Under the moonlight: a little light and shade helps larval fish to grow at night



Jeffrey Shima, Author provided

Jeffrey Shima, Te Herenga Waka — Victoria University of Wellington; Craig W. Osenberg, University of Georgia; Stephen Swearer, The University of Melbourne, and Suzanne Alonzo, University of California, Santa Cruz

At night on any one of hundreds of coral reefs across the tropical Pacific, larval fish just below the sea surface are gambling on their chances of survival.

Our latest research shows the brightness of the Moon could play a major role in that struggle for survival by affecting the availability of prey and keeping predators away.

Understanding how that works could help in fisheries management, specifically the prediction of changes to harvested fish stocks that allow us to anticipate how many adult fish can be taken without destabilising the fishery.

Many fish populations experience boom-and-bust cycles largely because parents routinely produce millions of offspring that have very low, but fluctuating, survival rates.

The large number of larval fish that are produced means any environmental conditions — for example, increased nutrients — that improve survival odds even only marginally can lead to a big influx in the number of surviving offspring.

Several sixbar wrasse swim above a reef.
Adult sixbar wrasse in courtship.
Author?, Author provided

When the Sun goes down

In the past we failed to take into account the influences the night may have on fish development.

In our research we found the daily growth rates of the larvae of sixbar wrasse (Thalassoma hardwicke) around the island of Mo’orea, in French Polynesia, are strongly linked to phases of the Moon.




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Their growth appears to be maximised when the first half of the night is dark and the second half of the night is bright.

Cloudy nights obscure the Moon, and thus allowed us to check our models by contrasting growth on cloudy versus clear nights, which confirmed the effect of moonlight on growth of these fish.

Phases of the Moon

We found that on the best nights of the lunar month for sixbars, around the last Quarter Moon when the Moon rises around midnight, larval fish grew about 0.012mm a day more than average.

But on the worst nights, around the first Quarter Moon when the Moon is overhead at sunset and sets around midnight, they grew about 0.014mm a day less than average.

From First Quarter to Full Moon then Last Quarter.
Phases of the Moon from the Southern Hemisphere.
Wikimedia, CC BY-SA

For a typical larval sixbar of 37.5 days old, that means its growth is 24% more on the best night than on the worst one. This is important, as growth is inextricably linked to survival and ultimately fisheries productivity.

We think the Moon affects larval growth in this way because of how it changes the movements of deeper-dwelling animals, those that migrate into shallow water each night to hunt for food under the cover of darkness.

Zooplankton — potential prey for larval sixbars — respond quickly to the arrival of darkness, and move into the surface water to supplement the diets of sixbars.

Micronekton, such as lanternfishes, which hunt larval fishes, may take much longer to reach surface waters and seek out their prey, due to their migration from much deeper depths.

Four graphs showing different phases of the Moon and the amount of predator/prey during each phase.
Four graphs showing the larval fish (in yellow) and the amount of predator (red shading area) and prey (brown shading area) rising to the surface during each phase of he Moon.
Proceedings of the Royal Society B, Author provided

As a consequence, prey availability for sixbars in surface waters may be hindered by early nocturnal brightness while the arrival of predators may be impeded by late nocturnal brightness.

Thus, larval fish grow best when their predators are absent but their prey are abundant — around the last Quarter Moon.

In contrast, around the first Quarter Moon, prey are suppressed but predators are not, leading to the slowest growth.

During the New Moon, when the surface waters remain dark throughout the night, influxes of both prey and predators may be high, with the latter preventing the larval fish from enjoying the increased numbers of prey.

On the other hand, during the Full Moon, when surface waters are well-lit, the movement of prey and predators may be suppressed, reducing the risk to the fish but also eliminating their food.

Impact on fishing

More research is needed to quantify these lunar effects on other marine populations. But our findings to date are good news for those working to strengthen fisheries management, given that phases of the Moon are predictable and cloud cover that can modify moonlight is being measured by satellites.

A diver underwater keeping watch on one of the sixbar wrasse fish.
Observing the sixbar wrasse spawning.
Author?, Author provided

This makes the incorporation of moonlight into existing fisheries management models relatively simple.

We think this will have implications around the world, not just in the tropics. This is because the nightly upward movements of deep-water animals is ubiquitous — it is the largest mass migration of biomass on the planet, and it happens everywhere.

The suppressive effect of moonlight on this movement of potential predators and prey is also a global phenomenon.

We evaluated effects of the Moon on growth of larval temperate fish in an earlier study and found a similar effect (moonlight enhanced growth).




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The effect is stronger and more nuanced in our latest study, most likely because the waters in the tropics are comparatively clear.

Our findings also hint that other factors which affect night-time illumination of the sea may disrupt marine ecosystems. This includes the reflection of artificial lights from coastal cities, suspended sediments in the water column, and changes in cloud cover due to climate change.

In the future, we may be able to harness this extra information to help forecast fish population change to better guide the management and conservation of fisheries around the world.The Conversation

Jeffrey Shima, Professor of Ecology, Te Herenga Waka — Victoria University of Wellington; Craig W. Osenberg, Professor of Ecology, University of Georgia; Stephen Swearer, Professor of Marine biology, The University of Melbourne, and Suzanne Alonzo, Professor of Ecology & Evolutionary Biology, University of California, Santa Cruz

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

We found algae-farming fish that domesticate tiny shrimp to help run their farms



Longfin damselfish (left) have domesticated mysid shrimps (right).
Rohan Brooker, Author provided

William Feeney, Griffith University and Rohan Brooker, Deakin University

Humans are experts at domesticating other species and our world would be unrecognisable without it. There would be no cities, no supermarkets, and no pets. Domestication is a special kind of cooperative relationship, where one species provides prolonged support in exchange for a predictable resource.

While humans have domesticated various plants and animals, these relationships are surprisingly rare in other species. It’s true some insects (ants, beetles, and termites among them) domesticate fungi, but few other examples exist outside the insect world.

In our new study, we describe what appears to be first example of a non-human vertebrate domesticating another animal.

Reef in Belize
On the coral reefs off the coast of Belize, in Central America, longfin damselfish create, manage and feed from algae farms.
By Andy Blackledge – P4120130, CC BY 2.0, CC BY



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Farming fish domesticate shrimps

On the coral reefs off the coast of Belize, in Central America, longfin damselfish create, manage and feed from algae farms. We noticed they regularly have “swarms” of tiny crustaceans called mysid shrimps floating above their farms.

We found this unusual, as most farming damselfishes chase away anything that ventures near their farm. We were unsure why these species associated with one another, so we decided to try to find out what was going on.

First, to see whether mysid shrimps and farming damselfish are regularly found together, we ran a series of what’s known as “transects”. In other words, we conducted a series of 30 metre swims along the reef, and during each one we recorded each time we saw mysid shrimps, as well as whether they were near farming damselfish or other fish species.

We found these mysids were far more likely to be found near farming species, like the longfin damselfish, than other species.

The Smithsonian’s Carrie Bow Cay Marine Research Station off the coast of Belize.
Rohan Brooker

Next, we wanted to know if the mysids specifically seek out their damselfish partners.

So, we collected mysid shrimps from the field, brought them into the lab and exposed the mysids to water soaked with different things. For example, do they avoid the smell of a predator? Are they attracted to the smell of a farming damselfish?

We found the mysids shrimps were attracted to the longfin damselfish, repulsed by a predator and indifferent towards a non-farming fish — and to the farm itself.

I help you, you help me

Many fish eat mysid shrimps, so we ran an experiment to see if longfin damselfish provided protection to the mysids when they are in the fish’s farm.

To do this, we placed mysid shrimps in a clear plastic bag and placed the bag either inside or outside a farm.

We found that when placed outside a farm, other fish tried to eat the mysid shrimps. When inside the farms, any fish that tried to come close to the bag was chased off by the longfin damselfish. This suggested the mysids seek out longfin damselfish, as they provide mysids with protection from predators.

Slippery Dick Wrasse is a common predator of shrimps.
Slippery Dick Wrasse is a common predator of mysid shrimps.
Brian Gratwicke/Flickr, CC BY

One question remained: do the mysid shrimps provide a benefit to the longfin damselfish?

Given the damselfish eat the algae they farm, we thought maybe by hovering above the farm, the mysid shrimps waste might act as fertiliser.

To test this, we examined the quality of the algae within farms that did, or did not have mysid shrimps. We also examined the body condition of fish that did, or did not, have mysid shrimps within their farms.

We found farms with shrimps had higher quality algae, and fish from farms with mysid shrimps were in better condition.

Insight into how domestication happens

These different analyses together suggest longfin damselfish have domesticated mysid shrimps. The longfin damselfish provide a safe refuge, and in exchange the mysid shrimps provide the damselfish with fertiliser for its farm.

This relationship is important, because while fantastic research has provided insight into the history of domestication in our ancestors, these things happened in the distant past.

In the longfin damselfish, we can watch the early stages of domestication occur as it’s happening.

This is fascinating because it’s very similar to the proposed series of events that led to our domestication of species such as chickens, cats, dogs and pigs.




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The Conversation


William Feeney, Postdoctoral Research Fellow in Evolutionary Ecology, Griffith University and Rohan Brooker, Casual Research Fellow, Deakin University

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

Good news from the River Murray: these 2 fish species have bounced back from the Millennium Drought in record numbers



Shutterstock

Brenton Zampatti, CSIRO and Chris Bice

This year marks a decade since the end of the Millennium Drought, when flood waters reached the mouth of the River Murray in 2010. For 1,200 days prior, Australia’s most iconic river had ceased flowing to the sea, causing populations of fish and other aquatic animals to plummet.

In particular, native migratory fish, including congolli (Pseudaphritis urvilli) and pouched lamprey (Geotria australis), were severely impacted by barriers to migration — such as barrages and weirs — and a lack of river flow.

However, our research has shown some clever engineering and increasing volumes of water for the environment are helping congolli and pouched lamprey to bounce back in record numbers.

With native fish in the Murray-Darling Basin just a fraction of what they were before European colonisation, rebuilding populations will be a long process. But learning from successes like this along the way will aid in the journey toward a healthier river.

An adult female congolli
An adult female congolli. These fish will spend 3-4 years in the River Murray before returning to the ocean to spawn.
Brenton Zampatti, Author provided

What happened to fish in the Millennium Drought?

From 2001 to 2009, south-eastern Australia experienced the most severe drought in recorded history.

Unprecedented low rainfall and water extraction for irrigation and human consumption reduced water flows in the lower Murray by around 70%. Water levels in the Lower Lakes at the terminus of the river system fell to more than one metre below sea level.

To prevent saltwater from the ocean mixing with critical storages of freshwater, tidal barrages (dam-like structures) were closed, and the River Murray was disconnected from the sea.




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This was a big problem for a number of migratory species, including pouched lamprey and congolli, which need to migrate between freshwater and saltwater to complete their lifecycles.

During the Millennium Drought, no lamprey were seen in the Lower Lakes and Coorong, while numbers of juvenile congolli declined. After more than three years of barrage closure, local populations were threatened with extinction.

But in late 2010, both species were saved by major flooding, when the Murray once again flowed to the sea, and abundances have continued to steadily improve over the past decade.

Several management initiatives were also critical in supporting recovery, even through the most recent drought. Notably, the installation of fish ladders and better water management. Fish ladders are water-filled channels with a series of steps that enable fish to swim around or over dams and weirs.

A fish ladder on the Murray Barrages. Fish swim through this structure to move from the estuary.
into the freshwater lakes and River Murray. Without fish ladders, fish are seldom able to move past the barrages.

Brenton Zampatti, Author provided

Supporting fish migrations

Native fish populations in the Murray-Darling Basin are estimated to be approximately 10% of those pre-European settlement. Barriers to fish movement and altered river flows are two principal causes of decline.

The Murray Barrages were constructed in the 1930s, without consideration of fish passage, and it was 70 years before the first fish ladder was constructed in 2003.




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In 2020, there are now 11 fish ladders spread across the Murray Barrages, and our research has shown they effectively support vital migrations.

More fish ladders have been built on upstream weirs, together opening more than 2,000 kilometres of the River Murray to fish migration.

However, water must be available to operate the fish ladders, and this is where environmental water plays a role.

In 2009-10, approximately 120 gigalitres of environmental water were delivered across the Basin. By 2017-18, this volume was greater than 1,200 gigalitres and included substantial volumes across the Murray Barrages.




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This increase has enabled the River Murray to continuously flow to the sea, restoring its natural characteristics, albeit at a significantly reduced volume.

What’s more, water for the environment has supported constant operation of the barrage fish ladders since 2010 — a huge win for lamprey and congolli.

The bounce back

From the lows of the Millennium Drought we have so far this year caught a record 101 individual pouched lamprey moving through the barrage fish ladders and proceeding upstream. This is up from last year’s catch of 61 fish.

Pouched lamprey
Pouched lamprey has been found in record numbers.
Brenton Zampatti, Author provided

Congolli populuations are also booming. From 2007 to 2010, we sampled a combined total of just over 1,000 congolli. Compare this to the summer of 2014-15, when we sampled more than 200,000 passing through the fishways.

Congolli is now one of the most abundant fish in the Coorong and upstream of the barrages in the Lower Lakes.

What the rest of the basin can learn from this

Fish ladders and environmental water have been successful in supporting fish migration at the Murray Barrages, yet across the Murray-Darling Basin, thousands of barriers remain and more are being considered, particularly in the northern Basin.

These barriers can impede the movements of fish that migrate wholly within freshwater, such as golden perch (Macquaria ambigua) and the threatened silver perch (Bidyanus bidyanus). This includes the spawning migrations of adults and downstream dispersal of juveniles.

Mitigating the impacts of existing and new structures on the movement of fish is crucial to restoring native fish populations in the Murray-Darling Basin.

To help restore migratory fish throughout the basin, there must be greater understanding of the movement requirements of all fish life stages, the construction of effective fish ladders, and river flows must be sufficient to facilitate downstream movement, including of eggs and larval fish. The removal of barriers may also be a feasible option.

In any case, after 15 years of experience in the lower River Murray we’ve learnt protecting migratory fish is best achieved when researchers, the community, water managers and river operators collaborate closely. Such partnerships are the bedrock to establishing a healthier river.




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The Conversation


Brenton Zampatti, Principal Research Scientist, CSIRO and Chris Bice, Research scientist at SARDI

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

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.




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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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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.




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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.

Before and after: see how bushfire and rain turned the Macquarie perch’s home to sludge



Mannus Creek in NSW during the 2020 bushfire period.
Luke Pearce, Author provided

Lee Baumgartner, Charles Sturt University; Katie Doyle, Charles Sturt University; Luiz G M Silva, Charles Sturt University; Luke Pearce, and Nathan Ning, Charles Sturt University

This article is a preview of Flora, Fauna, Fire, a multimedia project launching on Monday July 13. The project tracks the recovery of Australia’s native plants and animals after last summer’s bushfire tragedy. Sign up to The Conversation’s newsletter for updates.


The unprecedented intensity and scale of Australia’s recent bushfires left a trail of destruction across Australia. Millions of hectares burned and more than a billion animals were affected or died. When the rains finally arrived, the situation for many fish species went from dangerous to catastrophic.

A slurry of ash and mud washed into waterways, turning freshwater systems brown and sludgy. Oxygen levels plummeted and water quality deteriorated rapidly.

Hundreds of thousands of fish suffocated. It was akin to filling your fish tank with mud and expecting your goldfish to survive.

Take, for example, the plight of the endangered Macquarie perch (Macquaria australasica), an Australian native freshwater fish of the Murray-Darling river system.

A Macquarie perch.
Luke Pearce, Author provided



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A special fish

Macquarie perch were once one of the most abundant fish in the Murray-Darling Basin. Revered by the community and once responsible for supporting extensive Indigenous, recreational, commercial and subsistence fisheries, they are an iconic species found nowhere else in the world. However, they have very specific needs.

Macquarie perch like rocky river sections with clear, fast-flowing water, shaded by trees and bushes on the banks.

Massive change wrought on our rivers over the past century means Macquarie perch are now only found at a handful of locations in the Murray-Darling Basin.

One habitat – Mannus Creek near the NSW Snowy Mountains – is particularly special because it was relatively pristine before the fires. In fact, this creek contained the last population of the threatened Macquarie perch in the NSW Murray catchment. A study in 2017 found a Macquarie perch population that was restricted to a 9km section of the creek but was doing quite well.

That was until bushfire rapidly swept through the catchment in January this year.

Some of us visited the creek three weeks after the fires. The intensity, ferocity and speed of the fires meant nothing was spared. The former forest floor was literally a trail of death and destruction – dead and charred kangaroos, wallabies, deer, possums and birds were everywhere.

All that remained of Mannus Creek was green pools in a blackened landscape, still smouldering days after the fire front passed. We immediately feared for the Macquarie perch we’d sampled, which were quite healthy less than a year before.

To our surprise, some Macquarie perch had survived. But with most of the catchment fully burnt, and no vegetation to stop runoff, we knew it was a ticking time bomb.

A desperate rescue attempt

With little time, we had to remove as many fish as possible from Mannus Creek before the rains arrived. The plan was to create an “insurance population” in case rain caused the water conditions to deteriorate.

We rescued ten fish. Days later, rain washed ash and silt into the channel. Within hours, the once-pristine creek became flowing mud with the consistency of cake mix.

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A government rescue team arrived a few days later to rescue more fish, and despaired at the “wall of ash and mud”.

An ark across Australia

Those ten individual Macquarie perch now live in an “ark” of at-risk species, spanning government and private hatchery facilities.

The ark is housing not only the Macquarie perch but other threatened species too. The rescued individuals, and perhaps their entire species, would have almost certainly perished during runoff events without these interventions.

Now a waiting game begins.

What next for the Macquarie perch?

Nobody knows for sure how many fish survived in Mannus Creek, nor how long it will take for the creek to recover. It could be years.

Ash and mud flow into Lake Macquarie after the fires.
Luke Pearce, Author provided

The challenge now is to support the rescued fish until it’s safe to either return them to the creek, or breed offspring and introduce them to their natural habitat.

Fish must be kept healthy and disease-free in captivity, and enough genetic diversity must be maintained for the population to remain viable.

If these rescued fish are held in captivity for too long, they might die. But equally worrying is that affected waterways may not recover in time to allow reintroduction.




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While maintaining the rescued populations, we must redouble our efforts to improve their natural habitats.

Burnt areas can allow pest plant and animal species to take hold and change habitats, so these threats need to be controlled. Finding similar, unburnt refuge areas is also crucial to prepare for future events and protect ecosystem resilience.

Working through these considerations – and quickly – is essential to giving these species the best hope of survival.

Funding, equipment and human resources are desperately needed to help our rivers recover. But we know that without an effective on-ground intervention, recovery could take decades.

For the iconic Macquarie perch, that would be too late.




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


The Conversation


Lee Baumgartner, Professor of Fisheries and River Management, Institute for Land, Water, and Society, Charles Sturt University; Katie Doyle, Freshwater Ecologist, Charles Sturt University; Luiz G M Silva, Freshwater Fish Scientist, Charles Sturt University; Luke Pearce, Fisheries Manager, and Nathan Ning, Freshwater Ecologist, Charles Sturt University

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.




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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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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.




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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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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.




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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.