn’t exceed what cows need to produce milk, reducing or diluting the nitrogen concentrated in the urine patches that are a main source of nitrous oxide emissions and impacts on water.
A third set of gains can result if the new, more diverse pastures are better at capturing and storing nutrients in soil, usually through deeper and more vigorous root growth. These three gains interrelate and create options for redesign of the farm system. This is best done by farmers, although models may help put the three pieces together into a win-win-win.
Whether you’re interested in local beef in Virginia, or the future of New Zealand’s dairy industry, the principles that define regenerative agriculture look promising for redesigning farming to reduce emissions. They may prove simpler than agriculture’s wider search for new ways of reducing greenhouse gas emissions, including genetically engineering ryegrass.
We’ve arranged to meet in a gravel car park at the foot of Mt Majura, a darkening wedge above us in the dusk. My daughter and I wait in the car. It’s winter. A woman passes along the nearby pavement, guiding her way by torchlight. Canberra’s streets are kept dim, I learned recently, for the sake of astronomers at nearby Mt Stromlo observatory. In the decade I’ve lived here, I’ve had an ambivalent relationship with Canberra, but the idea of a city that strikes bargains with stargazing scientists to restrict light pollution leaking skyward is endearing.
There are other endearing things. One of them is the amount of bushland interspersed throughout the urban landscape. You can be in the middle of suburbia one minute and bushwalking on nearby Black Mountain, Mt Majura or Mt Ainslie ten minutes later. This kind of mixed landscape is ideal for the citizen science project we’re about to launch into this evening, as soon as the co-ordinator of the ACT and Region Frogwatch Program, Anke Maria Hoefer, arrives for our first training session.
The program runs a community-based annual Frog Census framed against a rapid global decline in frog numbers over the past four decades and the extinction of many frog species. The census began in 2002, and the resulting long-term dataset on the abundance and distribution of local frogs has enabled additional research activities including a climate change project. We’ll take part in the latter, which monitors behavioural shifts in frogs through recording their calls at particular sites each week from June until October.
We’re here for a few reasons. One is to get a lived sense of climate change in our immediate urban surroundings. Plus, I want to make a contribution, however small, to the huge dilemma of climate change and its impacts; give my 13-year-old daughter a taste of scientific fieldwork in case it appeals to her; get to know our local surroundings better; and, as a writer, to think about practices that don’t simply observe or contemplate place but also participate in constructive activities at those same locales.
Numerous commentators have observed that the vast and intangible scale of climate change may be an impediment to more people taking action over our warming atmosphere. We know through the science that climate is shaped by the working of the entire planetary system – the earth’s interactive ocean, atmosphere, land and ice systems all linked to human activity. Depending on where you live, (but not in the Pacific Islands, the deltas of Bangladesh, Arctic Canada, or drought-stricken rural Australia), its impacts can seem far-removed from our own lives and the places we know best and care most about. With care, often, comes action. What can seem an amorphous, far-fetched threat is brought closer to home through studies such as Frogwatch.
The project studies the impact of climate change on phenology, or seasonal behaviour. Most frogs only call during the mating season, which is triggered by temperature and rainfall. Different species mate at different times and volunteers record the onset of mating calls from winter breeders (whistling tree frog and common eastern froglet), early and mid-spring breeders (spotted grass frog, plains froglet, striped marsh frog and smooth toadlet), and late spring to summer breeders (eastern banjo frog and Peron’s tree frog).
Frogs are known as an “indicator species” for water quality and local ecosystem health. With their permeable, membranous skin, through which respiratory gases and water can pass, and their shell-less eggs laid in water, they are sensitive to even low concentrations of pollutants in water and soils. In this study, frogs give a different kind of warning – as they begin calling earlier in the season, they reveal and give voice to the warming climate we now all inhabit.
The project is fortunate enough to be able to build upon weekly counts of calling frogs by ecologist Will Osborne during the 1980s and 1990s in the Canberra region. Effects of climate change can be incremental. They can also be non-linear, as scientist Pep Canadell explained to me in a recent interview. “Climate change expresses itself through extremes. It’s not a linear relationship of impacts,” he said.
This mixture of incremental change and unpredictable “expressions” can be difficult to record in the short term. With this in mind, the Frogwatch project builds on Osborne’s historical data along with the Frog Census data to chart changing trends. A preliminary comparison reveals that the breeding season of some local frog species might be commencing up to six weeks earlier than 40 years ago.
A sonic world
Headlights sweep into the car park and Anke Maria arrives with a visiting German student who is also researching frogs. Anke Maria is a whirlwind of talk and activity, honing in on my daughter as we zip our down jackets, pull on beanies and gloves, switch on torches and head up a gravel fire trail toward the first dam, known as FMC200. Only metres later we stop at the base of a narrow drainage gully. It’s been a dry winter, but with a patch of recent rainfall a miniature sump-like drainage area at the base of the gully is alive with frog calls.
“That’s Crinia signifera,” Anke Maria explains, making what seems a perfect imitation of its repetitive call. “How would you describe it?” she asks. My daughter turns to me. The call is repetitive, creaking. We struggle to think of descriptions. It’s like trying to put a flavour into words.
“Who do you think is calling? The male or female?” Anke Maria asks. My daughter pauses, pondering. “The female,” she hazards a guess. “Good try,” says Anke Maria, “but only the male frog calls. Except when the female makes a warning call.” She imitates this staccato warning sound. “And why do you think the males are calling?” Again my daughter pauses to consider.
We continue walking up the gravel slope amid shadowy shapes of eucalypt trees, a tangle of gorse and acacia undergrowth, a row of looming metal electricity pylons strung along the lower contour lines of Mt Majura.
“They could be hungry or they found food,” my daughter replies.
“Good thinking, but they’re calling to attract a girlfriend. And do you know, scientists think that each frog species can only hear the calls of their own species. It’s like tuning into a radio station. There are many different stations, but we can only tune into one at a time. A female whistling tree frog can only hear a male whistling tree frog, a female corroboree frog can only hear a male corroboree frog.”
They recognise the frequency and intensity or pitch of the call, she explains, and also the pattern of the call or its pulse structure. “This helps the female find a mate from their own species and not get confused by other frogs.”
We ponder this sonic world where one species can be deaf to another, turn left down a narrow walking track, torchlight bobbing along with our footsteps, illuminating tussocks of grass, fallen branches, shrubs, stones, until we reach the dam. “This is for you,” Anke Maria passes a thermometer. “You do it,” she tells my daughter. First we record the ambient temperature then my daughter squats at the edge of the water, waving the thermometer gently through the shallows. We note the weather: light cloud cover, low breeze. We estimate the dam’s surface area and depth. Then our small group falls silent as Anke Maria switches on her phone audio-recorder.
For three minutes we hold still and listen. There’s the low hum of the city below, an ambulance siren swells and recedes, distant traffic, the shuffle of our down jackets as we try not to move, someone sniffs in the chill winter air – and the frogs. You can hear them interspersed across space, some close, some farther away, among vegetation rather than water. Because of Anke Maria’s explanation, I understand now these are not call-and-response sounds. They are invitations, serenades, statements of presence, lures. Sometimes the calls come in a cluster, other times at staggered unpredictable intervals. There are at least two species here, I guess. In the distance, a mopoke calls.
When Anke Maria switches off her phone, we relax into movement again. As we walk towards FMC210, our second dam, she tells us we’ve just heard a whistling tree frog (Litoria verreauxii). “How would you describe his call?” Anke Maria asks.
My daughter decides on a stick dragged across a rough, hollow surface. Anke Maria makes the call. Her imitations are pitch perfect, an art form. She will be the one who checks the recordings that non-specialist volunteers send in weekly, uploaded to the Frogwatch website. We will make our guesses at species we’ve heard, but she will verify with her trained ear, a labour-intensive task.
In our information pack is a CD of local frog species. When we get home we lie on the carpet and listen, the house filled with frog noise.
A new frog
A week later, on our first trip into the dark alone, the evening is silvered and rigid with frost, as if everything is held together in some different, more metallic way. It’s three below zero and falling. Our breath steams, our boots crunch, the bush is still. I sense something in a dead tree ahead before I see it, a tawny frogmouth, grey, motionless, an outcropping like a broken limb. We pause several steps away and it regards us, head half swivelled, a little tuft of feathers at the base of its beak.
The following week, on our descent from the dams, once again a frogmouth is in the same tree. A second bird perches a few metres away. They are bound together in some mute, still business. They survey us. We move on with subdued steps. Beyond the birds, the first row of suburban houses begins. We thread our way back to the car with a sense of secrecy and adventure, past back fences, patches of bright window, catching fugitive glimpses of other people’s lives through a half-open door, a crack in a curtain, the blue flicker of TV light.
At the dams we make our recordings. Air temperature, water temperature, ascending over the weeks. On the far side of Mt Majura lies the airport. Often early into a sound recording, a plane takes off, blotting out all other sound. Ecologist Will Osborne tells me he has observed that the aeroplane sound seems to overlap the call parameters (pitch and pulse structure) of the Common Eastern Froglet. Whenever a plane goes over, the froglet stops calling while other species continue – machine and creature competing on the airwaves.
When I upload the recordings, Anke Maria responds and confirms (or not) my guesses at species. You should soon hear Crinia parinsignifera she emails, so keep your ears peeled for a high pitch narky baby cry!
Her enthusiasm is infectious, her aural sketches vivid, memorable. When we hear the new frog, I know exactly what it is. Everyone on the team, each with sites to attend scattered across Canberra, has been waiting for this particular call.
It might show that an early spring breeder is shifting its season into winter. This minor-sounding alteration has a cascade of flow-on effects. Frogs stagger breeding seasons, giving each species its portion of acoustic space to call, breed, then when eggs hatch into tadpoles to feed (a mode of “time sharing” water and its resources). If seasons shift, merge and overlap, competition for resources intensifies, and survival can be jeopardised.
But this year it’s a cold, dry winter. This telling species, Crinia parinsignifera, is calling two weeks later than last year (when it called early). Meanwhile northern Australia is experiencing its warmest July on record. Non-linear. As the monitoring season progresses, dam levels drop. By the end of October, waters have fallen almost silent.
Will Osborne sends an email around, explaining that cold nights and low water levels will make it hard to interpret this season’s counts. “Most species feel insecure about going out onto that exposed mud and trying to find a call site or searching for mates! It will be a big rush when the weather warms and we get good rains – the calling sequence could be condensed this year which will be interesting…”
Many volunteers join Frogwatch because they want to participate in a hands-on, climate change-related study with real life applications. “They highly value the opportunity to be involved in climate change actions,” Anke Maria says. She captures one of the dilemmas of our times. Many people want to take action but are unsure how. As artist Natalie Jeremijenko observed): “What the climate crisis has revealed to us is a secondary, more insidious and more pervasive crisis, which is the crisis of agency, which is what to do.” Citizen science gives volunteers an opportunity to do something.
Studies that chart the impacts of climate change here-and-now disrupt the assumption that effects will occur in a distant future or at some remote geographic location (melting ice caps, apocalyptic cities under 20 metres of water). Instead, they start to build a picture of measurable effects experienced at the current level of 1°C warming above pre-industrial levels – let alone at 2°C or above, which is what we’re committing to based on current emissions rates. In the Canberra region alone, studies are being conducted into impacts of global warming on urban lizard species (who reside next to the local DFO) and alpine pygmy possums.
At a broader scale, Pep Canadell has observed major ecological transformation in Australia that occurred with a 1.2°C increase during the last El Niño. He calls the El Niños a “window into the future because they bring all this heat and put the world where it may be in 30 or 20 years’ time.”
“These ecological signs are unprecedented, all in this little window of a warmer world that the El Niño brought for us,” said Canadell during our interview. He went on to list even more signs. “For some reason these things don’t go through the media enough because of … whatever,” he added.
The Frogwatch project enables volunteers to dwell in an everyday way with such dispersed ecological signals, which, connected together with other studies, provide a larger picture of both current and future impacts. Volunteers are privileged to make their small citizen science contribution to understanding and recording these signs better.
Unfortunately, just as I completed this article, the Frogwatch Program discovered that its funding from the ACT Government was not renewed in the 2018–19 budget. Without core funding, the organisation and its annual Frog Census will cease. The enthusiasm of volunteers will help to collect another season’s data for the climate change study but it too is under serious threat unless alternative funding can be sourced.
When our monitoring season finished last year, I asked my daughter whether she wanted to do it again. “Yes,” she replied without hesitation. “What did you like most about it?” I asked. “I don’t know,” she said, “it was just fun.” And so, as Canberra’s heavy frosts set in, we have begun again, treading up towards FMC200, waiting for frog calls to begin.
Saskia Beudel’s full interview with Pep Canadell will be published in December 2018 in the journal Weber.
Research in Australia and other countries indicates that, in the distant geological past, asteroids as large as Eros (about 34.4km long and 11.2km wide) have impacted Earth. These have triggered major changes in the structure and evolution of the crust and mantle, as I’ve written about before.
The terrestrial planets of the inner solar system – Mars, Earth, Venus and Mercury – are all affected by asteroids deflected from the asteroid belt, located between Mars and Jupiter, and by comets falling off the Kuiper belt beyond Neptune.
Many of these impact craters are clearly seen on Mars and Mercury as well as on our Moon. Venus too has its craters, but its thick atmosphere obscures these.
When Earth is viewed from space, it displays little or no cratering despite also being located in the trajectory of these asteroids and comets.
But this impression is apparent rather than real. Many of the impact scars are covered or masked due to the dynamic nature of Earth and the oceans that extend over some two-thirds of the planet’s surface. The masking processes include the accretion and subduction of tectonic plates as well as intensive erosion processes.
It was not until about 1981 that the scientific community began to recognise the significance of extraterrestrial impacts for the mass extinction of species about 66 million years ago, which wiped out the dinosaurs and many other groups.
The American scientists Louis and Walter Alvarez and their colleagues had unearthed a telltale iridium-rich sedimentary layer around the 66 million-year-old Cretaceous-Tertiary boundary at Gubbio, Italy. The element iridium, typically enriched in asteroids, is a signature within sediments for material from a meteorite impact.
The discovery re-established the idea that catastrophes shaped much of Earth’s history, a theory originally promoted by the French zoologist Georges Cuvier.
Impacts on the Earth
Beyond forming craters, the impact of large asteroids on Earth resulted in the formation of structural domes due to elastic rebound of the crust. Examples include the Vredefort dome in South Africa and the buried Woodleigh dome under and east of Shark Bay in Western Australia.
The impacts also caused major seismic activity and faulting, large tsunami events, ejection of masses of particles and dust, and – as mentioned earlier – in some instances the mass extinction of species due to rapid environmental changes.
The asteroid impact record on Earth is thus to a large extent concealed and the subject of an extensive search using structural, geophysical, geochemical and other methods.
Since many impact records are covered by the oceans or were eroded, old stable parts of the Earth crust, named “cratons”, are the best places to look. This is where the scars of ancient asteroid impacts are preserved and can be found, including craters and their deep-seated roots and rebound dome structures.
The criteria applied for recognition of asteroid impact structures and meteorite craters allowed the identification of at least 38 confirmed impact structures on the Australian continent and surrounding continental shelf.
There are an additional 43 examples of exposed and buried circular ring and dome features, many of which are of possible or probable impact origin.
Examples of exposed confirmed impact structures include Gosses Bluff in the southern Northern Territory, Shoemaker in central Western Australia, and Acraman and Lawn Hill in northwestern Queensland.
A Google Earth image of the central ring of the Gosses Bluff impact structure, central Australia, Northern Territory. It is 14km in diameter and was formed around 142 million years ago.
A Google Earth image of the Shoemaker impact structure, Nabberu Basin, in Western Australia. It is 30km in diameter and was likely formed around 1,630 million years ago.
A Google Earth image of the centre of the Acraman impact structure in southern South Australia. It is 90km in diameter and was formed around 590 million years ago.
A Google Earth image of the centre of the Lawn Hill impact structure in northwestern Queensland. It is is 18km in diameter and was formed more than 515 million years ago.
The impact record of Australia thus includes exposed impact structures, buried impact structures, meteorite craters and geophysical ring anomalies of unproven origin.
Examples of large geophysical multi-ring features – total magnetic intensity anomalies, circular gravity anomalies and seismic domes – include probable buried twin impact structures in the Warburton Basin in northeast South Australia, a confirmed buried impact structure at Woodleigh in WA, and confirmed buried impact structures at Tookoonooka and Talundilly in the Eromanga Basin in southwest Queensland.
Fallout of asteroid impacts
Structures and craters caused by asteroid impacts are not the only thing we find. In the Australian landscape there are also the rock fragments and melt drops derived from clouds ejected from the impact craters.
The melt drops, condensed from impact-ejected vapour, are termed “microkrystites”. These are recognised by their radiating quench (cooling) textures and abundance of platinum group element anomalies.
In at least one instance the evidence suggests that an impact by a cluster of large asteroids resulted in an abrupt transformation of crustal structure on the Pilbara, northwestern Australia, as well as the Barberton greenstone belt in South Africa, from a granite/greenstone system to semi-continental crustal environment.
Between 3.26 and 3.24 billion years ago these impacts caused a sharp tectonic uplift and magmatic activity, leading to to an onset of semi-continental crustal conditions.
Thus, far from being free from impacts, the Australian landscape has been shaped many times over millions and billions of years by asteroids falling to Earth.
As studies of Australian impact structure and impact ejecta progress, the critical role of asteroid impacts in the early evolution of the Earth and in the development of the Australian continent are becoming clearer.
Rising ocean temperatures may result in worldwide change for shallow reef ecosystems, according to research published yesterday in Science Advances.
The study, based on thousands of surveys carried out by volunteer scuba divers, gives new insights into the relationship of fish numbers to water temperatures – suggesting that warmer oceans may drive fish to significantly expand their habitat, displacing other sea creatures.
The study draws from Reef Life Survey, a 10-year citizen science project that trains volunteer scuba divers to survey marine plants and animals. Over the past ten years, more than 200 divers have surveyed 2,406 ocean sites in 44 countries, creating a uniquely comprehensive data set on ocean life.
Lead author Professor Graham Edgar, who founded Reef Life Survey, said the unprecedented scope of their survey allowed them to investigate global patterns in marine life. The abundance of life in warm regions (such as tropical rainforests and coral reefs) has long intrigued naturalists. At least 30 theories have been put forward, but most studies have been based on relatively limited surveys restricted to a single continent or group of species.
By tapping into the recreational scuba diving community, Reef Life Survey has vastly increased the amount of information researchers have to work with. Professor Edgar and his colleagues provide one-on-one training to volunteers, teaching them how to carry out comprehensive scans of plants and animals in specific areas.
Dr Adriana Vergés, a researcher at the University of New South Wales specialising in the impact of climate change on ocean ecosystems, said that the Reef Life Survey has already substantially improved our understanding of the marine environment.
“For example, Reef Life Survey data has greatly contributed to our understanding of the factors that determine the effectiveness of effectiveness of marine-protected areas worldwide. The team have made all their data publicly available and more and more research is increasingly making use of it to answer research questions,” she said.
Some of the divers have been working with Reef Life Survey for a decade, although others participate when they can. One volunteer, according to Professor Edgar, was so inspired by the project that he began a doctorate in marine biology (he graduated this year).
Warming oceans means fish on the move
One of the important insights delivered by the Reef Life Survey datatbase is the relationship between water temperature and the ratio of fish to invertebrates in an ecosystem. Essentially, the warmer the water, the more fish. Conversely, colder waters contain more invertebrates like lobster, crabs and shrimp.
Professor Stewart Frusher, director of the Centre for Marine Socioecology at the University of Tasmania (and a former colleague of Professor Edgar) told The Conversation that he believes we will see wide-scale changes in fish distribution as climate change warms the oceans.
“Species are moving into either deeper water or towards the poles. We also know that not all species are moving at the same rate, and thus new mixtures of ecosystems will occur, with the fast-moving species of one ecosystem mixing with the slower moving of another,” he said.
As species migrate or expand into newly warmed waters, according to Professor Frusher, they will compete with and prey on the species already living in that area. And while it’s uncertain exactly how disruptive this will be, we do know that small ecosystem changes can rapidly lead to larger-scale impacts.
In order to predict and manage these global changes, scientists need reliable and detailed world-wide data. Professor Frusher said that, with research funding declining, scientists do not have the resources to monitor at the scales required.
“Well-developed citizen science programs fill an important niche for improving our understanding of how the earth is responding to change,” he said.
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?
What happened during the El Niño?
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.
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.
What does all this mean?
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).
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.