Ocean currents
Type
Article
Category
Climate change

In the wake of a Leviathan: The Eastern Australian Current and the future of our oceans

What would an ocean be without a monster lurking in the dark? It would be like sleep without dreams.  – Werner Herzog

 

The sparkling stretch of an open ocean has long inspired monstrous fantasies. Bored Renaissance cartographers filled the blue voids on their maps with imperilled ships and winding fishtails, scaled giants to embody the ocean’s power. The expanse of the Pacific was filled with spirits both chaotic and benign, pulling at the imagination like a siren to a sailor. Although modern mapping has done away with aquatic blind spots and the Leviathans that dwell within, oceanographic data has revealed the real giants in our charts.

Blue arrows curve their way around the continents, but these symbols cannot strip the power that the great currents hold. With no land to hinder them, strong winds have free rein over the open ocean. Winds are created by the constant battle between warm and cool air, and this same principle applies to the movement of warm and cold waters.

Between the Americas, Asia and Australia, there are three major whirls that spin the Pacific’s clockwork currents. These are the gears that drive what we know as the East Australian Current (EAC), most famous perhaps as a plot device in Disney-Pixar’s film Finding Nemo. Its serpentine path winds down from the equator and brushes Australia’s side, carrying nutrient-rich water from the deep sea to the southern parts of the Great Barrier Reef, past the coastlines of New South Wales, before sweeping back out towards New Zealand.

Like a cold-blooded animal emerging from hibernation, the EAC system gets more energetic when it’s hot. In summer, the EAC kicks into life, and pulses of warm water stream down Australia’s coast. In winter, when the air cools and the Pacific winds calm, the EAC retreats. This is how it’s been for centuries. The marine life that inhabits this system is used to it, use it to their advantage as a migration highway between breeding and feeding grounds – just like the surfer dude sea turtles that help Marlin and Dory on their way to Sydney. But as the air becomes hotter as a result of climate change, the South Pacific winds are getting stronger, for longer. The wind-up sea serpent that is the EAC kicks with more vigour and force, and the creatures it carries are dragged in its wake. Fish from all along Australia’s coastline are finding themselves pushed further south.

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Curtis Champion is a young marine biologist who grew up in a NSW town called Forster, about 4 hours’ drive north of Sydney. He’s every bit the beaming, blonde-haired surfer, and says he’s spent much of his life with his head underwater, like most folks from the seaside town. ‘The East Australian Current is very present there … anything north of Sydney can generally be described as highly affected by the EAC,’ Curtis explained. Forster is full of fishermen, divers and surfers who spend their lives in and around the water, eating its harvest, and decorating their homes in tribute to their marine identity.

Curtis believes this relationship with marine life makes Australians culturally well-equipped to observe and act on climate change. ‘Speaking with people from my hometown, they’ve most certainly seen the arrival of new fish,’ he explains, ‘particularly those from the southern Barrier Reef.’  His friends in Forster have caught coral trout, which fifty years ago would’ve been ‘unheard of’, and Curtis has seen surgeonfish and rabbitfish (two algae-eating reef species) far south of their usual range while diving at his local spots.

While the EAC once penetrated only as far South as Sydney, in recent years this giant has begun to ripple as far south as Hobart, bringing all kinds of submarine migrants in tow. Following the poleward migration of the fish he studies, Curtis moved down to Tasmania himself, devoting his research to the kingfish (Seriola lalandi). Where better to study them than Hobart — the world’s southernmost state capital — where this species has headed? Curtis’ research is based on records created by ‘citizen scientists’, ordinary people with an interest in collecting and sharing data under a NSW government fish tagging initiative that began in the 1970s.

Curtis explains: ‘They give out tags to fishermen who are keen to participate in a catch and release fishing practice, so every time a fish gets tagged, the NSW government get an alert and there’s a large database as a result. While the NSW government is responsible for administering this program, the tagged fish often turn up in far-flung places, and have been recorded far from home as New Zealand. But generally, Curtis has found, kingfish like to live in waters of 20-21 degrees Celsius. The data he uses only goes back to 1996, when satellites started recording ocean temperature, but even in that short space of time, the fish’s suitable habitat has stretched south by about 200 kilometres.

In 2016, an article in Hobart’s local paper The Mercury announced: ‘Warmer waters makes Tassie a hotspot for new fishy friends’, reporting on record catches of NSW table fish that summer – snapper, yellowtail kingfish, King George whiting, and broadbill swordfish. The article noted a number of other unusual sightings associated with the EAC: ‘several nautilus shells and nutmeg sea snails around Port Arthur, a coconut at Marion Bay, a Balmain bug in the shallows at Tinderbox, blue bottles at the very bottom of South West National Park, [and] two venomous yellow-bellied sea snakes.’

‘[Tasmania’s] got a new kid on the block, and it’s a highly welcomed newcomer because it’s tasty and delicious,’ says Curtis. ‘There’s already a small but rapidly growing recreational fishery growing in Tasmania.’ But whether the arrival of kingfish and other tropical species is really such good news or not depends on who you ask. The urchin barrens growing along Tasmania’s southern coastline have devastated lobster habitat, for instance.

‘You might see lobster fishermen who love to dive for a feed of rock lobster, and they’re really concerned and worried because they know now that the macroalgae forests they loved to share with their families, are now being degraded,’ says Curtis. ‘But also there’s fishermen I’ve spoken to in Tasmania, line fishermen, who are really enjoying targeting species like snapper or kingfish, and they’re quite positive, because climate change is now opening up fishing opportunities for them on their doorstep.’

Likewise, ‘tropicalised’ waters off Sydney sound idyllic, but there’s reason to feel uneasy about the side-effects of warmer waters. Though some Great Barrier species have already begun relocating southwards, Curtis doesn’t anticipate an easy migration for Australia’s postcard underwater Eden, the Great Barrier Reef. Coral can only ‘move’ over many generations of spawning, and even then, the polyps require sea water with high levels of calcium to grow exoskeletons, which southern Australian waters generally lack.

‘It takes so long for these ecosystems to build up and really become biodiverse,’ says Curtis. ‘[The Great Barrier Reef] is just like an old growth forest – you walk in and it’s got this fantastic depth about it, whereas if a new reef system were to establish … it won’t be the same Great Barrier Reef that we know and love.’

As more hot air is injected into this system, the EAC will only get more powerful. But when it comes to who will survive under these new conditions, we really are heading into unknown territory, with marine-based economies – fishing, tourism – thrown into precarity. While species have always changed and adapted to new conditions in the past, man-made climate change is happening more rapidly than any prior shifts.

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At the Institute of Marine and Antarctic Studies, Curtis is mentored by Gretta Pecl, a Tasmanian marine biologist who helped establish the field of study now known as ‘Species On The Move’. This brings different disciplines together to focus on this climate change-induced mass migration – both on land and underwater. In temperate zones like Tasmania, Gretta and Curtis hope the lost fisheries – lobster, abalone, etc. – will be replaced by an influx of more tropical species, like the kingfish. Conversely, those species are likely to be displaced from their equatorial, tropical homes as the EAC intensifies and the ocean acidifies.

Gretta paints a striking picture of these future oceans. She expects that squid and jellyfish will move in to fill the void. These opportunistic marine animals can grow fast, reproduce quickly, and take advantage of the changing conditions. Already these tentacled entrepreneurs are multiplying. Jellyfish have begun their takeover of the world’s oceans by sliding into polluted and low oxygen waters to evade predators, clogging up power plants and fishing hauls. This is only expected to continue as waters become uninhabitable for other marine life forms. Adelaide researchers have determined that squid and octopus populations have boomed worldwide since the 1950s – a problem for their prey species, since cephalopods can eat 30% of their body weight daily. They predict that in a future of warmer, more hostile oceans, squid fisheries will become increasingly important, so long as they still have enough to eat and we adopt sustainable fishing practices.

‘For every winner, there’ll be a loser,’ says Gretta. ‘We might be getting new species coming south, but the tropics are losing them … they’re going to end up with less species there, because there’ll be fewer that can handle those kinds of limits.’

While the ecological gaps left by climate change will not be left entirely vacant, there’s no doubt our oceans will soon look very different from the mature, diverse systems we’re used to.

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When the IPCC’s devastating 2018 report on climate change was released, Curtis was at the Australian Society for Fish Biology conference in Melbourne. Scientists gathered at a public forum to talk climate change, and the new report was on everyone’s lips. He says:

The conversation turned to, ‘well, shit, how are we going to reduce emissions to limit warming to a degree and a half?’ It got down to the practical discussions quite quickly. There’s probably a lot of huge behavioural changes that would have to happen to limit it.

According to the Intergovernmental Panel on Climate Change, even if carbon emissions had stopped in the year 2000, the Earth’s average temperature would still rise another 0.6 degrees Celsius in the next century. Curtis thinks a combination of adaptation and conservation may be our only option. At the end of 2017, he says, we are already committed to some level of mass marine migration, and the flow-on effects it entails:

Ultimately, we need political will that engages people from all corners of the globe and basically contributes to less greenhouse gas pollution. But in the meantime, we could build seasonal forecasts for species shifts and try to develop adaptation strategies around those forecasts.

A major issue is food security, as is the case for the fishing communities affected by the EAC.

‘We need to still try and be using what we can, but what’s sustainable and what isn’t might change in terms of conservation,’ adds Gretta. ‘I think there’s going to be big discussions on ethics and values, and what do we want out of our marine systems.’ For Tasmanians, that may mean turning to more tropical fisheries to replace the lobster and abalone industry on which the state’s economy is built. For those on Australia’s east coast and in the equatorial regions of the Pacific, squid fisheries may become increasingly important. For coastal people, climate change is not some abstract computer model. As Curtis puts it, ‘it’s a fish that you’ve never seen, caught in a place you’ve always been.’

‘It’s a really tricky situation [to respond to] because it ties into everybody’s values, and all these people that could or should be having a say will have different values,’ says Gretta. ‘Some will want to try keep things the same. Others will value the natural system more than the resources that we can get from it. Other people might say, hang on a minute, providing people with food is the most important thing.’

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The EAC is just one of many sleeping serpents stirred up by our warming world, a friendly force made unfamiliar. When we talk about climate change, this is its face. The carbon dioxide we have released into our skies traps energy in the earth’s system, and that energy is transmitted into winds and currents, benevolent climate beasts made hot and bothered, tipping chains of events that science struggles to measure, let alone forecast. Yet, already, they cast their restless shadows on our doorstep, our beaches, our plates.

‘The planet has been hotter, but it’s never changed this fast,’ says Gretta. ‘There’s never been a point in the past where the world looked like how it will in the future … there’s been nothing like it in terms of the combination of temperature, acidity, and other conditions … We’re going into a no-analogue future.’

 

 

Image: A 1685 map of ocean currents. Source: BBC.

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Jess Cockerill’s writing examines the links between culture and science.

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Comments

  1. As an amateur fisherperson my anecdotal experience in the lower part of Port Phillip would support that increased southern movement of fishes. As well as catching or finding tropical species previously unseen in Port Phillip, the large numbers of Kingfish now in the bay and around the Heads would support that southern migration which has steadily grown over the past decade. Whilst at Shark Bay WA recently I found a Japanese Fugu which I can only presume was brought south from equatorial climes by the Leeuwin current. Forecasting climate changes is akin to heralding the natural worlds unknown unknowns

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