Australia’s smallest fish among 22 at risk of extinction within two decades



Red-finned blue-eye
Bush Heritage Australia / Adam Kerezsy

Mark Lintermans, University of Canberra; Hayley Geyle, Charles Darwin University; Jaana Dielenberg, The University of Queensland; John Woinarski, Charles Darwin University; Stephen Beatty, Murdoch University, and Stephen Garnett, Charles Darwin University

The tragic fish kills in the lower Darling River drew attention to the plight of Australia’s freshwater fish, but they’ve been in trouble for a long time.

Many species have declined sharply in recent decades, and as many as 90 of Australia’s 315 freshwater fish species may now meet international criteria as threatened.




Read more:
We wrote the report for the minister on fish deaths in the lower Darling – here’s why it could happen again


No Australian fish species is yet listed officially as extinct, but some have almost certainly been lost before scientists even knew they existed. With so many species at risk, understanding which are in greatest peril is a vital first step in preventing extinctions.

This is what our new research has done. We’ve identified 20 freshwater fish species with a 50% or greater probability of extinction within the next two decades, and a further two with a 40-50% chance – unless there’s new targeted conservation action.

The Australian freshwater fishes at greatest risk of extinction.

Slipping through the conservation cracks

Many small-bodied species, including Australia’s smallest fish the red-finned blue-eye, look likely to be lost within a single human generation. These fish have evolved over millions of years.

Twelve of the species identified have only been formally described in the past decade, and seven are still awaiting description.

This highlights the urgent need to act before species are listed under the national legislation that gives fishes their conservation status, and even before they’re formally described.

These processes can take many years, at which point it may be too late for some species.

More than half the species on our list are galaxiids – small, scaleless fish, that live in cooler, upland streams and lakes. Trout, an introduced, predatory species, also favour these habitats, and the trout have taken a heavy toll on galaxiids and many other small species in southern Australia.

Shaw galaxias, a long light-brown fish.
Victoria’s Shaw galaxias – one of 14 galaxias species identified at high risk of extinction.
Tarmo Raadik

For example, the Victorian Shaw galaxias has been eaten out of much of its former range. Now just 80 individuals survive, protected by a waterfall from the trout below. We estimate the Shaw galaxias has an 80% chance or more of extinction within the next 20 years.




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Double trouble: this plucky little fish survived Black Summer, but there’s worse to come


Many galaxiids do not thrive or readily breed in captivity, so suitable trout-free streams are essential for their survival.

Improving trout management requires an urgent, sustained conservation effort, including collaborations with recreational fishers, increased awareness and changing values among government and key sectors of society.

Without this, trout will almost certainly cause many native galaxiids to go extinct.

Two researchers face a waterfall surounded by bushland.
This waterfall in NSW is all that protects the last population of stocky galaxias from the predatory trout below.
Mark Lintermans

Native fish out of their natural place can also be a problem. For example, sooty and khaki grunters – native fishing species people in northern Australia have widely moved – threatening the ancient Bloomfield River cod.

One disaster can lead to extinction

All of the most imperilled species are now highly localised, which means they’re restricted to very small areas. Their distributions range from only four to 44 square kilometres.

A single catastrophic event could completely wipe out these species, such as a large bushfire that fills their streams with ash and robs them of oxygen.

The SW Victoria River blackfish persists as three very small, isolated populations. The main threat to this species is recreational angling.
Tarmo Raadik

For example, until 2019 the Yalmy galaxias had survived in the cool creeks of the Snowy River National Park. But after the devastating Black Summer fires, just two individuals survived, one male and one female, in separate areas.

Millions of years of evolution could be lost if a planned reunion is too late.

One of the key steps to reduce this risk is moving fish to new safe locations so there are more populations. Researchers choose these new locations carefully to make sure they’re suitable for different species.

Climate change is another threat to all identified species, as it’s likely to reduce flows and water quality, or increase fires, storms and flooding. Many species have been forced to the edge of their range and a prolonged drought could dry their remaining habitat.

The short-tail galaxias existed in two small separated populations in creeks of the upper Tuross River Catchment, in the south coast of NSW. One stream dried in the recent drought, and the other was burnt in the subsequent fires.

Luckily the species is still hanging on in the burnt catchment, but only a single individual has been found in the drought-affected creek.

Rainbowfish swim among reeds
The main threat to the Daintree rainbowfish is loss of stream flow due to drought, climate change and water extraction.
Michael Hammer / Museum and Art Gallery of the Northern Territory, Author provided

Unlisted, unprotected

Our study is part of a larger project to identify plants and animals at high risk of extinction.

We found the extinction risks of the 22 freshwater fish species are much higher than those of the top 20 birds or mammals, yet receive far less conservation effort.

Only three of the highly imperilled fish species are currently listed as threatened under national environmental legislation: the red-finned blue-eye, Swan galaxias and little pygmy perch.

Listing species is vital to provide protection to survivors and can prompt recovery action. Given our research, 19 fish species should urgently be added to the national threatened species list, but conservation action should start now.

The little pygmy perch in the far south-west corner of WA is one of only three of the 22 imperilled species identified that’s formally protected under Australian laws.
Stephen Beatty/Harry Butler Institute, Murdoch University

Small native freshwater fishes are worth saving. They play a vital role in our aquatic ecosystems, such as predating on pest insect larvae, and are part of our natural heritage.

By identifying and drawing attention to their plight, we are aiming to change their fates. We cannot continue with business as usual if we want to prevent their extinctions.The Conversation

Mark Lintermans, Associate professor, University of Canberra; Hayley Geyle, Research Assistant, Charles Darwin University; Jaana Dielenberg, Science Communication Manager, The University of Queensland; John Woinarski, Professor (conservation biology), Charles Darwin University; Stephen Beatty, Research Leader (Catchments to Coast), Centre for Sustainable Aquatic Ecosystems, Harry Butler Institute, Murdoch University, and Stephen Garnett, Professor of Conservation and Sustainable Livelihoods, Charles Darwin University

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

Double trouble: this plucky little fish survived Black Summer, but there’s worse to come



Tarmo A. Raadik

Mark Lintermans, University of Canberra

This article is part of Flora, Fauna, Fire, a special project by The Conversation that tracks the recovery of Australia’s native plants and animals after last summer’s bushfire tragedy. Explore the project here and read more articles here.


On a coastal holiday last summer, I was preoccupied. Bushfires were tearing through southeast Australia, and one in particular had me worried. Online maps showed it moving towards the last remaining population of a plucky little fish, the stocky galaxias.

I’ve worked in threatened fish conservation and management for more than 35 years, but this species is special to me.

The stocky galaxias was formally described as a new species in 2014. Its only known population lives in a short stretch of stream in Kosciuszko National Park in New South Wales. A single event could wipe them out.

On January 2 the bushfires forced my family and I to evacuate our holiday home. As we returned to Canberra, I was still worried. Fire maps showed the stocky’s stream virtually surrounded by fire.

A few days later, I prepared for an emergency rescue.

Fire tore through south east Australia in January, threatening the stocky galaxias.
Victorian government

In critical danger

The stocky galaxias is the monarch of its small stream; the only fish species present. I’ve been trying to protect the stocky galaxias before it was even formally recognised.

Over the last century or more, the species has seen off threats from predatory trout, storms, droughts and bushfires. Snowy 2.0 is the latest danger.

It’s listed as critically endangered in NSW and is being assessed for a federal threatened listing. Before the fires, there were probably no more than 1,000-2,000 adults left in the wild.




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As the fires burned, I knew we had to move quickly. I wanted to collect up to 200 stocky galaxias and take them away for safekeeping.

Rainfall after bushfires is major threat to fish, because it washes ash and sediment into streams. Storms were forecast for the afternoon of January 15. So early that morning, myself and two colleagues, escorted by two staff from the NSW National Parks and Wildlife Service, drove to the stocky galaxias stream.

A colleague and I waded in and began electrofishing. This involved passing an electrical current through water, stunning fish momentarily so we could catch them.

The author and his colleagues used electrofishing to catch the fish.
Mark Lintermans

After 45 minutes we’d collected 68 healthy stocky galaxias. Woohoo! Further downstream we collected 74 more. By now, fire burned along the stream edge. We packed the fish into drums in the back of my car and drove out.

We headed to the NSW Department of Primary Industries’ trout hatchery at Jindabyne, where we measured each fish and took a genetic sample. I felt immensely relieved and satisfied that we’d potentially saved a species from extinction.

The fish have been thriving in the hatchery building. Stocky galaxias have never been kept in captivity before, but our years of field work told us the temperatures they encountered in the wild, so holding tanks could be set up appropriately.




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Back to the stream

The captive fish can be used for breeding, but the species has never been captive-bred before and this is not a trivial task.

When they’re reintroduced to the wild, the sites must be free of trout, and other invasive fish like climbing galaxias. Natural or artificial barriers should be in place to prevent invasive fish invasion.

In late March I finally got back to the stocky galaxias’ stream to see whether they’d survived. At the lower stretch of its habitat, the fire was not severe and the stream habitat looked good, with only a small amount of ash and sediment.

Upstream, the fire had been more severe. At the edge of the stream, heath was razed and patches of sphagnum moss were burnt. Again, sediment in the stream was not too abundant. But fish numbers were lower than normal, suggesting some there had not survived.

Stocky Galaxias live in a short stretch of a single stream.
Credit to come

The fight’s not over

The stocky galaxias species might have survived yet another peril, but the battle isn’t over.

Feral horse numbers in Kosciuszko National Park have increased dramatically in the last decade. They’ve degraded the banks of the stocky galaxias’ stream, making it wider and shallower and filling sections with fine sediment. This smothers the fish’s food resources, spawning sites and eggs.

Before the fires, plans were already afoot to fence off much of the stocky galaxias habitat to keep horses out. Fire damage to the park has delayed construction until early 2021.




Read more:
Snowy 2.0 threatens to pollute our rivers and wipe out native fish


The biggest long-term threat to the species is the Snowy 2.0 pumped hydro development. It threatens to transfer an invasive native fish, the climbing galaxias, to within reach of stocky galaxias habitat. There, it would compete for food with, and prey on, stocky galaxias – probably pushing it into extinction.

Despite this risk, in May this year the NSW government approved the Snowy 2.0 expansion, with approval conditions that I believe fail to adequately protect the stocky galaxias population. The project has also received federal approval.

Future in the balance

The stocky galaxias is unique and irreplaceable. I want my grandchildren to be able to show their grandchildren this little Aussie battler thriving in the wild.

The damage wrought by Snowy 2.0 may not be apparent for several decades. By then many politicians and bureaucrats now deciding the future of the stocky galaxias will be gone, as will I.

But 2020 will go down in history as the year the species was saved from fire, then condemned to possible extinction.

The Conversation

Mark Lintermans, Associate professor, University of Canberra

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

Don’t count your fish before they hatch: experts react to plans to release 2 million fish into the Murray Darling



Dean Lewins/AAP

Lee Baumgartner, Charles Sturt University; Jamin Forbes, Charles Sturt University, and Katie Doyle, Charles Sturt University

The New South Wales government plans to release two million native fish into rivers of the Murray-Darling Basin, in the largest breeding program of its kind in the state. But as the river system recovers from a string of mass fish deaths, caution is needed.

Having suitable breeding fish does not always guarantee millions of healthy offspring for restocking. And even if millions of young fish are released into the wild, increased fish populations in the long term are not assured.

For stocking to be successful, fish must be released into good quality water, with suitable habitat and lots of food. But these conditions have been quite rare in Murray Darling rivers over the past three years.

We research the impact of human activity on fish and aquatic systems and have studied many Australian fish restocking programs. So let’s take a closer look at the NSW government’s plans.

A mass fish kill at Menindee in northern NSW in January 2019 depleted Fisk stocks.
AAP

Success stories

According to the Sydney Morning Herald, the NSW restocking program involves releasing juvenile Murray cod, golden perch and silver perch into the Darling River downstream of Brewarrina, in northwestern NSW.

Other areas including the Lachlan, Murrumbidgee, Macquarie and Murray Rivers will reportedly also be restocked. These species and regions were among the hardest hit by recent fish kills.

Fish restocking is used worldwide to boost species after events such as fish kills, help threatened species recover, and increase populations of recreational fishing species.

Since the 1970s in the Murray-Darling river system, millions of fish have been bred in government and private hatcheries in spring each year. Young fish, called fingerlings, are usually released in the following summer and autumn.




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There have been success stories. For example, the endangered trout cod was restocked into the Ovens and Murrumbidgee Rivers between 1997 and 2006. Prior to the restocking program, the species was locally extinct. It’s now re-established in the Murrumbidgee River and no longer requires stocking to maintain the population.

In response to fish kills in 2010, the Edward-Wakool river system was restocked to help fish recover when natural spawning was expected to be low. And the threatened Murray hardyhead is now increasing in numbers thanks to a successful stocking program in the Lower Darling.

After recent fish kills in the Murray Darling, breeding fish known as “broodstock” were rescued from the river and taken to government and private hatcheries. Eventually, it was expected the rescued fish and their offspring would restock the rivers.

A Murray hardyhead after environment agencies transplanted a population of the endangered native fish.
North Central Catchment Management Authority

Words of caution

Fish hatchery managers rarely count their fish before they hatch. It’s quite a challenge to ensure adult fish develop viable eggs that are then fertilised at high rates.

Once hatched, larvae must be transported to ponds containing the right amount of plankton for food. The larvae must then avoid predatory birds, be kept free from disease, and grow at the right temperatures.




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When it comes to releasing the fish into the wild, careful decisions must be made about how many fish to release, where and when. Factors such as water temperature, pH and dissolved oxygen levels must be carefully assessed.

Introducing hatchery-reared fish into the wild does not always deliver dramatic improvements in fish numbers. Poor water quality, lack of food and slow adaptation to the wild can reduce survival rates.

In some parts of the Murray-Darling, restocking is likely to have slowed the decline in native fish numbers, although it has not stopped it altogether.

Address the root cause

Fish stocking decisions are sometimes motivated by economic reasons, such as boosting species sought by anglers who pay licence fees and support tourist industries. But stocking programs must also consider the underlying reasons for declining fish populations.

Swan Hill, home to a larger-than-life replica of the Murray cod, is just one river community that relies on anglers for tourism.
Flickr

Aside from poor water quality, fish in the Murray Darling are threatened by being sucked into irrigation systems, cold water pollution from dams, dams and weirs blocking migration paths and invasive fish species. These factors must be addressed alongside restocking.

Fish should not be released into areas with unsuitable habitat or water quality. The Darling River fish kills were caused by low oxygen levels, associated with drought and water extraction. These conditions could rapidly return if we have another hot, dry summer.

Stocking rivers with young fish is only one step. They must then grow to adults and successfully breed. So the restocking program must consider the entire fish life cycle, and be coupled with good river management.

The Murray Darling Basin Authority’s Native Fish Recovery Strategy includes management actions such as improving fish passage, delivering environmental flows, improving habitat, controlling invasive species and fish harvest restrictions. Funding the strategy’s implementation is a key next step.

Looking ahead

After recent rains, parts of the Murray Darling river system are now flowing for the first time in years. But some locals say the flows are only a trickle and more rain is urgently needed.

Higher than average rainfall is predicted between July and September. This will be needed for restocked fish to thrive. If the rain does not arrive, and other measures are not taken to improve the system’s health, then the restocking plans may be futile.




Read more:
We wrote the report for the minister on fish deaths in the lower Darling – here’s why it could happen again


The Conversation


Lee Baumgartner, Professor of Fisheries and River Management, Institute for Land, Water, and Society, Charles Sturt University; Jamin Forbes, Freshwater Ecologist, Charles Sturt University, and Katie Doyle, Freshwater Ecologist, Charles Sturt University

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

NSW has approved Snowy 2.0. Here are six reasons why that’s a bad move



Lucas Coch/AAP

Bruce Mountain, Victoria University and Mark Lintermans, University of Canberra

The controversial Snowy 2.0 project has mounted a major hurdle after the New South Wales government today announced approval for its main works.

The pumped hydro venture in southern NSW will pump water uphill into dams and release it when electricity demand is high. The federal government says it will act as a giant battery, backing up intermittent energy from by wind and solar.

We and others have criticised the project on several grounds. Here are six reasons we think Snowy 2.0 should be shelved.

1. It’s really expensive

The federal government announced the Snowy 2.0 project without a market assessment, cost-benefit analysis or indeed even a feasibility study.

When former Prime Minister Malcolm Turnbull unveiled the Snowy expansion in March 2017, he said it would cost A$2 billion and be commissioned by 2021. This was revised upwards several times and in April last year, Snowy Hydro awarded a A$5.1 billion contract for partial construction.

Snowy Hydro has not costed the transmission upgrades on which the project depends. TransGrid, owner of the grid in NSW, has identified options including extensions to Sydney with indicative costs up to A$1.9 billion. Massive extensions south, to Melbourne, will also be required but this has not been costed.

The Tumut 3 scheme, with which Snowy 2.0 will share a dam.
Snowy Hydro Ltd

2. It will increase greenhouse gas emissions

Both Snowy Hydro Ltd and its owner, the federal government, say the project will help expand renewable electricity generation. But it won’t work that way. For at least the next couple of decades, analysis suggests Snowy 2.0 will store coal-fired electricity, not renewable electricity.

Snowy Hydro says it will pump the water when a lot of wind and solar energy is being produced (and therefore when wholesale electricity prices are low).




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Snowy 2.0 is a wolf in sheep’s clothing – it will push carbon emissions up, not down


But wind and solar farms produce electricity whenever the resource is available. This will happen irrespective of whether Snowy 2.0 is producing or consuming energy.

When Snowy 2.0 pumps water uphill to its upper reservoir, it adds to demand on the electricity system. For the next couple of decades at least, coal-fired electricity generators – the next cheapest form of electricity after renewables – will provide Snowy 2.0’s power. Snowy Hydro has denied these claims.

Khancoban Dam, part of the soon-to-be expanded Snowy Hydro scheme.
Snowy Hydro Ltd

3. It will deliver a fraction of the energy benefits promised

Snowy 2.0 is supposed to store renewable energy for when it is needed. Snowy Hydro says the project could generate electricity at its full 2,000 megawatt capacity for 175 hours – or about a week.

But the maximum additional pumped hydro capacity Snowy 2.0 can create, in theory, is less than half this. The reasons are technical, and you can read more here.

It comes down to a) the amount of time and electricity required to replenish the dam at the top of the system, and b) the fact that for Snowy 2.0 to operate at full capacity, dams used by the existing hydro project will have to be emptied. This will result in “lost” water and by extension, lost electricity production.



The Conversation, CC BY-ND

4. Native fish may be pushed to extinction

Snowy 2.0 involves building a giant tunnel to connect two water storages – the Tantangara and Talbingo reservoirs. By extension, the project will also connect the rivers and creeks connected to these reservoirs.

A small, critically endangered native fish, the stocky galaxias, lives in a creek upstream of Tantangara. This is the last known population of the species.

The stocky galaxias.
Hugh Allan

An invasive native fish, the climbing galaxias, lives in the Talbingo reservoir. Water pumped from Talbingo will likely transfer this fish to Tantangara.

From here, the climbing galaxias’ capacity to climb wet vertical surfaces would enable it to reach upstream creeks and compete for food with, and prey on, stocky galaxias – probably pushing it into extinction.

Snowy 2.0 is also likely to spread two other problematic species – redfin perch and eastern gambusia – through the headwaters of the Murrumbidgee, Snowy and Murray rivers.




Read more:
Snowy 2.0 threatens to pollute our rivers and wipe out native fish


5. It’s a pollution risk

Snowy Hydro says its environmental impact statement addresses fish transfer impacts, and potentially serious water quality issues.

Four million tonnes of rock excavated to build Snowy 2.0 would be dumped into the two reservoirs. The rock will contain potential acid-forming minerals and other harmful substances, which threaten to pollute water storages and rivers downstream.

When the first stage of the Snowy Hydro project was built, comparable rocks were dumped in the Tooma River catchment. Research in 2006 suggested the dump was associated with eradication of almost all fish from the Tooma River downstream after rainfall.

Snowy 2.0 threatens to pollute pristine Snowy Mountains rivers.
Schopier/Wikimedia

6. Other options were not explored

Many competing alternatives can provide storage far more flexibly for a fraction of Snowy 2.0’s price tag. These alternatives would also have far fewer environmental impacts or development risks, in most cases none of the transmission costs and all could be built much more quickly.

Expert analysis in 2017 identified 22,000 potential pumped hydro energy storage sites across Australia.

Other alternatives include chemical batteries, encouraging demand to follow supply, gas or diesel generators, and re-orienting more solar capacity to capture the sun from the east or west, not just mainly the north.

Where to now?

The federal government, which owns Snowy Hydro, is yet to approve the main works.

Given the many objections to the project and how much has changed since it was proposed, we strongly believe it should be put on hold, and scrutinised by independent experts. There’s too much at stake to get this wrong.




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Five gifs that explain how pumped hydro actually works


The Conversation


Bruce Mountain, Director, Victoria Energy Policy Centre, Victoria University and Mark Lintermans, Associate professor, University of Canberra

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

Dinner to die for: how fish use their spines to fend off hungry seals


Vincent Antony, Author provided

David Hocking, Monash University; Felix Georg Marx, Te Papa Tongarewa; Silke Cleuren, Monash University, and William Parker, Monash University

What price are you willing to pay for food?

For most of us, that’s a question about money. But what if the cost were actual pain, injury and death? For some seals and dolphins, this a real risk when hunting.

We took a close look at a New Zealand (or long-nosed) fur seal that stranded at Cape Conran in southeastern Australia, and discovered it had numerous severe facial injuries. These wounds were all caused by fish spines, and they show the high price these animals are willing to pay in pursuit of a meal.




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Victim or perpetrator?

When the unfortunate seal was first spotted dead on the beach, it was clear something was amiss: the animal was emaciated, and had a large fish spine stuck in its cheek.

Location where the seal was found in south-eastern Australia.
David Hocking

A team of scientists from the Department of Environment, Land, Water and Planning (DELWP), Museums Victoria and Monash University decided to investigate, and took a CT scan of the seal’s head. The results were striking: fish spines had penetrated not just both cheeks, but also the nose and jaw muscles.

On closer examination, we also found ten stab wounds, likely from further fish spines that had been pulled out. The wounds were spread all over the face and throat, and at least some appear to have festered. They may have made feeding difficult, and ultimately may have caused the animal to starve.

These wounds were likely not the result of unprovoked attacks. They were probably inflicted by prey that simply did not want to be eaten.

3D computer models of the seal’s skull showing the position of the stingray barbs and ghostshark spines.
David Hocking

How to fight off a hungry seal … or at least teach it a lesson

Many fish species have evolved elaborate defence systems against predators, such as venomous spines that can inflict painful wounds.

Our seal appears to have been done in by two species of cartilaginous fish. One was the elusive Australian ghostshark (also known as elephant fish), a distant relative of true sharks that has a large serrated spine on its back.

The other was a stingaree: a type of small stingray with a venomous tail barb that can be whipped around like a scorpion’s tail. Its sting is normally aimed at would-be predators, but sometimes also catches the feet of unwary humans.

Deadly prey: the Australian ghostshark and stingaree, both armed with sharp venomous spines.
David Hocking
Sharp harpoon-like barb from the tail of a stingaree that was found embedded within the face of an unlucky New Zealand fur seal.
David Hocking, CC BY-SA

How to eat a spiky fish

Until recently, most of what we knew about the diet New Zealand fur seals was based on bony remains left in their poo. This technique largely overlooks cartilaginous fish, whose skeletons are made of cartilage instead of bone. As a result, we didn’t realise fur seals target these creatures.

New studies of the DNA of devoured prey in the seals’ scats now suggest they commonly feed on ghostsharks. Stingarees and other rays are less common, but evidently still form part of their diet. So how do the seals handle such dangerous prey on a regular basis?

It all comes down to table manners. Ghostsharks and rays are too large to be swallowed whole, and hence must be broken into smaller chunks first. Fur seals achieve this by violently shaking their prey at the water’s surface, largely because their flippers are no longer capable of grasping and tearing.

Fur seals can eat small fish whole, but need to tear large prey into edible chunks.

Shaking a fish in the right way (for example by gripping it at the soft belly) may allow seals to kill and consume it without getting impaled. Nevertheless, some risk remains, whether because of struggling prey, poor technique, or simply bad luck. The wounds on our seal’s cheeks suggest that it may accidentally have slapped itself with a ghostshark spine while trying to tear it apart.

Australian ghostshark being eaten by an Australian fur seal belly first, thus avoiding the sharp spine on its back.
Photo by Vincent Antony
Australian ghostshark being eaten by an Australian fur seal belly first, thus avoiding the sharp spine on its back.
Photo by Vincent Antony

Fish spines – a common problem?

One of the challenges we face as scientists is knowing how to interpret isolated observations. Are fish spines a common problem for fur seals, or was our individual just particularly unlucky? We don’t know.

New techniques like analysing DNA from scats means that we are only just beginning to get a better idea of the full range of prey marine mammals target. Likewise, medical imaging techniques such as CT scanning are rarely applied to marine mammal strandings, and injuries like the ones in our seal may often go unnoticed.

CT scans of the jaws of a wedgefish (Rhynchobatus sp.) from Dean et al. (2017)
Dean et al. (2017)

Nevertheless, fish spine injuries have been observed in other ocean predators, including dolphins, killer whales, and rays. One wedgefish described in another recent study had as many as 62 spines embedded in its jaw! Now that we know what to look for, we may finally get a better idea of how common such injuries really are.

For now, this extraordinary example vividly demonstrates the choices and dangers wild animals face as they try to make a living. For our seal, the seafood ultimately won, but we will never know if the fish that killed it got away, or if the wounds they left are evidence of the seal’s last meal.




Read more:
When mammals took to water they needed a few tricks to eat their underwater prey


The Conversation


David Hocking, Postdoctoral fellow, Monash University; Felix Georg Marx, Curator Vertebrates, Te Papa Tongarewa; Silke Cleuren, PhD candidate, Monash University, and William Parker, PhD Candidate, Monash University

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

Snowy 2.0 threatens to pollute our rivers and wipe out native fish



Schopier/Wikimedia

John Harris, UNSW and Mark Lintermans, University of Canberra

The federal government’s Snowy 2.0 energy venture is controversial for many reasons, but one has largely escaped public attention. The project threatens to devastate aquatic life by introducing predators and polluting important rivers. It may even push one fish species to extinction.

The environmental impact statement for the taxpayer-funded project is almost 10,000 pages long. Yet it fails to resolve critical problems, and in one case seeks legal exemptions to enable Snowy 2.0 to wreak environmental damage.

The New South Wales government is soon expected to grant the project environmental approval. This process should be suspended, and independent experts should urgently review the project’s environmental credentials.

Native fish extinctions

Snowy Hydro Limited, a Commonwealth-owned corporation, is behind the Snowy 2.0 project in the Kosciuszko National Park in southern NSW. It involves building a giant tunnel to connect two water storages – the Tantangara and Talbingo reservoirs. By extension, the project will also connect the rivers and creeks connected to these reservoirs.

A small, critically endangered native fish, the stocky galaxias, lives in a creek upstream of Tantangara. This is the last known population of the species.




Read more:
Snowy 2.0 is a wolf in sheep’s clothing – it will push carbon emissions up, not down


An invasive native fish, the climbing galaxias, lives in the Talbingo reservoir (it was introduced from coastal streams when the original Snowy project was built). Water pumped from Talbingo will likely transfer this fish to Tantangara.

From here, the climbing galaxias’ capacity to climb wet vertical surfaces would enable it to reach upstream creeks and compete for food with, and prey on, stocky galaxias – probably pushing it into extinction.

The stocky galaxias.
Hugh Allan

Snowy Hydro has applied for an exemption under NSW biosecurity legislation to permit the transfer of the climbing galaxias and two other fish species: the alien, noxious redfin perch and eastern gambusia.

Redfin perch compete for food with other species and produce many offspring. They are voracious, carnivorous predators, known to prey on smaller fish.

Redfin perch also allow the establishment of a fatal fish disease – epizootic haematopoietic necrosis virus – or EHN. This disease kills the endangered native Macquarie perch, the population of which below Tantangara is one of very few remaining.

If Snowy 2.0 is granted approval, it is likely to spread these problematic species through the headwaters of the Murrumbidgee, Snowy and Murray rivers.

The climbing galaxias, which threatens the native stocky galaxias.
Stella McQueen/Wikimedia

Acid and asbestos pollution

Four million tonnes of rock excavated to build Snowy 2.0 would be dumped into the two reservoirs. Snowy Hydro has not assessed the pollution risks this creates. The rock will contain potential acid-forming minerals and a form of asbestos, which threaten to pollute water storages and rivers downstream.

When the first stage of the Snowy Hydro project was built, comparable rocks were dumped in the Tooma River catchment. Research in 2006 suggested the dump was associated with eradication of almost all fish from the Tooma River downstream after rainfall.




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Addressing the problems

The environmental impact statement either ignores, or pays inadequate attention to, these environmental problems.

For example, installing large-scale screens at water inlets would be the best way to prevent fish transfer from Talbingo Dam, but Snowy Hydro has dismissed it as too costly.

Snowy Hydro instead proposes a dubious second-rate measure: screens to filter pumped flows leaving Tantangara reservoir, and building a barrier in the stream below the stocky galaxias habitat.

The best and cheapest way to prevent damage from alien species is stopping the populations from establishing. Trying to control or eradicate pest species once they’re established is far more difficult and costly.



The Conversation, CC BY-ND

We believe the measures proposed by Snowy Hydro are impractical. It would be very difficult to maintain a screen fine and large enough to prevent fish eggs and larvae moving out of Tantangara reservoir and such screens would be totally ineffective at preventing the spread of EHN virus.

A six metre-high waterfall downstream of the stocky galaxias habitat currently protects the critically endangered species from other invasive species threats. But climbing galaxias have an extraordinary ability to ascend wet surfaces. They would easily climb the waterfall, and possibly the proposed creek barrier as well.

Such an engineered barrier has never been constructed in Australia. We are informed that in New Zealand, the barriers have not been fully effective and often require design adjustments.




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Even if the barrier protected the stocky galaxias at this location, efforts to establish populations in other unprotected regional streams would be severely hampered by the spread of climbing galaxias.

Preventing redfin and EHN from entering the Murrumbidgee River downstream of Tantangara depends on the reservoir never spilling. The reservoir has spilled twice since construction in the 1960s, and would operate at much higher water levels when Snowy 2.0 was operating. Despite this, Snowy Hydro says it has “high confidence in being able to avoid spill”.

If dumped spoil pollutes the two reservoirs and Murrumbidgee and Tumut rivers, this would also have potentially profound ecological impacts. These have not been critically assessed, nor effective prevention methods identified.

The Tumut 3 scheme, part of the existing Snowy Hydro scheme.
Snowy Hydro Ltd

Looking to the future

Snowy 2.0 will likely make one critically endangered species extinct and threaten an important remaining population of another, as well as pollute freshwater habitats. As others have noted, the project is also questionable on other environmental and economic grounds.

These potential failures underscore the need to immediately halt Snowy 2.0, and subject it to independent expert scrutiny.


In response to the issues raised in this article, a spokesperson for Snowy Hydro said:

“Snowy Hydro’s EIS, supported by numerous reports from independent scientific experts, extensively address potential water quality and fish transfer impacts and the risk mitigation measures to be put in place. As the EIS is currently being assessed by the NSW Government we have no further comment.”


A previous version of this article incorrectly stated that water pumped from Tantangara will likely transfer fish to Talbingo. It should have said water pumped from Talbingo will likely transfer fish to Tantangara.The Conversation

John Harris, Adjunct Associate Professor, Centre for Ecosystem Science, UNSW and Mark Lintermans, Associate professor, University of Canberra

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

I studied what happens to reef fish after coral bleaching. What I saw still makes me nauseous



Victor Huertas, Author provided

Jodie L. Rummer, James Cook University

The Great Barrier Reef is suffering its third mass bleaching event in five years. It follows the record-breaking mass bleaching event in 2016 that killed a third of Great Barrier Reef corals, immediately followed by another in 2017.

While we don’t know if fish populations declined from the 2016 bleaching disaster, one 2018 study did show the types of fish species on some coral reefs changed. Our study dug deeper into fish DNA.

I was part of an international team of scientists that, for the first time, tracked wild populations of five species of coral reef fish before, during, and after the 2016 marine heatwave.

From a scientific perspective, the results are fascinating and world-first.

Marine heatwaves are now becoming more frequent and more severe with climate change. Corals are bleaching, as pictured here.
Jodie Rummer, Author provided

We used gene expression as a tool to survey how well fish can handle hotter waters. Gene expression is the process where a gene is read by cell machinery and creates a product such as a protein, resulting in a physical trait.

We know many tropical coral reef fish are already living at temperatures close to their upper limits. Our findings can help predict which of these species will be most at risk from repeated heatwaves.




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But from a personal perspective, I still feel nauseous thinking about what the reef looked like during this project. I’ll probably feel this way for a long time.

Rewind to November 2015

We were prepared. Back then we didn’t know the reef was about to bleach and lead to widespread ecological devastation. But we did anticipate that 2016 would be an El Niño year. This is a natural climate cycle that would mean warm summer waters in early 2016 would stick around longer than usual.

But we can’t blame El Niño – the ocean has already warmed by 1°C above pre-industrial levels from continued greenhouse gas emissions. What’s more, marine heatwaves are becoming more frequent and severe with climate change.

Given this foresight, we took some quick liver biopsies from several coral reef fish species at our field site in December 2015, just in case.

Coral bleaching at Magnetic Island, March 2020.
Victor Huertas, Author provided

A couple months later, we were literally in hot water

In February 2016, my colleague and I were based on Lizard Island in the northern part of the Great Barrier Reef working on another project.

The low tides had shifted to the afternoon hours. We were collecting fish in the shallow lagoon off the research station, and our dive computers read that the water temperature was 33°C.




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We looked at each other. These are the temperatures we use to simulate climate change in our laboratory studies for the year 2050 or 2100, but they’re happening now.

Over the following week, we watched corals turn fluorescent and then bone-white.

The water was murky with slime from the corals’ immune responses and because they were slowly exuding their symbiotic zooxanthellae – the algae that provides corals with food and the vibrant colours we know and love when we think about a coral reef. The reef was literally dying before our eyes.

A third of the corals on the Great Barrier Reef perished after the 2016 heatwave.
Jodie Rummer, Author provided

Traits for dealing with heatwaves

We sampled fish during four time periods around this devastating event: before, at the start, during, and after.

Some genes are always “switched on”, regardless of environmental conditions. Other genes switch on or off as needed, depending on the environment.

If we found these fish couldn’t regulate their gene expression in response to temperature stress, then the functions – such as metabolism, respiration, and immune function – also cannot change as needed. Over time, this could compromise survival.




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The plasticity (a bit like flexibility) of these functions, or phenotypes, is what buffers an organism from environmental change. And right now, this may be the only hope for maintaining the health of coral reef ecosystems in the face of repeated heatwave events.

So, what were the fish doing?

We looked at expression patterns of thousands of genes. We found the same genes responded differently between species. In other words, some fish struggled more than others to cope with marine heatwaves.

Ostorhinchus doederleini, a species of cardinalfish, is bad at coping with marine heatwaves.
Göran Nilsson, Author provided

The species that coped the least was a nocturnal cardinalfish species (Cheilodipterus quinquelineatus). We found it had the lowest number of differentially expressed genes (genes that can switch on or off to handle different stressors), even when facing the substantial change in conditions from the hottest to the coolest months.

In contrast, the spiny damselfish (Acanthochromis polyacanthus) responded to the warmer conditions with changes in the expression of thousands of genes, suggesting it was making the most changes to cope with the heatwave conditions.

What can these data tell us?

Our findings not only have implications for specific fish species, but for the whole ecosystem. So policymakers and the fishing industry should screen more species to predict which will be sensitive and which will tolerate warming waters and heatwaves. This is not a “one size fits all” situation.

One of the species that showed the least amount of change under warming was Cheilodipterus quinquelineatus.
Moises Antonio Bernal de Leon, Author provided

Fish have been on the planet for more than 400 million years. Over time , they may adapt to rising temperatures or migrate to cooler waters.

But, the three recent mass bleaching events is unprecedented in human history, and fish won’t have time to adapt.




Read more:
Attention United Nations: don’t be fooled by Australia’s latest report on the Great Barrier Reef


My drive to protect the oceans began when I was a child. Now it’s my career. Despite the progress my colleagues and I have made, my nauseous feelings remain, knowing our science alone may not be enough to save the reef.

The future of the planet, the oceans, and the Great Barrier Reef lies in our collective actions to reduce global warming. What we do today will determine what the Great Barrier Reef looks like tomorrow.The Conversation

Jodie L. Rummer, Associate Professor & Principal Research Fellow, James Cook University

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

Sure, save furry animals after the bushfires – but our river creatures are suffering too


Jamie Pittock, Australian National University

The hellish summer of bushfires in southeast Australia triggered global concern for our iconic mammals. Donations flooded in from at home and around the world to help protect furry species.

But there’s a risk the government and public responses will not see the fish for the koalas.

Of the 113 priority fauna species identified by the federal government as worst impacted by bushfires, 61 (54%) are freshwater species that live in or around our inland rivers, such as fish, frogs, turtles and the iconic platypus.

These animals and ecosystems were already struggling due to prolonged drought and mismanagement of the Murray Darling Basin. Saving koalas and other mammals is of course important, but freshwater species should also be a priority for post-fire environmental programs.

A picture of devastation

The government’s priority species list includes three turtle species, 17 frogs, 22 crayfish, 17 fish and the platypus. Rounding out the list is an alpine stonefly, although many other invertebrates are also likely to be affected (as well as other species that depend on moist, streamside forest habitats).

Excluding tropical savannah, the recent bushfires burnt more than 7.7 million hectares in Victoria, South Australia, New South Wales, Queensland and Western Australia. Rainforests and riparian (riverside) forests were extensively damaged along the Australian east coast and alps. These are normally moist environments, which are not adapted to fire.

Plant and animal species at the edge of waterways, in peat wetlands and in riverside forests are likely to have been burnt or killed by heat, such as crustaceans , lizards, and corroboree and mountain frogs in the alps and east coast rainforests.




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Burnt riverside forests no longer shade the water, making water temperatures hotter and leading to increased evaporation that may stress surviving wildlife. The loss of vegetation cover also leaves prey exposed to predators.

Following recent rain, water flowing into rivers has washed ash into streams. This clogs fish gills and brings nutrients that drive algal blooms. Sediment washed into waterways fills in the gaps between rocks and holes in river beds – places where many species shelter and breed. For instance, the River Murray catchment’s last population of Macquarie perch was impacted as rain washed ash and sediment into Mannus Creek in southern NSW.

Fires tend to burn forests in patches, sometimes leaving refuges for land-based animals. However fire damage to waterways flows downstream, systematically degrading the habitat of aquatic animals by leaving little clean water to hide in.

Bushfire silt clogging the usually pristine Tambo river in the Victorian high country in January.
David Crosling/AAP

Long-term damage

The devastating impact of the fires in river environments may be long-lived.

When aquatic animals species are wiped out in particular rivers, they may not be able to recolonise from surviving populations in other unconnected rivers.

Some species will invariably now be closer to extinction. For example many key peat swamp habitats of the critically endangered northern corroboree frog have been burnt in the Bogong Peaks and Brindabella mountains of NSW and the ACT.




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The sweet relief of rain after bushfires threatens disaster for our rivers


And after fires, fast-growing young eucalyptus forests transpire much more water than older burnt trees. This may reduce inflows into streams for a century.

The recent bushfires followed several years of extreme drought across much of Australia. In the Murray-Darling Basin, these challenges were compounded by poor water management that contributed to dried-up rivers and mass fish deaths.

Water-sharing rules in the basin determine how much water is allocated to agriculture and the environment. Current water-sharing plans do not explicitly include allocations to manage losses due to climate change, and as the plans will only be updated once a decade, it is questionable whether they will be adjusted to sustain flows needed to conserve threatened species.

Much corroboree frog habitat was destroyed during the fires.
Melbourne Zoo

Here’s what to do

After the fires, government officials and scientists rescued a number of “insurance” populations of threatened aquatic animals such as turtle and fish species, and took them to captive breeding facilities, such as the stocky galaxias fish in the alps. We must ensure healthy habitat is available for these animals to re-establish viable populations when released.

In the short term, we must protect surviving and regenerating habitat. Government programs are off to a good start in promising to cull feral predators such as cats and foxes, as well as grazing animals such as pigs, deer and goats. The NSW and Victorian governments must also remove feral horses in the Australian Alps that are damaging the swamp habitats and streams.

Now so many infested riverside forests are accessible, it is a key time to control weed regrowth.




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Last summer’s fish carnage sparked public outrage. Here’s what has happened since


In the medium term, we should expand programs to fence livestock out of waterways, install other watering points for these animals and revegetate stream banks.

Deep holes in rivers and streams with cool water are important refuges for aquatic animals, and ways to restore them should be investigated.

Impediments to fish migration, such as weirs, should be removed or fish “ladders” installed to aid fish movement. Aquatic species often won’t breed unless the water is the right temperature in the right season; to prevent the release of overly cold water from the bottom of dams, better water release structures should be installed.

Years of drought meant rivers and aquatic life were already vulnerable before the fires.
Dean Lewins/AAP

An opportunity for change

Successive governments have been asleep at the tiller when it comes to threatened aquatic animals. Official recovery plans for many fire-affected species have not been adequately funded or implemented.

In the Murray-Darling Basin for example, a native fish strategy was shelved in 2013 after the NSW government reportedly pulled funding.

The impending release of a new fish strategy, and other post-fire recovery actions, are an opportunity for governments to right past wrongs and ensure our precious freshwater species thrive into the future.The Conversation

Jamie Pittock, Professor, Fenner School of Environment & Society, Australian National University

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

Last summer’s fish carnage sparked public outrage. Here’s what has happened since



Graeme McCrabb/AAP

Lee Baumgartner, Charles Sturt University and Max Finlayson, Charles Sturt University

As this summer draws to a close, it marks just over a year since successive fish death events at Menindee in Lower Darling River made global headlines.

Two independent investigations found high levels of blue-green algae and low oxygen levels in the water caused the deaths. Basically, the fish suffocated.




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The conditions were caused by a combination of water extraction and extremely dry conditions which effectively stopped the river from flowing. Both investigations concluded that until more water flowed in the Darling, in western New South Wales, further fish kills were very likely.

So what’s happened since, and does the recent rain mean the crisis won’t be repeated?

Federal and state government action

In April last year the federal government committed A$70 million to improve the river’s health and prevent more fish deaths. Let’s examine what’s been done so far:

– Native fish management and recovery strategy: Parts of a draft native fish management and recovery strategy have been released for public consultation. The plan has included governments, academics, the community and indigenous groups.

– Native fish hatchery: Government hatchery facilities at Narrandera in NSW will be upgraded to hold and breed more fish. But reintroducing fish into affected areas is challenging and could be a decades-long program.

– Research: The government committed to new research into hydrology and climate change. A panel has been formed and the oversight committee is scoping the most effective research outcomes to better manage water under a changed climate.

– Fish passage infrastructure: Fish ladders – structures that allow fish to travel around obstacles on a river – are needed at sites on the lower and upper Darling. Fish ladder concept designs have progressed and are also part of the NSW government’s Western Weirs project.

-In-stream cameras: Live-stream feeds of the Darling River are not yet available.

-Meter upgrades and water buybacks: Discussions have begun as part of a commitment to buy back A-class water licenses from farmers and return water to the rivers. Rollout of improved metering is due over the next five years.

Progress on these actions is welcome. But the investigation panels also recommended other actions to help fish populations recover over the long term, including ensuring fish habitat and good water quality.

Further fish deaths

In 2003, basin native fish communities were estimated to be at 10% of pre-European levels and the spates of fish deaths will have reduced this further.

Over spring and summer in 2019, conditions in the Darling River deteriorated. A series of smaller, but significant, fish deaths prompted government agencies and communities to conduct emergency “fish translocations”.. Aerators were deployed in a bid to improve the de-oxygenation. Fish were moved to more suitable water bodies, or to hatcheries to create insurance populations.

By spring, once-mighty rivers such as the Darling and Macquarie had dried to shallow pools. As summer progressed, more than 30 fish die-offs occurred in the Macquarie, Namoi, Severn, Mehi and Cudgegong rivers and Tenterfield Creek.

What about the rain?

Strong recent rainfall means upper parts of the Darling catchment are now flowing for the first time in more than two years. Flows are passing over the Brewarrina Weir and associated fishway.

A flowing Darling is great, but it raises questions over future water management. Farmers have been waiting for years for the Darling to flow and will be eager to extract water for agricultural productivity. Likewise, the environment has been awaiting a “flush” to reset the system and restore ecological productivity.




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After the rains, the NSW government allowed irrigators to harvest floodwaters to reduce the threat of damage to private infrastructure. Now that threat has subsided, governments are working together to “actively manage” the event – meaning water rules will be decided as the flow progresses, in consultation with water users and environmental managers.

But there is still significant debate on how best to manage water over the longer term.

Water use on the Darling River remains highly contested.
Dean Lewins/AAP

Is a flowing Darling a return to normal?

The current flows in the Darling are far from a return to normal conditions. NSW is still in drought, and the river flows are yet to reach the Lower Darling. Many children in the Menindee township have not seen a flowing Darling in their lifetime.

Indigenous elders and recreational fishers – those who remember when the river flowed freely and was full of fish – are lamenting the recent declines. In parts of the system, dry riverbeds and isolated pools are still begging to be connected so fish can move about, spawn, and naturally recover.




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River flows could take up to six weeks to reach the lower Darling, and follow-up rain is urgently needed to avoid another summer of fish carnage. Future water sharing strategies must protect both upstream and downstream communities. Some people are lobbying for the Menindee lakes to be listed as internationally important under the Ramsar Convention on Wetlands to ensure biodiversity and water management work together.

Undoing over 200 years of fish declines will require a sustained effort, with a significant investment in recovery actions over a long period. We must recognise Australia is a country of long droughts and flooding rains, and develop a proactive native fish strategy that reduces the probability of a similar disaster in future.

But unfortunately, as history has shown that when we transition from drought to flood, our memories can be short.The Conversation

Lee Baumgartner, Professor of Fisheries and River Management, Institute for Land, Water, and Society, Charles Sturt University and Max Finlayson, Adjunct Professor, Charles Sturt University

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

Fish larvae float across national borders, binding the world’s oceans in a single network


Larval black sea bass, an important commercial species along the US Atlantic coast.
NOAA Fisheries/Ehren Habeck

Nandini Ramesh, University of California, Berkeley; James Rising, London School of Economics and Political Science, and Kimberly Oremus, University of Delaware

Fish populations are declining around the world, and many countries are trying to conserve them by regulating their fishing industries. However, controlling fishing locally may not do enough to strengthen fish populations. Often one nation’s fish stocks depend on the spawning grounds of a neighboring country, where fish release eggs and sperm into the water and larvae hatch from fertilized eggs.

We do research on oceans, climate and fisheries. In a recent study, we showed that global fisheries are even more tightly connected than previously understood. The world’s coastal marine fisheries form a single network, thanks to the drift of larvae along ocean currents.

This suggests that country-by-country fishery management may be fundamentally insufficient. If a fish species that provides food to one country should decline, the amount of fish spawn, or eggs and larvae, riding the ocean currents from there to other countries would also decline dramatically, resulting in further loss of fish elsewhere.

Many countries live with this risk, although they may not realize it. To manage fisheries effectively, nations must understand where the fish in their territories originate.

Ocean currents affect the speed at which fish eggs and larvae drift and vary through the year. This map shows surface current speeds for January: yellow = fastest, dark blue = slowest. Each country’s territory is highlighted with red dots during the month of maximum spawning activity in that country. In each territory, a different number of species spawn in each month of the year. The red dots appear in the month during which the largest number of species spawn in that territory.

Crossing national borders

Fish don’t recognize political boundaries, and regularly travel internationally. Scientists have tracked adult fish movements using electronic tags, and have shown that a few species migrate over long distances.

Countries and territories have negotiated agreements to ensure sustainable sharing of migratory fish. One such agreement joins several nations in the Western and Central Pacific Fisheries Commission to ensure that the territories fish cross share them sustainably.

But fish eggs and larvae are much harder to follow. Many species lay eggs in large numbers that float near the ocean surface. When they hatch, larvae measure a few millimeters long and continue to drift as plankton until they grow large enough to swim. During these stages of the life cycle, ocean currents sweep fish spawn across international boundaries.

Simulating the journeys of eggs and larvae

Like weather on land, the pattern of ocean currents varies with the seasons and can be predicted. These currents are typically sluggish, traveling about an inch per second, or less than 0.1 miles per hour.

There are a few exceptions: Currents along the eastern coasts of continents, like the Gulf Stream in North America or the Kuroshio in Asia, and along the equator can be significantly faster, reaching speeds of 2 miles per hour. Even a gentle current of 0.1 miles per hour can carry spawn 40 miles over a month, and some species can float for several months.

Government and academic scientists use a vast network of satellites, moored instruments and floating buoys to monitor these surface flows. Using this information, we performed a computer simulation of where drifting particles would be carried over time. Scientists have used this type of simulation to study the spread of marine plastic pollution and predict where debris from plane crashes at sea could have washed ashore.

Different fish species spawn in different seasons, and a single species may spawn in several months at different locations. We matched the seasons and locations of spawning for over 700 species with ocean current data, and simulated where their spawn would drift. Then, using records of where those species have been fished, and information about how suitable conditions are for each species in different regions, we deduced what fraction of the fish caught in each country arrived from other countries because of ocean currents.

A small-world network

Scientists and policymakers can learn a lot by studying these international connections. Each species that floats across international boundaries during its plankton stage represents a linkage between countries. These linkages span the world in a dense, interconnected network.

Each color represents a region in the network of fish larvae connections. This map shows the strongest 467 connections among a total of 2,059 that the authors modeled.
Nandini Ramesh, James Rising and Kimberly Oremus, CC BY-ND

At a global level, this network of connections has an important property: It is a small-world network. Small-world networks connect regions that are far apart to each other by just a few steps along the network. The concept is rooted in social scientist Stanley Milgram’s 1960s experiments with social networks, which found that it was possible for a letter to reach almost any total stranger by passing through six or fewer hands. Milgram’s work was popularized in the 1990 play “Six Degrees of Separation.”

Among fisheries, the world seems even smaller: We found that the average number of degrees of separation among fisheries is five. This means that local problems can become global risks.

For example, imagine that a fishery collapses in the middle of the Mediterranean. If the population in one spawning region collapses, it could quickly put pressure on neighboring fisheries dependent upon it. If fishers in those neighboring countries overfish the remaining population or shift to other species, the disturbance can grow. Within just a few years, a fisheries disturbance could travel around the world.

We assessed how countries would be affected in terms of food security, employment and gross domestic product if they were to lose access to fish spawn from other territories. The most affected countries cluster in the Caribbean, the western Pacific, Northern Europe and West Africa. These hotspots correspond to the network’s most clustered areas, because the effects of these flows of fish spawn are most pronounced where many coastal countries lie in close proximity.

International flows of fish eggs and larvae affect countries’ total catch, food security, jobs and economies.
Nandini Ramesh, James Rising and Kimberly Oremus, CC BY-ND

Thinking globally about fisheries

Because the world’s fisheries are so interconnected, only international cooperation that takes flows of fish spawn into account can effectively manage them. Aside from egg and larvae connections, fisheries are linked by movements of adult fish and through agreements among countries allowing them to fish in each other’s waters.

All of this suggests that fishery management is best conducted at a large, international scale. Proposals for doing this include defining Large Marine Ecosystems to be jointly managed and creating networks of Marine Protected Areas that safeguard a variety of critical habitats. Ideas like these, and careful study of interdependence between national fisheries, are crucial to sustainable use of the oceans’ living resources.

[ Expertise in your inbox. Sign up for The Conversation’s newsletter and get a digest of academic takes on today’s news, every day. ]The Conversation

Nandini Ramesh, Postdoctoral Researcher in Earth and Planetary Science, University of California, Berkeley; James Rising, Assistant Professorial Research Fellow, London School of Economics and Political Science, and Kimberly Oremus, Assistant Professor of Marine Policy, University of Delaware

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