No-take marine areas help fishers (and fish) far more than we thought



A juvenile Plectropomus leopardus from the Whitsundays.
David Williamson/James Cook University

Dustin Marshall, Monash University and Liz Morris, Monash University

One hectare of ocean in which fishing is not allowed (a marine protected area) produces at least five times the amount of fish as an equivalent unprotected hectare, according to new research published today.

This outsized effect means marine protected areas, or MPAs, are more valuable than we previously thought for conservation and increasing fishing catches in nearby areas.

Previous research has found the number of offspring from a fish increases exponentially as they grow larger, a disparity that had not been taken into account in earlier modelling of fish populations. By revising this basic assumption, the true value of MPAs is clearer.




Read more:
Protecting not-so-wild places helps biodiversity


Marine Protected Areas

Marine protected areas are ocean areas where human activity is restricted and at their best are “no take” zones, where removing animals and plants is banned. Fish populations within these areas can grow with limited human interference and potentially “spill-over” to replenish fished populations outside.

Obviously MPAs are designed to protect ecological communities, but scientists have long hoped they can play another role: contributing to the replenishment and maintenance of species that are targeted by fisheries.

Wild fisheries globally are under intense pressure and the size fish catches have levelled off or declined despite an ever-increasing fishing effort.

Yet fishers remain sceptical that any spillover will offset the loss of fishing grounds, and the role of MPAs in fisheries remains contentious. A key issue is the number of offspring that fish inside MPAs produce. If their fecundity is similar to that of fish outside the MPA, then obviously there will be no benefit and only costs to fishers.




Read more:
More fish, more fishing: why strategic marine park placement is a win-win


Big fish have far more babies

Traditional models assume that fish reproductive output is proportional to mass, that is, doubling the mass of a fish doubles its reproductive output. Thus, the size of fish within a population is assumed to be less important than the total biomass when calculating population growth.

But a paper recently published in Science demonstrated this assumption is incorrect for 95% of fish species: larger fish actually have disproportionately higher reproductive outputs. That means doubling a fish’s mass more than doubles its reproductive output.

When we feed this newly revised assumption into models of fish reproduction, predictions about the value of MPAs change dramatically.


Author provided

Fish are, on average, 25% longer inside protected areas than outside. This doesn’t sound like much, but it translates into a big difference in reproductive output – an MPA fish produces almost 3 times more offspring on average. This, coupled with higher fish populations because of the no-take rule means MPAs produce between 5 and 200 times (depending on the species) more offspring per unit area than unprotected areas.

Put another way, one hectare of MPA is worth at least 5 hectares of unprotected area in terms of the number of offspring produced.

We have to remember though, just because MPAs produce disproportionately more offspring it doesn’t necessarily mean they enhance fisheries yields.

For protected areas to increase catch sizes, offspring need to move to fished areas. To calculate fisheries yields, we need to model – among other things – larval dispersal between protected and unprotected areas. This information is only available for a few species.

We explored the consequences of disproportionate reproduction for fisheries yields with and without MPAs for one iconic fish, the coral trout on the Great Barrier Reef. This is one of the few species for which we had data for most of the key parameters, including decent estimates of larval dispersal and how connected different populations are.

No-take protected areas increased the amount of common coral trout caught in nearby areas by 12%.
Paul Asman and Jill Lenoble/Flickr, CC BY

We found MPAs do in fact enhance yields to fisheries when disproportionate reproduction is included in relatively realistic models of fish populations. For the coral trout, we saw a roughly 12% increase in tonnes of caught fish.

There are two lessons here. First, a fivefold increase in the production of eggs inside MPAs results in only modest increases in yield. This is because limited dispersal and higher death rates in the protected areas dampen the benefits.




Read more:
Caught on camera: Ancient Greenland sharks


However the exciting second lesson is these results suggest MPAs are not in conflict with the interests of fishers, as is often argued.

While MPAs restrict access to an entire population of fish, fishers still benefit from from their disproportionate affect on fish numbers. MPAs are a rare win-win strategy.

It’s unclear whether our results will hold for all species. What’s more, these effects rely on strict no-take rules being well-enforced, otherwise the essential differences in the sizes of fish will never be established.

We think that the value of MPAs as a fisheries management tool has been systematically underestimated. Including disproportionate reproduction in our assessments of MPAs should correct this view and partly resolve the debate about their value. Well-designed networks of MPAs could increase much-needed yields from wild-caught fish.The Conversation

Dustin Marshall, Professor, Marine Evolutionary Ecology, Monash University and Liz Morris, Administration Manager, Monash University

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

Advertisements

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


Robert Vertessy, University of Melbourne; Fran Sheldon, Griffith University; Lee Baumgartner, Charles Sturt University; Nick Bond, La Trobe University, and Simon Mitrovic, University of Technology Sydney

Over the recent summer, three significant fish death events occurred in the lower Darling River near Menindee, New South Wales. Species involved included Murray Cod, Silver Perch, Golden Perch and Bony Herring, with deaths estimated to be in the range of hundreds of thousands to over a million fish. These events were a serious ecological shock to the lower Darling region.

Our report for the Minister for Agriculture and Water Resources examines the causes of these events and recommend actions to mitigate the potential for repeat events in the future.

The final report has just been released, summarising what we found and what we recommend.

Causes of the fish deaths

High-flow events in the Darling River in 2012 and 2016 filled the Menindee Lakes and offered opportunities for substantial fish breeding, further aided by the targeted use of environmental water.

The result was very large numbers of fish in the lakes, river channels and weir pools around Menindee. After the lake-filling rains of late 2016, two very dry years ensued, resulting in very low inflows into the Barwon-Darling river.

As the supply of water dried up, the river became a series of disconnected and shrinking pools. As the extremely hot and dry conditions in late 2018 took hold, the large population of fish around Menindee became concentrated within weir pools.

Hot weather, low rainfall and low flows provided ideal conditions for algal blooms and thermal stratification in the weir pools, resulting in very low oxygen concentrations within the bottom waters.

With the large fish population now isolated to the oxygenated surface waters of the pools, all that was needed for the fatal blow was a trigger for the water profile to mix. Such a trigger arrived on three separate occasions, with changes in the weather that brought sudden drops in temperature and increased wind that caused sudden turnover of the low-oxygen bottom waters.

Summary of the multiple causes of the 2018-19 fish death events in the lower Darling river.

With the fish already stressed by high temperatures, they were now unable to gain enough oxygen from the water to breathe, and a very large number of them died. As we write, the situation in the lower Darling remains dire, and there is a risk of further fish deaths if there are no significant inflows to the river.

Fish deaths caused by these sorts of turnover events are not uncommon, but the conditions outlined above made these events unusually dramatic.

So, how did such adverse conditions arise in the lower Darling river and how might we avoid their reoccurrence? We’ve examined four influencing factors: climate, water management, lake operations, and fish mobility.

Key influencing factors

We found that the fish death events in the lower Darling were preceded and affected by exceptional climatic conditions.

Inflows to the water storages in the northern Basin over 2017-18 were the second lowest for any two-year period on record. Most of the Murray-Darling Basin experienced its hottest summer on record, exemplified by the town of Bourke breaking a new heatwave record for NSW, with 21 consecutive days with a maximum temperature above 40℃.

We concluded that climate change amplified these conditions and will likely result in more severe droughts in the future.

Changes in the water access arrangements in the Barwon–Darling River, made just prior to the commencement of the Basin Plan in 2012, exacerbated the effects of the drought. These changes enhanced the ability of irrigators to access water during low flow periods, meaning fewer flow pulses make it down the river to periodically reconnect and replenish isolated waterholes that provide permanent refuge habitats for fish during drought.

We conclude that the Lake Menindee scheme had been operated according to established protocols, and was appropriately conservative given the emerging drought conditions. But low connectivity in the lower Darling resulted in poor water quality and restricted mobility for fish.

Recommended policy and management actions

Given the right mix of policy and management actions, Basin governments can significantly reduce the risks of further fish death events and promote the recovery of affected fish populations.

The Basin Plan is delivering positive environmental outcomes and more benefits will accrue once the plan is fully implemented. But more needs to be done to enhance river connectivity and protect low flows, first flushes and environmental flow releases in the Barwon-Darling river.

Drought resilience in the lower Darling can be enhanced by reconfiguring the Lake Menindee Water Savings Project, modifying the current Menindee Lakes operating rules and purchasing high security water entitlements from horticultural enterprises in the region.

In Australia, water entitlements are the rights to a share of the available water resource in any season. Irrigators get less (or no) water in dry (or extremely dry) years.

A high-security water entitlement is one with a high chance of receiving the full water allocation. In some systems, although not all, this is expected to happen 95 per cent of the time. And these high-security entitlements are the most valuable and sought after.

Fish mobility can be enhanced by removing barriers to movement and adding fish passageways.

It would be beneficial for environmental water holders to place more of their focus on sustaining fish populations through drought sequences.

The river models that governments use to plan water sharing need to be updated more regularly to accurately represent the state of Basin development, configured to run on a whole-of-basin basis, and improved to more faithfully represent low flow conditions.

There are large gaps in water quality monitoring, metering of water extractions and basic hydro-ecologic knowledge that should be filled.

Risk assessments need to be undertaken to identify likely fish death event hot spots and inform future emergency response plans.

All of these initiatives need to be complemented by more sophisticated and reliable assessments of the impacts of climate change on water security across the Basin.

Governments must accelerate action

Responding to the lower Darling fish deaths in a prompt and substantial manner provides governments an opportunity to redress some of the broader concerns around the management of the Basin.

To do so, Basin governments must increase their political, bureaucratic and budgetary support for high value reforms and programs, particularly in the northern Basin.

All of our recommendations can be implemented within the current macro-settings of the Basin Plan and do not require a revisiting of the challenging socio-political process required to define Sustainable Diversion Limits (SDLs).

Successful implementation will require a commitment to authentic collaboration between governments, traditional owners, local communities, and sustained input from the science community.


The authors would like to acknowledge the contribution of Daren Barma, Director of Barma Water Consulting, to this article.

A version of this article has been published in Pursuit.The Conversation

Robert Vertessy, Enterprise Professor, University of Melbourne; Fran Sheldon, Professor, Australian Rivers Institute, Griffith University, Griffith University; Lee Baumgartner, Associate Research Professor (Fisheries and River Management), Institute for Land, Water, and Society, Charles Sturt University; Nick Bond, Professor of Freshwater Ecology and Director of the Centre for Freshwater Ecosystems, La Trobe University, and Simon Mitrovic, Associate Professor, University of Technology Sydney

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

More fish, more fishing: why strategic marine park placement is a win-win



File 20190325 36267 6gisnm.jpg?ixlib=rb 1.1
Marine parks are good for fish – especially if they’re in the right areas.
Epstock/Shutterstock

Kerstin Jantke, University of Hamburg; Alienor Chauvenet, Griffith University; Hugh Possingham, The University of Queensland; James Allan, The University of Queensland; James Watson, The University of Queensland, and Kendall Jones, The University of Queensland

Australia has some of the most spectacular marine ecosystems on the planet – including, of course, the world-famous Great Barrier Reef. Many of these places are safe in protected areas, and support a myriad of leisure activities such as recreational fishing, diving and surfing. No wonder eight in ten Aussies live near the beach.

Yet threats to marine ecosystems are becoming more intense and widespread the world over. New maps show that only 13% of the oceans are still truly wild. Industrial fishing now covers an area four times that of agriculture, including the farthest reaches of international waters. Marine protected areas that restrict harmful activities are some of the last places where marine species can escape. They also support healthy fisheries and increase the ability of coral reefs to resist bleaching.




Read more:
Most recreational fishers in Australia support marine sanctuaries


One hundred and ninety-six nations, including Australia, agreed to international conservation targets under the United Nations Convention on Biological Diversity. One target calls for nations to protect at least 10% of the world’s oceans. An important but often overlooked aspect of this target is the requirement to protect a portion of each of Earth’s unique marine ecosystems.

How are we tracking?

The world is on course to achieve the 10% target by 2020, with more than 7.5% of the ocean already protected. However, our research shows that many marine protected areas are located poorly, leaving many ecosystems underprotected or not protected at all.

What’s more, this inefficient placement of marine parks has an unnecessary impact on fishers. While marine reserves typically improve fisheries’ profitability in the long run, they need to be placed in the most effective locations.

We found that since 1982, the year nations first agreed on international conservation targets, an area of the ocean almost three times the size of Australia has been designated as protected areas in national waters. This is an impressive 20-fold increase on the amount of protection that was in place beforehand.

But when we looked at specific marine ecosystems, we found that half of them fall short of the target level of protection, and that ten ecosystems are entirely unprotected. For example, the Guinea Current off the tropical West African coast has no marine protected areas, and thus nowhere for its wildlife to exist free from human pressure. Other unprotected ecosystems include the Malvinas Current off the southeast coast of South America, Southeast Madagascar, and the North Pacific Transitional off Canada’s west coast.

Marine park coverage of global ecosystems. Light grey: more than 10% protection; dark grey: less than 10% protection; red: zero protection.
Author provided

Australia performs comparatively well, with more than 3 million square km of marine reserves covering 41% of its national waters. Australia’s Coral Sea Marine Park is one of the largest marine protected areas in the world, at 1 million km². However, a recent study by our research group found that several unique ecosystems in Australia’s northern and eastern waters are lacking protection.

Furthermore, the federal government’s plan to halve the area of strict “no-take” protection inside marine parks does not bode well for the future.

How much better can we do?

To assess the scope for improvement to the world’s marine parks, we predicted how the protected area network could have been expanded from 1982.

With a bit more strategic planning since 1982, the world would only need to conserve 10% of national waters to protect all marine ecosystems at the 10% level. If we had planned strategically from as recently as 2011, we would only need to conserve 13% of national waters. If we plan strategically from now on, we will need to protect more than 16% of national waters.

If nations had planned strategically since 1982, the world’s marine protected area network could be a third smaller than today, cost half as much, and still meet the international target of protecting 10% of every ecosystem. In other words, we could have much more comprehensive and less costly marine protection today if planning had been more strategic over the past few decades.

The lack of strategic planning in previous marine park expansions is a lost opportunity for conservation. We could have met international conservation targets long ago, with far lower costs to people – measured in terms of a short-term loss of fishing catch inside new protected areas.

This is not to discount the progress made in marine conservation over the past three decades. The massive increase of marine protected areas, from a few sites in 1982, to more than 3 million km² today, is one of Australia’s greatest conservation success stories. However, it is important to recognise where we could have done better, so we can improve in the future.

Australia’s marine park network.
Author provided

This is also not to discount protected areas. They are important but can be placed better. Furthermore, long-term increases in fish populations often outweigh the short-term cost to fisheries of no-take protected areas.

Two steps to get back on track

In 2020, nations will negotiate new conservation targets for 2020-30 at a UN summit in China. Targets are expected to increase above the current 10% of every nation’s marine area.

We urge governments to rigorously assess their progress towards conservation targets so far. When the targets increase, we suggest they take a tactical approach from the outset. This will deliver better outcomes for nature conservation, and have less short-term impact on the fishing industry.




Read more:
More than 1,200 scientists urge rethink on Australia’s marine park plans


Strategic planning is only one prerequisite for marine protected areas to effectively protect unique and threatened species, habitats and ecosystems. Governments also need to ensure protected areas are well funded and properly managed.

These steps will give protected areas the best shot at halting the threats driving species to extinction and ecosystems to collapse. It also means these incredible places will remain available for us and future generations to enjoy.The Conversation

Kerstin Jantke, Postdoctoral Researcher on conservation biology, University of Hamburg; Alienor Chauvenet, Lecturer, Griffith University; Hugh Possingham, Professor, The University of Queensland; James Allan, Postdoctoral research fellow, School of Biological Sciences, The University of Queensland; James Watson, Professor, The University of Queensland, and Kendall Jones, PhD candidate, Geography, Planning and Environmental Management, The University of Queensland

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

It’s fish on ice, as frozen zoos make a last-ditch attempt to prevent extinction


Nicola Marie Rivers, Monash University

Twenty-six of the forty-six fish species known to live in the Murray-Darling basin are listed as rare or threatened. Recent fish kills in the iconic river system are a grim reminder of how quickly things can take a turn for the worst.

A sudden drop in population size can push a species towards extinction, but there may be hope for resurrection. Frozen zoos store genetic material from endangered species and are preparing to make new individuals if an extinction occurs.




Read more:
Cryopreservation: the field of possibilities


Unfortunately, poor response to freezing has hindered the introduction of fish into frozen zoos in the past. Now new techniques may provide them safe passage.

Ice ice baby

A frozen zoo, also known as a biobank or cryobank, stores cryopreserved or “frozen” cells from endangered species. The primary purpose of a frozen zoo is to provide a backup of endangered life on Earth allowing us to restore extinct species.

Reproductive cells, such as sperm, oocytes (eggs) and embryos, are cooled to -196ºC, at which point all cellular function is paused. When a sample is needed, the cells are warmed and used in breeding programs to produce new individuals, or to study their DNA to determine genetic relationships with other species.

There are several cryobanking facilities in Australia, including the Australian Frozen Zoo (where I work), the CryoDiversity Bank and the Ian Potter Australian Wildlife Biobank, as well as private collections. These cryobanks safeguard some of Australia’s most unique wildlife including the greater bilby, the golden bandicoot, and the yellow-footed rock wallaby as well as other exotic species such as the black rhino and orangutans.

Internationally, frozen zoos are working together to build a “Noah’s Ark” of frozen tissue. The Frozen Ark project, established in 2004 at the University of Nottingham, now consists of over 5,000 species housed in 22 facilities across the globe.

The Manchurian trout, or lenok, is the only fish successfully reproduced through cryopreservation and surrogacy.
National Institute of Ecology via Wikimedia, CC BY

Less love for fish

As more and more species move into frozen zoos, fish are at risk of being left out. Despite years of research, no long-term survival has been reported in fish eggs or embryos after cryopreservation. However, precursors of sperm and eggs known as gonial cells found in the developing embryo or the ovary or testis of adult fish have been preserved successfully in several species including brown trout, rainbow trout, tench and goby.

By freezing these precursory cells, we now have a viable method of storing fish genetics but, unlike eggs and sperm, the cells are not mature and cannot be used to produce offspring in this form.

To transform the cells into sperm and eggs, they are transplanted into a surrogate fish. Donor cells are injected into the surrogate where they follow instructions from surrounding cells which tell them where to go and when and how to make sperm or eggs.

Once the surrogate is sexually mature they can mate and produce offspring that are direct decedents of the endangered species the donor cells were originally collected from. In a way, we are hijacking the reproductive biology of the surrogate species. By selecting surrogates that are prolific breeders we can essentially “mass produce” sperm and eggs from an endangered species, potentially producing more offspring than it would have been able to within its own lifetime.

Cell surrogacy has been successful in sturgeon, rainbow trout and zebrafish.

The combination of cryopreservation and surrogacy in conservation is promising but has only successfully been used in one endangered species so far, the Manchurian trout.

Not a get-out-of-conservation card

The “store now, save later” strategy of frozen zoos sounds simple but alas it is not. The methods needed to reproduce many species from frozen tissue are still being developed and may take years to perfect. The cost of maintaining frozen collections and developing methods of resurrection could divert funding from preventative conservation efforts.

Even if de-extinction is possible, there could be problems. The Australian landscape is evolving – temperatures fluctuate, habitats change, new predators and diseases are being introduced. Extinction is a consequence of failing to adapt to these changes. Reintroducing a species into the same hostile environment that lead to its demise may be a fool’s errand. How can we ensure reintroduced animals will thrive in an environment they may no longer be suited for?

Reducing human impact on the natural environment and actively protecting threatened species will be far easier than trying to resurrect them once they are gone. In the case of the Murray Darling Basin, reversing the damage done and developing policies that ensure its long-term protection will take time that endangered species may not have.




Read more:
I’ve always wondered: does anyone my age have any chance of living for centuries?


Frozen zoos are an insurance policy, and we don’t want to have to use them. But if we fail in our fight against extinction, we will be glad we made the investment in frozen zoos when we had the chance.The Conversation

Nicola Marie Rivers, PhD Candidate, Monash University

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

Damning royal commission report leaves no doubt that we all lose if the Murray-Darling Basin Plan fails


Jamie Pittock, Australian National University

In the wake of revelations of water theft, fish kills, and towns running out of water, the South Australian Royal Commission into the Murray-Darling Basin has reported that the Basin Plan must be strengthened if there is to be any hope of saving the river system, and the communities along it, from a bleak future.

Evidence uncovered by the Royal Commission showed systemic failures in the implementation of the Murray-Darling Basin Plan. The damning report must trigger action by all governments and bodies involved in managing the basin.

The Basin Plan was adopted in 2012 to address overallocation of water to irrigated farming at the expense of the environment, river towns, Traditional Owners, and the pastoral and tourism industries.

The Commission has made 111 findings and 44 recommendations that accuse federal agencies of maladministration, and challenge key policies that were pursued in implementing the plan.




Read more:
Aboriginal voices are missing from the Murray-Darling Basin crisis


What did the report find?

The commission found that the Basin Plan breached federal water laws by applying a “triple bottom line” trade-off of environmental and socioeconomic values, rather than prioritising environmental sustainability and then optimising socio-economic outcomes.

I and my colleagues in the Wentworth Group of Concerned Scientists provided evidence to the commission from our independent assessment of the Basin Plan in 2017, which the commission’s findings reflect.

Contrary to current government practices, the Commission recommendations include:

  • prioritising environmental sustainability
  • basing the plan on transparent science
  • acquiring more water for the environment through direct purchase from farmers
  • meeting the water needs of the Basin’s 40 Indigenous nations
  • ensuring that state governments produce competent subsidiary plans and comply with agreements to remove constraints to inundating floodplain wetlands
  • addressing the impacts of climate change
  • improving monitoring and compliance of Basin Plan implementation.

Resilience in decline

The Murray-Darling Basin is not just a food bowl. It is a living ecosystem that depends on interconnected natural resources. It also underpins the livelihoods of 2.6 million people and agricultural production worth more than A$24 billion.

The continued health of the basin and its economy depends on a healthy river – which in turns means healthy water flows. Like much of Australia, the Murray-Darling Basin is subject to periods of “droughts and flooding rains”. But over the past century the extraction of water, especially for irrigation, has reduced river flows to a point at which the natural system can no longer recover from these extremes.

That lack of resilience is evidenced by the current Darling River fish kills. More broadly, overextraction risks the health of the entire basin, and its capacity to sustain productive regional economies for future generations.

From the perspective of the Wentworth Group, we support the commission’s main recommendations, including increasing pressure on recalcitrant state governments to responsibly deliver their elements of the plan, and to refocus on the health of the river.

We particularly support recommendations related to the use of the best available science in decision-making, including for managing declining water availability under a changing climate.

We welcome the recommendation to reassess the sustainable levels of water extraction so as to comply with the Commonwealth Water Act. These must be constructed with a primary focus on the environment.

In line with this, the 70 billion litre reduction in environmental water from the northern basin adopted by parliament in 2018 should be immediately repealed. So should the ban on direct buyback of water from farmers for the environment.

We also recognise that the Basin Plan’s water recovery target is insufficient to restore health to the environment and prevent further damage, and would welcome an increase in the target above 3,200 billion litres.




Read more:
A good plan to help Darling River fish recover exists, so let’s get on with it


South Australian Premier Steven Marshall has taken a welcome first step in calling for a Council of Australian Governments meeting to discuss the commission’s findings. Our governments need to avoid the temptation to legislate away the politically inconvenient failings exposed by the commission, and instead act constructively and implement its recommendations.

This is not only a challenge for the current conservative federal government. The Labor side of politics needs to address its legacy in establishing the Murray-Darling Basin Authority and the Basin Plan, as well as the Victorian government’s role in frustrating the plan’s implementation by failing to remove constraints to environmental water flows.

Now, more than ever, we need strong leadership. If the Murray-Darling Basin Plan fails, we all lose.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.

How did the fish cross the road? Our invention helps them get to the other side of a culvert



File 20180924 129868 4v1wjx.jpg?ixlib=rb 1.1
When a stream enters a culvert, the flow can be concentrated so much that water flows incredibly fast. So fast, in fact, that small and juvenile fish are unable to swim against the flow and are prevented from reaching where they need to go to eat, reproduce or find safety.
Shutterstock

Jabin Watson, The University of Queensland; Craig E. Franklin, The University of Queensland; Harriet Goodrich, University of Exeter; Jaana Dielenberg, The University of Queensland, and Rebecca L. Cramp, The University of Queensland

Fish need to move to find food, escape predators and reach suitable habitat for reproduction. Too often, however, human activities get in the way. Dams, weirs and culverts (the tunnels and drains often found under roads) can create barriers that fragment habitats, isolating fish populations.

An Australian innovation, however, promises to help dwindling fish populations in Australia and worldwide. Our solution, recently described in Ecological Engineering, tackles one of the greatest impediments to fish migration in Australia: culverts.

A culvert crisis in our waterways

Freshwater ecosystems are one of the most heavily impacted by human activities.

Many freshwater species, such as the iconic barramundi, start their life as larvae in estuaries, then as small juveniles they make mammoth upstream migrations to freshwater habitats. In fact, about half of the freshwater fish species in southeast Australia need to migrate as part of their life cycle.

When fish are unable to pass human-made barriers, the decline in populations can be huge. For example, in the Murray-Darling Basin where there are thousands of barriers and flows are highly regulated, fish numbers are estimated to be at only 10% of pre-European numbers.

In New South Wales alone, there are more than 4,000 human-made barriers to fish passage. Over half of these are culverts. Culverts are most often installed to allow roads to cross waterways. They are designed to move water under the road, which they do quite efficiently, but often with no consideration of the requirements of the animals that live there.

When a stream enters a culvert, the flow can be concentrated so much that water flows incredibly fast. So fast, in fact, that small and juvenile fish are unable to swim against the flow and are prevented from reaching where they need to go to eat, reproduce or find safety.

A map of human-made barriers to fish passage in NSW. Image: Fisheries NSW.

Many current design ‘fixes’ come with problems

The problem culverts pose for fish is now well acknowledged by fisheries managers, and as a result efforts to make culverts fish-friendly are now widespread.

Where space allows, these new fish passage solutions can resemble a natural stream, where rocks of various sizes are added to break up the flow. Alternatively, artificial baffles (barriers to break up and slow the flow) are also commonly attached to the walls of the tunnel.

These designs do have some drawbacks. They may suit some fish sizes and species, but not all. They can be expensive to install. They also tend to catch debris, which increases maintenance costs and the risk of flooding upstream during high flow events.

A box culvert running under a road.
Shutterstock

Using physics to find a new solution

We took a new approach that harnesses a property of fluid mechanics that scientists call the “boundary layer”. When a fluid moves over a solid surface, friction causes the water to slow down next to the surface. This thin layer of slower-moving water is called the boundary layer.

Where two surfaces meet, such as in the corner of a square culvert, the boundary layers of the bed and wall merge. This creates a small area of slower-moving water – the “reduced velocity zone” – right in the corner. This is quite small, but little fish can still use it and are very good at finding it.

We wanted to expand this zone (to accommodate a wider range of fish sizes) and slow the water in it further.

So, we added a third surface, generating three boundary layers that then joined. This was done by adding a square beam running the length of the channel wall, close to the floor. The boundary layers of the floor, wall and bottom surface of the beam merged to create a reduced velocity channel along the side of the main flow.

In this GIF to the right hand side, the reduced velocity zone is revealed by adding a fluorescent dye, which lingers in the slower flowing water under the square beam we added to the channel.

Testing our design in a 12 metre channel (or flume) found that water velocity in the zone below the beam was slowed by up to 30%. For small fish, this is a huge reduction.

In tests, we focused on small-bodied species, or juveniles of larger growing species, because these are considered the weakest swimming size class and most vulnerable to high water velocities created within culverts. Every species tested saw significant improvements in their ability to swim and traverse up the channel.

All of the species benefited, regardless of their body shape or swimming style.

The GIF on the right hand side here shows a juvenile Murray cod swimming upstream using the reduced velocity zone we created by adding the beam.

Creating a slower-flowing zone

Our novel fish passage design is highly effective, yet very simple. It’s a square beam installed along the length of a culvert wall, so it’s easy to incorporate into new structures and cheap to retrofit into existing culverts.

It is also much less likely to trap debris than baffles or rocks embedded in the floor of a culvert.

This is a totally new approach that has the potential for widespread application, helping to restore the connectivity of freshwater fish populations here in Australia, and overseas.

A Crimson-spotted rainbowfish navigates the fast flow by swimming under the beam we added to channel.
Harriet Goodrich, Author provided
You can see the beam more clearly here. A Crimson-spotted rainbowfish swims under the beam we added to slow the water flow in that area.
Harriet Goodrich, Author provided

More research lies ahead. We’re hoping that by optimising the dimensions of the beam we can get even more fish through the channels, with even greater ease. We’re also planning field testing to check our laboratory findings work in the real world.

Freshwater biodiversity is greatest in the tropics. Here, developing countries are having drastic impacts on their freshwater ecosystems. The simplicity of this design may make it an affordable approach to help maintain and restore habitat connectivity in developing regions.

Matthew Gordos from NSW Fisheries contributed to this article.The Conversation

Jabin Watson, Postdoctoral researcher, The University of Queensland; Craig E. Franklin, Professor in Zoology, The University of Queensland; Harriet Goodrich, PhD student, University of Exeter; Jaana Dielenberg, Science Communication Manager, The University of Queensland, and Rebecca L. Cramp, Senior Research Fellow, The University of Queensland

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

The 2016 Great Barrier Reef heatwave caused widespread changes to fish populations



File 20180725 194140 1cri4pn.jpg?ixlib=rb 1.1
Some fish fared better than others amid the extreme temperatures of the 2016 heatwave.
Rick Stuart-Smith/Reef Life Survey

Rick Stuart-Smith, University of Tasmania; Christopher Brown, Griffith University; Daniela Ceccarelli, James Cook University, and Graham Edgar, University of Tasmania

The 2016 marine heatwave that killed vast amounts of coral on the Great Barrier Reef also caused significant changes to fishes and other animals that live on these reefs.

Coral habitats in the Great Barrier Reef (GBR) and in the Coral Sea support more than 1,000 fish species and a multitude of other animals. Our research, published in Nature today, documents the broader impact across the ecosystem of the widespread coral losses during the 2016 mass coral bleaching event.

While a number of fish species were clearly impacted by the loss of corals, we also found that many fish species responded to the increased temperatures, even on reefs where coral cover remained intact. The fish communities in the GBR’s southern regions became more like those in warmer waters to the north, while some species, including parrotfishes, were negatively affected by the extreme sea temperatures at the northern reefs.




Read more:
How the 2016 bleaching altered the shape of the northern Great Barrier Reef


The loss of coral robs many fish species of their preferred food and shelter. But the warming that kills coral can also independently cause fish to move elsewhere, so as to stay within their preferred temperature range. Rising temperatures can also have different effects on the success, and therefore abundance, of different fish populations.

One way to tease apart these various effects is to look at changes in neighbouring reefs, and across entire regions that have been affected by bleaching, including reefs that have largely escaped coral loss.

We were able to do just this, with the help of highly trained volunteer divers participating in the Reef Life Survey citizen science program. We systematically surveyed 186 reefs across the entire GBR and western Coral Sea, both before and after the 2016 bleaching event. We counted numbers of corals, fishes, and mobile invertebrates such as sea urchins, lobsters and giant clams.

Sea temperatures and coral losses varied greatly between sites, which allowed us to separate the effects of warming from coral loss. In general, coral losses were much more substantial in areas that were most affected by the prolonged warmer waters in the 2016 heatwave. But these effects were highly patchy, with the amount of live hard coral lost differing significantly from reef to reef.

For instance, occasional large losses occurred in the southern GBR, where the marine heatwave was less extreme than at northern reefs. Similarly, some reefs in the north apparently escaped unscathed, despite the fact that many reefs in this region lost most of their live corals.

Sea temperatures the culprit

Our survey results show that coral loss is just one way in which ocean warming can affect fishes and other animals that depend on coral reefs. Within the first year after the bleaching, the coral loss mostly affected fish species that feed directly on corals, such as the butterflyfishes. But we also documented many other changes that we could not clearly link to local coral loss.

Much more widespread than the impacts of the loss of hard corals was a generalised response by the fish to warm sea temperatures. The 2016 heatwave caused a mass reshuffling of fish communities across the GBR and Coral Sea, in ways that reflect the preferences of different species for particular temperatures.

In particular, most reef-dwelling animals on southern (cooler) reefs responded positively to the heatwave. The number of individuals and species on transect counts generally increased across this region.

By contrast, some reefs in the north exceeded 32℃ during the 2016 heatwave – the typical sea temperature on the Equator, the hottest region inhabited by any of the GBR or Coral Sea species.

Some species responded negatively to these excessive temperatures, and the number of observations across surveys in their northernmost populations declined as a consequence.

Parrotfishes were more affected than other groups on northern reefs, regardless of whether their local reefs suffered significant coral loss. This was presumably because the heatwave pushed sea temperatures beyond the level at which their populations perform best.

Nothing to smile about: some parrotfishes don’t do well in extreme heat.
Rick Stuart-Smith/Reef Life Survey

Local populations of parrotfishes will probably bounce back after the return of cooler temperatures. But if similar heatwaves become more frequent in the future, they could cause substantial and lasting declines among members of this ecologically important group in the warmest seas.

Parrotfishes are particularly important to the health of coral reef ecosystems, because their grazing helps to control algae that compete with corals for habitat space.




Read more:
How the 2016 bleaching altered the shape of the northern Great Barrier Reef


A key message from our study is not to overlook the overarching influence of temperature on coral reef ecosystems – and not to focus solely on the corals themselves.

Even if we can save some corals from climate change, such as with more stress-tolerant breeds of coral, we may not be able to stop the impacts of warming seas on fish.

Future ecological outcomes will depend on a complex mix of factors, including fish species’ temperature preferences, their changing habitats, and their predators and competitors. These impacts will not always necessarily be negative for particular species and locations.

The ConversationOne reason for hope is that positive responses of many fish species in cooler tropical regions may continue to support healthy coral reef ecosystems, albeit in a different form to those we know today.

Rick Stuart-Smith, Research Fellow, University of Tasmania; Christopher Brown, Research Fellow, Australian Rivers Institute, Griffith University; Daniela Ceccarelli, Adjunct Senior Research, ARC Centre of Excellence for Coral Reef Studies, James Cook University, and Graham Edgar, Senior Marine Ecologist, Institute for Marine and Antarctic Studies, University of Tasmania

This article was originally published on The Conversation. Read the original article.