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IUCN survey suggests that almost half of Caribbean freshwater fish are threatened with extinction

July 31, 2021
The Zapata swamp in Cuba, home to the critically endangered ‘living fossil’ Cuban gar, which is increasingly threatened by the spread of non-native catfish. Image: Marjon Melissen | Flickr Creative Commons

The Caribbean islands are home to a rich diversity of freshwater life, including 79 species of fish which are unique to the region’s shallow streams, lakes and wetlands. However, a new IUCN survey suggests that 41% of Caribbean freshwater fish are threatened with extinction.

The survey represents the first comprehensive assessment of freshwater fish populations in the Caribbean. It shows that fifty-four of the region’s fish species are endemic to the two largest islands, Cuba and Hispaniola, with fewer other endemics found on smaller islands.

“Freshwater fishes are one of the most threatened groups of vertebrates on the planet,” says Tim Lyons, Species Survival Officer at the ABQ BioPark and project coordinator for the assessment. “When you think of the Caribbean, the first thing that comes to mind are visions of beaches and coral reefs, but freshwater fishes are just as important. We depend on them and the watersheds they live in for everything from food to energy.”

The survey suggests that freshwater fish populations in the Caribbean are subject to multiple pressures, including habitat loss, pollution and the spread of invasive non-native species. Whilst its findings are stark, it is hoped that the survey will provide a basis for conservationists and local communities to develop plans to conserve and restore freshwater ecosystems across the region.

“This new assessment sheds light on the critical need for directing more resources to conserving the unique freshwater fishes of the Caribbean, given they face a risk of extinction higher than the global average and include many species found nowhere else on Earth,” says Dr. Harmony Patricio, Conservation Programme Manager for Shoal.

A Jumbie Teta (Ancistrus trinitatis) on a shallow streambed in Trinidad. The species was assessed as Near Threatened due to its limited range and continuing habitat decline associated with human pressures. Image: Amy Deacon.

“Beyond the species known so far, the insular Caribbean holds an incredibly valuable diversity of freshwater fishes still to be discovered, described and understood,” adds Dr. Jose Ponce de Leon from the IUCN freshwater fish working group. “This IUCN report shows the overwhelming need of protecting Caribbean freshwater habitats and educating ourselves and others about their values and threats. This project is an important step in identifying conservation priorities in the Caribbean and highlights the value of collaborative research and inclusive strategic alliances for conservation biology.”

The spread of invasive non-native species was highlighted by the survey as a significant threat to freshwater fish populations in the Caribbean. Native to the Zapata swamp in Cuba, the Cuban gar can reach over two metres in length. Known as a ‘living fossil’, barely changed since the late Jurassic period, the Cuban gar plays an important apex predator role in wetland food webs. 

However, the spread of the African walking catfish (or ‘claria’) to the island following aquaculture introductions has significantly impacted populations of Cuban gar and other fish species. The catfish are large, mobile and predatory, and can outcompete gar and other species. As a result, the Cuban gar is now listed by the IUCN as critically endangered.

A juvenile Cuban gar. Image: Erik Garcia-Machado

Another key pressure highlighted by the survey is ongoing habitat loss and pollution. For example, Lake Miragoane is a coastal freshwater lake on the Tiburon Peninsula of southwestern Haiti. The lake supports 10 critically endangered fish species from the genus Limia – tiny livebearing fish – which are found nowhere else in the world. However, their populations are increasingly threatened by water pollution and deforestation around the lake.

“The primary threats to freshwaters in the Caribbean are consistent with the threats that are driving extinction in other parts of the world, and the extinction risk that these species face is a clear indicator of an ecosystem in distress,” suggests Tim Lyons. “The IUCN has declared 80 species of freshwater fishes extinct, with hundreds more likely to have gone extinct before their formal description or assessment on the IUCN Red List. We must act now to prevent unique Caribbean species from joining them.”

“These assessments are a critical step towards the conservation of freshwater fishes in the Caribbean,” says Dr. Yolanda León, President of Grupo Jaragua, an organisation based in the Dominican Republic which works on biodiversity conservation on Hispaniola.

Grupo Jaragua led the recent submission of an IUCN Resolution which recognises the Caribbean as a significant biodiversity hotspot, and calls for increased regional and international action to halt biodiversity loss. “The results of these Red List assessments will help identify freshwater conservation priorities that can address the objectives of that IUCN Resolution,” Dr. León suggests.


IUCN Freshwater Fish Specialist Group

Rivercide: live-streamed documentary investigates river pollution in England and Wales

July 16, 2021

Earlier this week a new live-streamed documentary, Rivercide, was broadcast. The documentary, presented by environmentalist George Monbiot, investigates the impacts of pollution on British rivers.

“Our rivers should be beautiful, complex ecosystems,” says Monbiot. “But on our watch, they’ve become open sewers, poisoned by sewage and farm slurry. They’re dying before our eyes.”

Broadcast live from the banks of the River Wye, which runs between England and Wales, Rivercide features interviews with conservation scientists, wild swimmers, anglers, politicians, local residents and citizen scientists to document the ecological impacts of rising agricultural and urban pollution in the river catchment.

“Last year raw sewage was released into English rivers over 400,000 times, for over 3 million hours,” says Monbiot. “The Mogden Sewage Treatment Works in Twickenham spewed 3.5 billion litres of raw sewage into the Thames last year. On one day in October, they spilled over a billion litres, which is the equivalent of over 400 Olympic-sized swimming pools of raw sewage.

“As well as releasing faecal bacteria and other nasty chemicals into our water, untreated sewage includes pollution in the form of wet wipes and sanitary towels, leading to build-up of microplastics. And yet, nationally, sewage isn’t even the biggest polluter of our rivers. Agriculture is the sector responsible for most river pollution,” says Monbiot.

The documentary highlights how the regulatory bodies responsible for environmental regulation in rivers in England and Wales – the Environment Agency and Natural Resources Wales, respectively – have been subject to significant budget cuts in the last decade.

“Rivercide shows how the agencies charged with protecting our rivers have been progressively under-funded and under-resourced and are failing to adequately monitor water quality and enforce action against polluters,” says Monbiot. “For example, at current rates, the average farm can expect to be inspected by the Environment Agency once every 263 years.

“Rivercide investigates who’s polluting our rivers and why we’re allowing them to get away with it. We examine acute pollution incidents too – for example the tragic pollution of the Afon Llynfi in Wales which occurred last July, killing over 10,000 fish,” says Monbiot.

The Rivercide Emergency Rescue Plan. Image: Rivercide.

The documentary, produced on a limited Kickstarter-supported budget using mobile phone and drone streaming techniques, also features contributions from singer Charlotte Church and poets Owen Sheers and Benjamin Zephaniah.

“Rivercide is the antithesis of those deathly Zoom calls we’ve all had to endure this last year,” says award-winning director Franny Armstrong. “Yes, it’s using the same technology, but in spirit it’s the anarchic offspring of Springwatch and Challenge Anneka.

“You’d be hard pressed to find a single person in this country who actively wants dirty rivers. And yet every single one of the rivers, lakes and streams that’s monitored in England is now polluted. How can that be? That’s the mystery which Rivercide is setting out to solve – live, in real time.”

The documentary is produced in support of the River Action organisation’s ‘Give Us Back Our Rivers’ campaign, which calls for a doubling of funding for the Environment Agency in England and Natural Resources Wales in Wales.

“It’s madness that we live in a time of cars that drive themselves and fitbits for dogs and yet we put raw sewage into our rivers and allow 20 million chickens to poo into a single river catchment,” says Armstrong. “After a year of lockdown, we’re now a nation of wild swimmers and nature lovers – just imagine how much more fun we’d all be having if our rivers were safe and healthy again, both for wildlife and for people?”


Rivercide website

Give us Back our Rivers campaign

An eBioAtlas of global freshwater biodiversity

July 1, 2021
Water sampling for eDNA using the eBioAtlas test kits. Image: eBioAtlas

Freshwater habitats are vital for biodiversity and human communities around the world. Covering only 1% of Earth’s surface, freshwaters support 10% of all known animals, 30% of vertebrates and over 50% of fish. However, as a series of recent reports have documented, freshwaters are amongst the world’s most threatened habitats.

At present, freshwater conservation and restoration projects are limited in many parts of the world by limited scientific knowledge about the status and distribution of species. Such incomplete mapping of freshwater biodiversity – and the threats it faces – makes effective conservation funding, management and policy difficult.

A major new project seeks to address this issue through the use of environmental DNA (or eDNA) techniques. Together, the International Union for Conservation of Nature (IUCN) and DNA-based monitoring organisation NatureMetrics announced the eBioAtlas project earlier this month.

The project will supply easy-to-use water pump sampling kits to conservationists and citizen scientists in areas of critical freshwater conservation importance, including the Amazon, Ganges, Mekong Delta, and the Niger Delta. Their aim is to collect 30,000 water samples over the first three years, which can then be analysed for eDNA – the traces of DNA left in water by species of fish, birds, amphibians and land animals.

The eDNA technique thus allows conservationists to detect the presence of freshwater biodiversity which might otherwise be difficult or expensive to monitor. As a result, it is intended that the eBioAtlas monitoring will allow local communities to participate in freshwater monitoring over wider areas than ever before.

“eDNA is a game changer because it allows surveys to be done much faster and it has the potential to pick up much more information than through conventional sampling,” says Dr. Will Darwall, Head of IUCN’s Freshwater Biodiversity Unit.

“A third of the world’s freshwater fish are threatened. If nothing changes in the way we manage freshwater environments these species are headed for extinction. We need a full-scale bio-blitz using eDNA to rapidly get new and updated information about where freshwater fish live all over the world so we can bring it into the mainstream of conservation and environmental management and policy efforts,” Dr. Darwall states.

The eBioAtlas monitoring work will result in a freshwater biodiversity database freely available for research and conservation. It is intended that the results will inform species assessments on the IUCN Red List of Threatened Species, and identify sites in need of protection as Key Biodiversity Areas.

“eDNA’s usefulness will only grow over time, as more and more data become available to allow comparisons and cross-referencing between scientists around the world,” says Angelique Todd, Senior Programme Manager, West and Central Africa at eBioAtlas partner Flora & Fauna International.

“We face a biodiversity crisis and we’ve been running blind,” says Dr. Kat Bruce, NatureMetrics founder and Chief Technology Officer. “We know we have to act to protect threatened species and their habitats, but the lack of data makes it hard to set tangible targets and monitor progress, or to incentivise businesses and governments to take meaningful action. We end up spinning in circles and going nowhere, while the loss of nature continues to accelerate.

“eDNA is totally transformative. It’s a tool we can put in the hands of ordinary people all over the world to capture biodiversity data at a previously unthinkable scale – and from those simple water samples, we will generate the knowledge base that can underpin effective action for the protection and restoration of nature. Nothing is more important.”


eBioAtlas website

High levels of pesticide pollution found in streams in German agricultural landscapes

June 17, 2021
Pesticides from intensive agriculture are present at high concentrations in streams across Germany. Image: amberandclint | Flickr Creative Commons

The use of pesticides to control insects, fungi and plants which threaten agricultural production has soared globally in recent decades. One recent study suggests that that around one-third of the planet’s agricultural land is at ‘high risk’ of pesticide pollution, and that aquatic ecosystems are particularly vulnerable to the harmful effects of pesticide run-off.

The 2019 UN Global Environment Outlook states that food production is a major driver of global biodiversity loss, and a significant pollution source for aquatic environments. This is particularly the case where intensified agricultural practices are heavily reliant on chemical pesticides and fertilisers.

A newly-published study suggests that small streams in agricultural landscapes across Germany are heavily polluted with pesticides, causing significant effects on aquatic biodiversity. Over two years, a team of scientists led by the Helmholtz Centre for Environmental Research (UFZ) studied pesticide contamination at more than 100 monitoring sites on streams flowing through agricultural lowland regions across Germany.

The research team found that government ‘safe’ thresholds for pesticides were exceeded in over 80% of the streams. In 18% of the streams, these thresholds were exceeded by more than ten different pesticides, showing the ‘cocktail’ of chemical stressors the small stream ecosystems are subject to.

“We have detected a significantly higher pesticide load in small water bodies than we originally expected,” says Professor Matthias Liess, ecotoxicologist at the UFZ and coordinator of the small water monitoring project.

In some streams the pesticide loads were significantly higher than government thresholds. In three water bodies, the insecticide thiacloprid was detected at concentrations over one hundred times the threshold. In twenty-seven streams, the insecticides clothianidin, methiocarb, and fipronil, as well as herbicides such as terbuthylazine, nicosulfuron, and lenacil, exceeded the threshold 10 to 100-fold.

Researchers studied pesticide contamination in streams in German agricultural landscapes for two years.
Image: André Künzelmann / UFZ

The researchers’ detailed datasets revealed that pesticides negatively impact stream insect communities at much lower concentrations than previously assumed in government risk assessments. “For sensitive insect species, the pesticide concentration in the small lowland streams is the most relevant factor that determines their survival,” says Professor Liess. “In contrast, other environmental problems such as watercourse expansion, oxygen deficiency, and excessive nutrient content are less important. For the first time this study allows a ranking of environmental problems.”

The study suggests that German government thresholds for the management of aquatic pesticide pollution are insufficient for protecting invertebrate communities. The researchers suggest that this is because, until now, the ecological risk posed by pesticides has been predicted using laboratory studies, artificial ecosystems and computer simulations.

“In addition to pesticides, many other stressors act on organisms in the ecosystem,” states Professor Liess. “These make them much more sensitive to pesticides. Natural stressors such as predation pressure or competition between species are not sufficiently taken into account in the risk assessment. But these obvious problems often go unnoticed because the degree of pesticide contamination and the effect of this have not been validated in the field – neither in Germany nor in other countries.”

The scientists found that the type of sampling method use significantly influenced their measurements of pesticide concentrations. Scoop samples of water are standard for water quality monitoring under the EU Water Framework Directive. However, the scientists found that ‘event samples’, which automatically collect water samples after rainfall, provide much higher concentrations of pesticides entering the stream ecosystems.

“The event sample provides much more realistic results because the pesticides enter the water bodies as a result of the increased surface run-off from the field, especially during rain,” says Professor Liess. “In order to realistically depict the water pollution, samples must therefore be taken after rainfall events. That’s why we need an official regular environmental monitoring to be able to assess the amount and the effects of pesticides.”

The study has significant implications for the management of aquatic ecosystems within agricultural landscapes in Germany. ”We are still using pesticides that were approved many years ago based on an outdated risk assessment,” argues Professor Liess. “This must therefore change as soon as possible. Only in this way can we preserve the biodiversity in our waters and with it the services that these biotic communities provide for our ecosystems.”


Liess, M., Liebmann, L., Vormeier, P., Weisner, O., Altenburger, R., Borchardt, D., Brack, W., Chatzinotas, A., Escher, B., Foit, K. and Gunold, R., (2021). “Pesticides are the dominant stressors for vulnerable insects in lowland streams.” Water Research, (open-access until 29 July 2021)

PONDERFUL is launched: pond ecosystems for resilient landscapes in a changing climate

June 4, 2021
The new PONDERFUL project aims to champion and support the value of pond ecosystems. Image: PONDERFUL

Next week marks the launch of the new PONDERFUL project. The EU Horizon 2020 funded project will explore the role of ponds in protecting freshwater biodiversity, delivering ecosystem services, and helping mitigate climate change impacts.

Ponds are increasingly recognised as vital habitats for freshwater biodiversity, and important biogeochemical hotspots. As a result, they are responsible for providing a range of vital ecosystem services. However, ponds and other small freshwaters have long been overlooked in aquatic research.

This means that they are largely under-valued in environmental management and policy. In Europe, for example, the Water Framework Directive almost completely ignores ponds in its freshwater policy guidance.

“PONDERFUL is the largest EU-funded project to date on the role of ponds in protecting biodiversity and delivering ecosystem services, specifically to mitigate and adapt to the impacts of climate change,” says Professor Sandra Brucet, who leads the PONDERFUL project.

”We expect to create unique new datasets linking freshwater biodiversity to the delivery of ecosystem services, to help us give better advice to land and water managers working to protect freshwater biodiversity and deliver vital ecosystem services,” continues Professor Brucet. “This fundamental new data will particularly help us better define the relationship between aquatic biodiversity and the production of greenhouse gases, a major concern in the management of aquatic habitats.”

Ponds have long been overlooked in scientific research and undervalued in environmental policy. Image: PONDERFUL

The PONDERFUL project involves 18 partners from 11 states – including Uruguay in South America – forming what is likely to be the largest-ever pond research project. The project is designed to support IPBES and other biodiversity strategies and conventions to better protect freshwater biodiversity, which, as this blog has documented, is a severely threatened component of global biodiversity.

“We’ve brought together a strong international team of aquatic ecologists, geochemists, modellers, landscape conservationists and social scientists, and will collaborate closely with relevant stakeholders,” says Professor Brucet. “This will help provide new guidance to policy makers and practitioners to help them maximise the enormous practical benefits to be gained from working with ponds.”

Ponds are known to be freshwater hotspots, but new research shows they can help landscape-wide recovery too. Many of the existing pond ecosystem studies have taken place in Europe, and there is a significant need for additional research, both across the continent and globally.

“We think PONDERFUL could create a step change in interest amongst both researchers and practitioners in the role of these small, but critical, habitats,” says Dr Jeremy Biggs, from the UK Freshwater Habitats Trust, which has championed the importance of ponds for 30 years. “There may be as many as 3 billion ponds on the planet, and their importance is out of all proportion to their size. Although often regarded as ‘the humble pond’, we regard them as frankly miraculous, hence our adoption of the neat acronym ‘PONDERFUL!’”

PONDERFUL will bring together researchers both from across Europe, and globally. Image: PONDERFUL

The PONDERFUL online launch will mark the start of collaborations between over 500 researchers and practitioners from 39 countries in Europe. The launch, which will introduce the value and importance of pond ecosystems, will also promote the Ramsar Convention’s 2018 Resolution XIII.21 on the ‘conservation and management of small wetlands’.

“In the UN Decade on Ecosystem Restoration, with the protection, creation and management of ponds we have perhaps the most achievable, deliverable and impactful single water management programme we find to protect freshwater biodiversity,” says Dr Biggs. “We just need to make people aware of the enormous benefits to be associated with these ancient, natural and rich freshwater ecosystems.”

The PONDERFUL online launch takes place from 1500hrs (CEST) on Thursday 10th June 2021. Attendance is free, sign up here.

Developing MEASURES for reconnecting migratory fish habitats in the Danube basin

May 28, 2021
The Danube at Mitterhaufen, Austria. The MEASURES project aimed to restore ecological river corridors across the Danube basin. Image: MEASURES

In 2019 we featured a major new freshwater project, MEASURES, founded to manage and restore ecological riverine corridors in the Danube River basins. Funded by the EU as part of the Danube Transnational Programme, MEASURES aimed to improve habitat quality and connectivity along the Danube in order to support populations of six threatened sturgeon species, as well as other migratory fish and wider aquatic biodiversity in the basin.

Earlier this month, the project held its final conference, bringing together participants from diverse fields interested in the conservation and restoration of the Danube basin.

“The MEASURES final conference was held to disseminate the key results of the project, and to present linkages with other initiatives dealing with revitalisation and ecological continuity of the Danube and its tributaries,” says project manager Silke Drexler. “Although the conference took place virtually, it was of high interest to a broad group of stakeholders. The participants included scientists, experts from NGOs, practitioners from private companies, and from governmental agencies. The vibrant discussions addressed topics such as eDNA, broodstock collection, science-policy implementation and future projects for a vital eco-corridor along the Danube.”

The MEASURES project had four key areas of activity, each accompanied by a fact-sheet. First, the project created a series of ‘Infosystem Eco-Corridors’, based on the establishment of a network of Danube stakeholders across 8 partner countries. A new MEASURES Information System (MIS) was developed, hosting online information on migratory fish and habitats in the Danube basin, linked to the Freshwater Information Platform and the Danube Future Knowledge Base. (fact-sheet)

Second, project researchers undertook fieldwork and data collection to map potential sturgeon habitats along the Danube and its tributaries. This resulted in a publication, the Danube Migratory Fish Habitat Manual, which detailed key sturgeon habitats in the basin, and the methods used to map them. The habitat mapping activities in MEASURES have already contributed to the latest draft of the Danube River Basin Management Plan (fact-sheet)

Third, the project undertook a series of activities to strengthen populations of migratory fish populations in the Danube basin. These included restocking programmes for Russian sturgeon and sterlet, alongside the development of an eDNA sampling method to monitor their populations (activities featured in a recent issue of the World Wildlife Magazine). Project researchers collected gene stocks of sturgeon populations from broodstock and ex-situ samples for future stocking, which is hoped to be undertaken through a follow-up project, LIFE–Boat 4 Sturgeons. (fact-sheet)

Fourth, MEASURES published a new Strategy for the Danube Ecological Corridor, which built on project findings to outline how migratory fish habitats can be restored and reconnected through the Danube basin. The MEASURES Strategy is designed to help support and improve environmental management plans and legislation at different scales throughout the basin, providing suggestions for specific conservation and restoration activities. Details of the Strategy, and the MEASURES eDNA monitoring methods, will be explored in further blog posts over the coming months. (fact-sheet)

Attendees at the virtual MEASURES final conference.

A policy brief entitled Solutions and Barriers – Conservation of Migratory Fish Species and Their Habitats synthesises these activities, and calls for the establishment of a Regional Water Council on the Mura and Sava rivers in order to better support local, national and international cooperation. The MEASURES website features a wealth of information about the Danube basin and its migratory fish species, including an archive of newsletters, images and a 2021 calendar.

“The MEASURES project involved 24 partners from 13 countries cooperating to secure threatened riverine fish species,” says project co-ordinator Thomas Hein. “Our three year cooperation allowed major steps in gaining new knowledge on migratory fish in the Danube River Basin and transferring these insights into practice. MEASURES is an excellent example of cross-sectoral international collaboration to address an important aspect of freshwater biodiversity.”


MEASURES website
MEASURES Information System (MIS)

Lake heatwaves to become ‘hotter and longer’ by the end of the century

May 20, 2021
Lake Isabella, California, under drought conditions. New research suggests that heatwaves will become increasingly common influences on global lake ecosystems in coming decades. Image: Don Barrett | Flickr Creative Commons

Lake ecosystems across the world are increasingly vulnerable to water temperature increases caused by ongoing climatic change. Species of plants, fish and animals that live in lakes are particularly susceptible to the effects of climate change, because they have often adapted to local conditions and lack the ability to migrate away from a changing habitat.

As recent research has shown, warming water temperatures can interact with other environmental stressors such as nutrient pollution to cause significant ecological issues like eutrophic algal blooms. However, until recently, little was known about lake heatwaves, particularly how and where they will occur in the future.

IntEL, a newly-completed EU-funded research project, has recently provided the first detailed study of lake ecosystem responses to warming temperatures under predicted future climate change. “Quantifying and understanding these changes is crucial if we are to try to mitigate these impacts,” says Prof. Eleanor Jennings, IntEL project coordinator. “In addition, the ability to describe and quantify these effects can contribute to the weight of evidence that the global population must reduce their output of greenhouse gases”

Writing in the Nature journal, IntEL researchers provide a new metric to quantify lake heatwaves, produced through computer modelling work across hundreds of sites globally. The research team show that lake heatwaves are likely to become “longer and hotter” by the end of the 21st Century. Significantly, they suggest that some lakes will reach a permanent heatwave state extended over multiple years.

“Lake heatwaves are defined as periods of anomalous lake surface temperatures, when temperatures exceed historical average conditions for that time of year,” says IntEL research fellow Dr. Iestyn Woolway. “The metric developed can be applied to any lake on Earth but, in this study, we focused solely on lakes using satellite observations.”

The researchers suggest that by the end of the 21st Century, many global lakes will have increased water temperatures as a result of more regular heatwave events. Heatwaves, in many lakes, will thus cease to be extreme events, and instead become part of ‘normal’ ecosystem conditions.

The project findings have significant implications for freshwater life in lakes. The researchers highlight the potential for ecosystem shifts as a result of decreased ice cover, decreased water oxygen levels, and increased cyanobacteria blooms in different lakes.

Similarly, they note the potential for warming water temperatures to alter the mixing and cycling of thermal layers and nutrients in some lakes. The likely result is the alteration, or loss, of habitat for biodiversity in many lakes, potentially causing the breakdown of food webs. Species already at the upper limit of their temperature tolerance, and those unable to migrate to more favourable habitats, may become locally extinct.

The researchers write, “These complex inter-actions are hard to forecast, but the extreme heatwave in the summer of 2003 in central Europe illustrated the range of effects that might be expected, including increased thermal stability and hypolimnetic oxygen depletion, production of cyanobacterial blooms and a regime shift from pelagic to benthic productivity.”

In other words, whilst we can expect lake heatwaves to increase in intensity and duration across the world in the coming decades, it is difficult to accurately forecast the resulting ecological impacts. This uncertainty provides a convincing argument both for transitioning to low-carbon economies to minimise future climatic change, and in building climate resilience into freshwater systems through habitat conservation and restoration work.

The IntEL researchers are not finished with their work, however. “Future work will investigate the influence of climate change on a host of other essential lake properties, including the phenology of lake stratification – the vertical layering that exists in many lakes in summer – and the influence of warming on greenhouse gas production in lakes,” says Prof. Jennings.


Woolway, R.I., Jennings, E., Shatwell, T. et al. Lake heatwaves under climate change. Nature 589, 402–407 (2021).

‘Plastic is everywhere’: microplastics found in 1950s freshwater fish specimens

May 7, 2021
Specimens of sand shiner fish in the Field Museum’s collections collected in 1972, 1953, and 1907. Image: Kate Golembiewski, Field Museum

Freshwater fish have been swallowing microplastics since at least the 1950s, according to a newly published study. Microplastics – tiny threads and fragments of plastic resulting from the breakdown of waste, clothing and cosmetics – are an increasingly important topic of environmental concern, having been found in deep oceans, on high mountain tops, and even in the atmosphere.

A team of researchers examined preserved freshwater fish specimens from the Chicagoland region, USA, kept in the Field Museum collection. Four species in the museum collection – largemouth bass, channel catfish, sand shiners, and round gobies – had specimen records dating back to 1900. The team’s analysis shows that once plastic manufacturing became industrialised in the 1950s, microplastics began to significantly accumulate in the fishes’ bodies.

“For the last 10 or 15 years it’s kind of been in the public consciousness that there’s a problem with plastic in the water. But really, organisms have probably been exposed to plastic litter since plastic was invented, and we don’t know what that historical context looks like,” says Dr. Tim Hoellein, associate professor of biology at Loyola University Chicago and the corresponding author of the new study, published in the Ecological Applications journal. “Looking at museum specimens is essentially a way we can go back in time.”

Working with Dr. Caleb McMahan, an ichthylogist at the Field Museum, Hoellein and graduate student Loren Hou examined the preserved fish specimens for evidence of microplastics. “We would take these jars full of fish and find specimens that were sort of average, not the biggest or the smallest, and then we used scalpels and tweezers to dissect out the digestive tracts,” says Hou, lead author of the new study. “We tried to get at least five specimens per decade.”

Hou used hydrogen peroxide to look for microplastics in the preserved fishes’ digestive tracts. “It bubbles and fizzes and breaks up all the organic matter, but plastic is resistant to the process,” she says. Under the microscope, microplastics more than half-a-century old were revealed. ”We look at the shape of these little pieces. If the edges are frayed, it’s often organic material, but if it’s really smooth, then it’s most likely microplastic,” says Hou.

“We found that the load of microplastics in the guts of these fishes have basically gone up with the levels of plastic production,” says McMahan. “It’s the same pattern of what they’re finding in marine sediments, it follows the general trend that plastic is everywhere.”

The research team point to a key cause of microplastics discovered in the fish specimens: fabrics. Many of the microplastics they discovered were thread-like and likely to have been washed out of clothing. “It’s plastic on your back, and that’s just not the way that we’ve been thinking about it,” says Hoellein. “So even just thinking about it is a step forward in addressing our purchases and our responsibility.”

A portion of the Field Museum’s fish collections, which contain two million specimens and are primarily housed in underground storage in the museum’s Collection Resource Center. Image: Kate Golembiewski, Field Museum

The researchers cannot say for sure how microplastic ingestion affected the fish specimens studies, but it is likely to have caused physiological effects. “When you look at the effects of microplastic ingestion, especially long term effects, for organisms such as fish, it causes digestive tract changes, and it also causes increased stress in these organisms,” says Hou.

Their study is published on the heels of the claim that scientific breakthroughs could facilitate the use of bacterial biofilms to trap and recover microplastics from rivers, lakes and seas. Speaking to the Microbiology Society’s Annual Conference at the end of April, Yang Liu, a researcher at Hong Kong Polytechnic University, and colleagues are hopeful that a naturally occurring bacteria can be used to colonise and aggregate microplastics in the environment, causing them to sink for removal.

Liu outlines why microplastic is such an important environmental issue, “Microplastics are not easily bio-degradable, where they retain in the ecosystems for prolonged durations. This results in the uptake of microplastics by organisms, leading to transfer and retention of microplastics down the food chain.

“Due to their huge surface area and adsorption capacity, microplastics can adsorb toxic pollutants, such as pesticides, heavy metals, and drug residues at high concentrations. This leads to biological and chemical toxicity to organisms in the ecosystems and humans after prolonged unintended consumption of such microplastics. Moreover, microplastics are also difficult to remove in wastewater plants, resulting in their undesired release into the environment,” Liu states. Liu and colleagues hope that their nascent technique will eventually be used in wastewater treatment plants to stop microplastics travelling into the wider environment.

For now, the museum specimen study by Hou and colleagues reminds us that for all its contemporary interest, microplastic pollution is nothing new. Hou and colleagues hope their study will act as a ‘wake-up call’ for the public and politicians to take notice of the widespread and pervasive nature of microplastic pollution in our aquatic environments.


Loren Hou et al (2021), A fish tale: a century of museum specimens reveal increasing microplastic concentrations in freshwater fish, Ecological Applications. DOI: 10.1002/eap.2320

One of Europe’s last wild rivers: biodiversity and hydropower on the Vjosa River

April 23, 2021
Braided river channel on the Vjosa River, Albania. Image: Gregor Subic

The Vjosa River in Albania is often termed one of ‘Europe’s last wild rivers’. It flows unobstructed by dams and hydropower plants along its 270km course through deep canyons, braided channels and wide meanders to the Adriatic Sea. The fact that the Vjosa River’s course – and that of its tributaries – is intact makes it a unique river system in Europe.

In recent years, scientists and campaign groups have undertaken a series of research projects and public events in order to highlight the Vjosa’s diverse ecosystems, and the biodiversity they support. This work has been carried out in response to the increasing threat of hydropower construction in the Vjosa catchment. Whilst the Vjosa is bordered by a number of protected areas, it has little environmental protection, and as a result there are currently 38 hydropower plants planned for construction within its catchment. However, up until recently, there has been very little data available on the Vjosa’s ecological and fluvial diversity, meaning environmental campaigners have had scant scientific evidence available to support their work.

A newly released report provides the first ‘baseline’ study of the Vjosa’s ecosystems and biodiversity, stating that the river is an extremely rare site with valuable habitats supporting numerous protected and endangered species. A team of scientists – co-ordinated by Dr. Paul Meulenbroek at the University of Natural Resources and Life Sciences, Institute of Hydrobiology and Aquatic Ecosystem Management (IHG) in Vienna – documented over 1100 plant and animal species, many of which are protected under national and international law. Their study suggests that the Vjosa is thus one of the few remaining ‘reference’ sites for dynamic floodplains in Europe, characterised by its ‘near-natural’ status.

The report authors use their findings to make a series of objections to the proposed Kalivaç hydropower plant. The Kalivaç project was originally approved in 1997, but its construction – close to the town of Tepelena – has never been finished, and the river still flows uninterrupted. However, plans for the project’s construction continue, with a proposed 43 metre-high rockfill dam across the river which would create a 16km² reservoir as a means of generating hydropower electricity.

The authors make three main objections to construction. First, they argue that the Kalivaç project would lead to the complete and irretrievable loss of more than 1000 hectares of natural and near-natural river and floodplain landscape. They suggest that such “destruction of one of the greatest wild river landscapes in Europe” would cause local decreases in around 40% of all species, and block over 800km of the river network to migratory fish.

Second, the authors suggest that the Kalivaç project poses a significant local biodiversity extinction risk, and it is expected to destroy around 870 hectares of habitat listed by the EU Habitat Directive. As such, the authors state that the project poses a contravention of a number of European and international laws and conventions, also including the IUCN Red List, the Bern Convention, and Birds Directive.

Third, the report states that the Kalivaç reservoir would fill with sediment within 60 years, leading to an ongoing loss in energy potential each year, and requiring significant dredging management. The authors suggest that such sedimentation would pose high economic costs to hydropower managers, cause ongoing ecological losses, and limit the potential of the Vjosa catchment to attract eco-tourists.

Image: Sébastien Champeaux

The report is released only weeks after environmental activists staged public interventions in Paris, Brussels, Berlin and Tirana, where fabric spelling out ‘Vjosa National Park Now’ was draped in the foreground of heritage monuments. The interventions were coordinated by the Save the Blue Heart of Europe campaign as a means of highlighting the need to designate the Vjosa as Europe’s first Wild River National Park. In September 2020, Albanian Prime Minister Edi Rama stated his intention to protect the Vjosa, but there has been little subsequent progress, and the current environmental protection designations offer only minimal protection from future hydropower construction.

The authors of the new report conclude by outlining the urgent need for significant new environmental protections for the Vjosa catchment. They write, “The fauna and flora of this highly dynamic river represent the last inhabitants of a dwindling river refuge. Their survival depends on well-planned management of both the catchment and the surrounding areas. As a model for restoration measures, and a cradle of biodiversity and natural heritage, this river and its community are too important to be lost.”


Meulenbroek, P., Egger, G., Trautner, J., Drescher, A., Randl, M., Hammerschmied, U., Wilfling O., Schabuss, M., Zornig, H., Graf, W. (2020) The river Vjosa – A baseline survey on biodiversity, potential impacts, and legal framework for hydropower development. pp. 180. DOI: 10.5281/zenodo.4139640

Catch the drift: river fish and birds rely on mobile invertebrate prey

April 9, 2021
Dipper. Image: Charles Tyler

New research shows how salmon, trout and river birds in Welsh upland rivers rely on invertebrate prey with specific ‘drifting’ behaviours for their food sources.

The open-access study, led by Cardiff University, found that iconic predatory fishes, such as the brown trout and Atlantic salmon, and birds, such as the Eurasian dipper and grey wagtail, are most abundant where invertebrate prey have certain characteristics. Specifically, all the predators were most numerous where mobile ‘drifting’ prey such as mayflies occurred abundantly in fast flowing habitats. These traits also predicted predator populations more effectively than overall prey variety or abundance.

The team from Cardiff, Cambridge and Roehampton Universities, the British Trust for Ornithology and Imperial College of London assessed predator numbers along Welsh upland rivers in relation to invertebrate numbers and trait composition. Researchers were also interested in assessing whether these specific aspects of biodiversity were important elements in river ecosystem services such as economic gains from angling or cultural values.

“Our work demonstrates the importance of river invertebrates – the ‘hidden biodiversity’ that is often underappreciated by society – in sustaining well-known and iconic river predators” said Dr Cayetano Gutiérrez-Cánovas, lead author of the study. “Roughly half of European rivers currently fail against EU targets for ecological status which is likely to reduce invertebrate numbers and prey availability for freshwater predators – yet this link is seldom made or recognised by those charged with managing river ecosystems”, states Gutiérrez.

Grey wagtail. Image: Charles Tyler

Co-author of the study, Prof Steve Ormerod added:

“We’ve known for some time that predators specialise on certain prey types – for example invertebrates of the correct size for adult birds to feed their young, or prey rich in calcium for egg formation. But this new study shows us how several river predators converge on accessible, drifting prey in faster flows. This raises intriguing questions about how they divide up these prey resources, but also how we can manage and restore rivers to ensure that these and other predators can co-exist in numbers.”

The findings of this study might go some way to explaining dramatic declines of freshwater vertebrates by showing how reliance on river invertebrates can make aquatic predators vulnerable to ongoing river degradation or the transfer of toxicants to apex predators.

Amidst growing concerns about the plight of freshwater vertebrates, the study illustrates how healthy invertebrate populations benefit predators while also helping society. Invertebrate-dependent salmonids, such as trout and salmon, are highly ranked in recreational fishing that boosts visitor numbers, employment and local economies. In addition, greater invertebrate availability also benefits bird conservation, with all its associated cultural value and opportunities for ecotourism.

This research was funded by the NERC DURESS investigation into the benefits that upland rivers provide to society as well as the EU MARS study of multiple stressors on freshwater ecosystems.


Gutiérrez‐Cánovas, C., Worthington, T. A., Jâms, I. B., Noble, D. G., Perkins, D. M., Vaughan, I. P., Woodward, G., Ormerod, S.J. & Durance, I. (2021). Populations of high‐value predators reflect the traits of their prey. Ecography. (open-access)