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Once very abundant in European rivers, the eel population dramatically declined by more than 90% so that eels are now considered as critically endangered. The causes of this rapid decline are unknown. Our recent data point to a new possible contributing cause: aluminium. We need your support for analysing aluminium content of eel ear bones (otoliths) collected over the last 100 years as to validate this hypothesis. If proved true, this could serve as basis for developing effective means to help restoring the eel population.
L’anguille européenne, jadis très abondante dans nos rivières est menacée d’extinction. Ce projet vise à tester une nouvelle hypothèse originale basée sur une découverte récente, et associant la disparition des anguilles à l’acidification des rivières par les pluies acides. L’utilisation de technologies de pointe permettra de révéler l’impact des pluies acides sur des échantillons collectés il y a 100 ans. Nous faisons un appel aux sponsors et au public (crowdfunding) afin d’analyser un grand nombre d’échantillons. Si l’hypothèse est validée, nous pourrons développer des stratégies pour accélérer la restauration de la population de ces poissons abyssaux venus s’établir dans nos rivières.
(Opens 7 November 2016, Flexible Funding - This campaign will keep all funds raised)
The first phase of this campaign has now closed. If you would like to receive updates about the research please register and we'll keep you informed about our progress and upcoming campaign.
Reference: Projet Anguilles, Account: IBAN BE29 2710 3664 0164 BIC : GEBABEBB
This appeal is supported by:
A rapid decline in European eel populations occurred in the early 1980’s
Eels (Anguilla anguilla) originate in deep waters from the Sargasso Sea, in the middle of the Atlantic Ocean. From there, larvae will drift for months towards European coasts and enter estuaries. The so-called elvers will establish themselves in rivers and coastal areas for 10 to 20 years. At that time, eels have stored large amounts of energy into their tissues will start a 6000-km migration back to the Sargasso Sea where they supposedly reproduce and thereafter die.
For centuries, eels from rivers and the huge quantities of elvers reaching estuaries each year provided food and livelihood to many Europeans. Until the decline started. First signs of stock reduction occurred in the early 80’s and the decline progressed at very high speed. Similar collapses took place among other eel species in Asia and North America. Since then, researchers have attempted to link the collapse to different human and environmental causes. Up to now, no single cause could explain both the timing and high speed of the declining stocks.
A new hypothesis: Could the decline in eel numbers be due to the higher aluminium levels in river systems?
Recently, we detected very high amounts of aluminium (Al) in tissues of eels collected in Belgium. Aluminium is toxic to fish, mainly because it binds to gills and affects the capability of the animal to regulate its water and salt composition. This is particularly important in animals moving between fresh and seawater, as eels do.
Aluminium is normally poorly available to organisms due to its sequestration as silicates in soils, and so it is normally absent from rivers and ponds. Unless soil becomes acidic as acidity solubilises silicates. And this is exactly what happened decades ago when rain became acidic due to air pollution.
We therefore propose a new hypothesis for a contributing factor explaining the sudden collapse of eel population. This new scenario suggests that acid rain released aluminium from soils into rivers, allowing the toxic metal to reach eel gills and reduce their capability to regulate their salt and water body contents. The high mortality of mature adults upon reaching the ocean could have led to the rapid decrease of eel larvae reaching European coasts.
To test this hypothesis, we need to study aluminium contamination in eels
We have access to a collection of 300.000 ear bones (otoliths) collected on Dutch eels since 1920. Thanks to very sophisticated analytical techniques, aluminium will be quantified in otoliths, giving us information on the abundance of the metals in the fish tissues.
The results will allow us to determine the evolution of aluminium contamination in eels between 1920 and now. If we can demonstrate a link between aluminium contamination and the evolution of eel stocks, we may then propose a new strategy for restoring eel stocks through aluminium decontamination of rivers and eels before their return to the ocean.
Otoliths (ear-bones) as time-machine
Hypotheses are valuable only when they can be experimentally challenged. In this case, it would require proving that aluminium contaminated eels 50 years ago to such an extent that it caused important mortality. This seems impossible. Yet we think we have found one way to prove this. Fish have a peculiarity in their inner ears: they contain small clusters of limestone called otoliths. These otoliths , which are important for the fish balance, grow continuously up to 3 mm diameter, forming new circles of minerals every year, similarly to the rings found in trees. During their growth, metals present in fish tissue are trapped within the limestone. Thanks to very sophisticated analytical techniques using a laser (LA-ICP-MS, see below), these trapped metals can be quantified, giving us information on the abundance of the metals in the fish tissues.
Otoliths grow continuously with the fish and they will provide us with information on the seasonal variations of aluminium contamination
This is particularly important as eel migration takes place in the autumn and it is therefore critical to measure the abundance of aluminium in eels at the onset of their migration into the ocean.
Luckily, Dutch researchers have collected otoliths of eels caught in the IJsselmeer Lake since 1920’s. This historical otolith collection counts more that 200,000 otoliths, a fantastic tissue bank for testing our hypothesis.
We have set-up a Pan-European consortium of eel experts from seven laboratories that will allow the analysis of eel otoliths collected over the last half century
Testing our hypothesis requires that many otoliths are analysed. Indeed, variations in aluminium concentration will depend on the life history of eels, their size and other genetical and physiological parameters. To detect a trend despite individual variations requires acquisition of data from many specimens.
One simple otolith analysis giving us mean aluminium concentration costs 50 Euros
A more extended analysis of an otolith, which provides a full map of aluminium concentration at each moment of the fish life, costs 400 Euros. This last technique will be applied on a more limited set of otoliths as it will give us information on the seasonal variations of aluminium concentration.
Our goal is to carry out simple assays of aluminium in about 400 otoliths from eels of similar size collected from a same location between years 1950 and 2000. Next to this, we will carry out full mapping of aluminium on a set of 20 selected otoliths from eels collected when aluminium reached his highest level.
Eels (Anguilla anguilla) are with no doubt the most mysterious inhabitant of our rivers
Eggs hatch in deep waters from the Sargasso Sea, in the middle of the Atlantic Ocean. From there, the leaf-like larvae drift for 6-10 months towards European coasts along the Gulf Stream, and metamorphose into transparent glass eels before entering estuaries. Once in freshwater, pigmentation of the young eels starts. The so-called elvers (sea picture; Credits 123RF/Nicolas Primola) will establish themselves in rivers and estuaries and grow into yellow eels. After 10 to 20 years of storing energy into their muscle, male and female yellow eels will start a 6000-km reproductive migration back to the Sargasso Sea. Their morphology and physiology changes: the now-called silver eels lose their yellow pigmentation, their digestive tract regresses and their eyes enlarge. They also develop the ability to excrete salt through their gills, which is essential to their survival in oceanic salt water.
For centuries, eels from rivers and the huge quantities of elvers reaching estuaries each year provided food and livelihood to many Europeans
The first signs of stock reduction occurred in the early 80’s and the fall progressed at very high speed. Quite surprisingly, similar collapses took place among other eel species in Asia and North America. Since then, researchers have attempted to link the collapse to different human and environmental causes. Could it be the consequence of overfishing of elvers in estuaries or yellow and silver eels in rivers? Is it caused by a parasitic worm infesting adults? Did the construction of dams on rivers fully block their migration? Could it be linked to changes in ocean circulation? Is it related to the high accumulation of organic pesticides and PCBs in river eels? Up to now, even though each of these could have affected stocks, no single cause could explain both the timing and high speed of the declining stocks.
Surprisingly high levels of aluminium were detected in the tissues of Belgian eels
Recently, when studying the contamination of Belgian eels with metals and pesticides, we detected high amounts of aluminium in their tissues. The levels are higher than those of several metals essential to the fish survival! Quite unexpected as aluminium is not supposed to be abundant neither in water nor in eel preys.
Indeed, although aluminium is the third most abundant mineral on Earth after oxygen and silicium, it is poorly available to organisms due to its sequestration as silicates in soils, and so it is normally absent from rivers and ponds. Unless soil becomes acidic as acidity solubilises silicates. And this is exactly what happened decades ago when rain became acidic.
Rain acidification is caused by fossil energy combustion products (SO2,, NOx and NH3) generated mainly by industries (see figure, credits 123RF/Rinder) . It has been first identified in the 70’s and has been a major environmental problem since then, affecting forest (see figure, credits 123RF/anticiclo) and watersheds throughout Europe, North-America and Asia. Acid rain (pH < 5.5) releases Aluminium from soils into rivers and ponds. Once in water, Aluminium can bind to fish gills and enter the blood circulation.
As you certainly know, gills are the breathing organs of fish, homologous to our lungs. Less known is their role in regulating the salt and water content of the animal tissues. In a freshwater fish, gills actively pump salts from the surrounding water into blood, as salts have a tendency to leave the fish tissues. At the opposite, marine species are faced with a huge entry of salt from the salty seawater. In this case, gills will excrete salts into seawater in order to keep tissue salt level constant. This function, essential to the survival of fish, is called osmoregulation.
Gills are essential in migrating eels
Most fish species are adapted to a certain range of salinity and therefore restricted to live in either fresh- or seawater. Few have developed the capability to survive in a wide range of salinity. Together with salmon, eels are one of those. Both species migrate between freshwater and seawater, though they do so in opposite directions. Both are called potamodromous species. As you may understand, such crossing necessitates fully functional osmoregulation capabilities.
Since Aluminium decreases gills’ ability to pump salts, it may prevent the survival of fish attempting to migrate between fresh and seawater. In the case of eels, it could prevent their safe return to the ocean. Interestingly, acid rain and aluminium have been demonstrated to have played a major role in the reduction of salmon stocks by hampering the migration of young smolts back to the sea (Rosseland et al., 2010).
Our hypothesis proposes that acid rain played a major role in the collapse of eel stocks
By washing aluminium into rivers, acid rain allowed the toxic metal to reach eel gills and reduce their osmoregulation capacity, therefore decreasing their survival upon reaching the estuaries. The high mortality of mature adults led to the rapid decrease of eel larvae reaching European coasts.
Our research strategy is based on three complementary approaches:
1. Assessment of past aluminium contamination in European eels. Our goal is to determine whether eels were increasingly subjected to Aluminium during the 20th century. This will be reached through analysis of Aluminium content in eel otoliths collected in the IJsselmeer Lake (Netherlands) between 1920 and now. The measurements will be carried out using Laser Ablation inductively coupled Mass Spectroscopy, a non-destructive method allowing to quantify metals at high sensitivity. Otoliths are irradiated with a high-energy laser that evaporates a tiny portion of the sample. The resulting aerosol is transported in an argon carrier gas stream, decomposed and ionised before to be injected in a mass spectrometer for identification and quantification. Using this technique on otoliths, it is possible to study the kinetics of the contaminants during the life of eels and date the period of maximal exposure. Since such measurements have never been carried out in the past, we performed preliminary tests on eel otoliths. These indicate that Aluminium can be successfully quantified in the otoliths.
This part is the one that is proposed for funding. The two other parts will be carried out aside, as to consolidate the data obtained on otoliths.
2. In vivo determination of the impact of Aluminium exposure on Aluminium deposition in eel otoliths. This will help us determine whether Aluminium abundance in otoliths reflects Aluminium concentration in their environment. Eels purchased from aquaculture will be exposed to realistic environmental doses of Aluminium and the otolith content in Aluminium will be measured. This could validate the approach of using otoliths as memories of Aluminium exposure in eels.
3. Analysis of the susceptibility of eel osmoregulatory processes to Aluminium presence in water. This part will allow us to identify possible osmoregulatory defects in aquaculture-produced eels subjected to Aluminium doses to which they have been exposed. Eels will be exposed to realistic environmental doses such as at point 2 and their ability to face a seawater challenge will be investigated. This will allow us to link Aluminium abundance in otoliths to possible osmoregulation defects in eel.
The lack of understanding for the collapse of eel stocks left researchers and public bodies with no efficient means of action
Identifying the causes for the population decline will empower us to define a strategy for accelerating the recovery of European eel population, and possibly other eel species in North-America and Asia. This could participate to the restoration of the natural ecosystems in European rivers and lakes. Eels are carnivorous and they regulate the population of other fish and invertebrates in ponds and rivers. Their total disappearance could affect the fragile equilibrium of freshwater ecosystems.
Saving eels is important as these fishes have been unlike no other species part of our European history and culture, as reflected by its occurrence in the literature and paintings
While this is obviously related to its importance in gastronomy, it also reflects the mysteries surrounding this snake-like fish. For two thousands years, speculations were expressed on the reproduction of this fish, quite abundant in ponds and rivers but for which no reproduction or larvae had ever been observed. Aristotle believed that eels were sexless and originated from decaying matter by spontaneous generation.
The occurrence of ovaries in eels was only demonstrated in the 18th by the Italian naturalist Antonio Vallisneri! That of testicles took 150 more years... Yet, no one had ever observed eel larvae. Only in 1893, another Italian scientist Gian Battista Grassi realized that individuals of Leptocephalus brevirostris, a leaflike transparent fish species collected in the Atlantic, could metamorphose into glass eels, the early developmental stage of eels. This suggested that eels originated from the ocean, not rivers! Yet the location of their birthplace remained mysterious!
In 1922, the Danish scientist J. Schmidt, sailing from the Mediterranean to the Atlantic noticed a progressive size reduction of glass eels and larvae. He concluded that European eels originate from the Sargasso Sea, and grow as they travel towards Europe, solving a 2000-year long mystery. Further research demonstrated that the now-called leptocephalid larvae drifted for a 6-10 months towards European coasts along the Gulfstream, and that they metamorphose into glass eels before entering estuaries.
A century after solving the mystery surrounding eel origins, we are now faced with its mysterious disappearance
Resolving this new mystery might be more important than finding solutions for previous ones as it might be decisive for saving eels, an important part of our cultural and natural heritage.
This project involves researchers from Belgium, France, Netherlands and Norway who specialise in eels and ecotoxicology.
Claude Belpaire, Ph.D
Research Institute for Nature and Forest (INBO), Brussels.
Claude has 40 years of experience in aquatic ecology. He has been involved in the international management of the European eel for more than 30 years and is member of the EIFAAC-ICES Working Group on Eels. He published numerous papers on the ecology and ecotoxicology of eel, and is well-known for his work on the use of the .eel as indicator organism for environmental quality
Maes, J, Goemans G, Belpaire C.( 2008). Spatial variation and temporal pollution profi les of polychlorinated biphenyls, organochlorine pesticides and heavy metals in European yellow eel (Anguilla anguilla L.) (Flanders, Belgium). Environ. Pollut. 153: 223–237.
Geeraerts C, Belpaire C. (2010). The effects of contaminants in European eel: a review. Ecotoxicology 19: 239–266
Lieven Bervoets, Ph.D.
University of Antwerp, Antwerp
Lieven is a senior researcher within the the Sphere group (Systemic Physiological and Ecotoxicological Research) of the department of Biology of the University of Antwerp, He studied for more than 25 years the bioavailability and effects of micro-pollutants in aquatic and terrestrial organisms.
Mataba G, Verhaert V, Blust R, Bervoets L. (2016). Distribution of Trace Elements in the Aquatic Ecosystem of the Thigithe River and the Fish Labeo victorianus in Tanzania and possible risks for human consumption. Science of the Total Environment, 547: 48-59.
Bervoets L, Knapen D, De Jonge M, Van Campenhout K, Blust R. (2013). Differential hepatic metal and metallothionein levels in three feral fish species along a metal pollution gradient. PLoS ONE 8(3):e60805.
Jean-François Rees, Ph.D., Benjamin Lemaire, Ph.D. and Marie Grisard de la Rochette
Fish physiology and toxicology
University of Louvain, Louvain-la-Neuve
Jean-François and Benjamin are marine biologists specialised in deep sea fish physiology and toxicology. They came to work on eels when they discovered their phylogenetical relationships with deep sea creatures. Jean-François Rees coordinates the Eeluminium Project and supervises Marie’ Master’s thesis.
Bonnineau C, Scaion D, Lemaire B, Belpaire C, Thomé JP, Thonon M, Leermaker M, Gao Y, Debier C, Silvestre F, Kestemont P, Rees JF (2016). Accumulation of neurotoxic organochlorines and trace elements in brain of female European eel (Anguilla anguilla). Environ Toxicol Pharmacol. 45:346-355.
Lemaire B, Debier C, Buc Calderon P, Thome JP, Stegeman J, Mork J, Rees, JF. (2012). Precision-Cut liver slices to investigate responsiveness of Deep-Sea fish to contaminants at high pressure. Environmental Science & Technology, 46(18), 10310-10316.
Christophe Pecheyran, Ph.D. and Hélène Tabouret, Ph.D.
Metal analysis & eel ecotoxicology
Université de Pau et des Pays de l'Adour/ CNRS, Pau.
Hélène and Christophe are research scientists at the French National Center for Scientific Research (CNRS). Christophe is an expert on trace metal speciation and direct analysis of trace elements and their isotopes by laser ablation/ICPMS. He develops new ablations approaches for high repetition rate (HRR) femtosecond laser instrumentation and applications.
Hélène is working on biogenic carbonates, especially fish otolith, as archives of environmental conditions, life history traits and habitat use by temperate and tropical diadromous species (European eel, salmonids, gobioids). She participates to the development of sampling strategies of these archives by femtosecond laser ablation.
Claverie F, Hubert A, Berail S, Donard A, Pointurier F, Pécheyran C. Improving Precision and Accuracy of Isotope Ratios from Short Transient Laser Ablation-Multicollector-Inductively Coupled Plasma Mass Spectrometry Signals: Application to Micrometer-Size Uranium Particles, (2016) Analytical Chemistry, 88 (8), pp. 4375-4382.
Duponchelle F, Pouilly M, Pécheyran C., Hauser M, Renno JF, Panfili J, Darnaude AM, García-Vasquez A, Carvajal-Vallejos F, García-Dávila C, Doria C, Bérail S, Donard A, Sondag F, Santos RV, Nuñez J, Point D, Labonne M, Baras E. (2016) Trans-Amazonian natal homing in giant catfish. Journal of Applied Ecology, . Article in Press.
Tabouret H, Bareille G, Claverie F, Pécheyran C, Prouzet P, Donard OFX (2010). Simultaneous use of Strontium:Calcium and Barium :Calcium in otolith as markers of habitat : application to the European eel (Anguilla anguilla) in the Adour basin. Marine Environmental Research, 70(1), 35-45.
Tabouret H, Tomadin M, Taillebois L, Iida M, Lord C, Pécheyran C, Keith P (2014). Amphidromy and marine larval phase of ancestral gobioids Rhyacichthys guilberti and Protogobius attiti (Teleostei: Rhyacichthyidae). Marine and Freshwater Research, 65(9), 776-783.
Martin de Graaf, Ph.D
Ecology and Fisheries management
Institute for Marine Research (IMARES), Wageningen University, Ijmuiden.
Martin is an expert on ecology and fisheries management. Martin leads the freshwater research group at IMARES, manages the national research program for recreational fisheries and is the project leader for the fish and fisheries research on Saba, Statia and Bonaire.
Tulp I, Keller M, Navez J, Winter HV, de Graaf M, et al. (2013). Connectivity between Migrating and Landlocked Populations of a Diadromous Fish Species Investigated Using Otolith Microchemistry. PLoS ONE 8(7): e69796.
Van De Wolfshaar KE ,Tien N, Winter HV, ,DeGraaf M, Bierman S (2014). A spatial assessment model for European eel (Anguilla anguilla) in a delta, The Netherlands. Knowledge and Management of Aquatic Ecosystems 412, 02
Caroline Durif, PhD
Marine biologist and ecologist
Institute of Marine Research in Norway, Bergen.
Caroline is an eel specialist who developed non-invasive methods to determine when eels are ready for their reproductive migration. She is responsible for eel monitoring at IMR and leads a monitoring program financed by the Directorate of Fisheries. She co-chairs an ICES joint workshop on the effects of contaminants in eel.
Durif C, Browman H, Phillips J, Skiftesvik A, Vollestad L, Stockhausen H. (2013). Magnetic Compass Orientation in the European Eel. PLoS One, 8.
Durif C, Gjøsæter J, Vøllestad L. (2011). Influence of oceanic factors on Anguilla anguilla (L.) over the twentieth century in coastal habitats of the Skagerrak, southern Norway. Proc. R. Soc. B, 278, 464-473.
Eva B. Thorstad, Ph.D.
Norwegian Institute for Nature Research (NINA), Trondheim & University of Tromsø, Norway
Eva B. Thorstad has been working with fish ecology, habitat use and migrations in freshwater, estuaries and marine systems in Norway and several other European, African and Asian countries. She is Norwegian representative at the Joint EIFAAC/ICES Working Group on Eels. She recently worked on eel abundance in acidified rivers and on the impact of aluminium on salmon.
Larsen BM, Hesthagen T, Thorstad E., Diserud O. (2015). Increased abundance of European eel (Anguilla anguilla) in acidified Norwegian rivers after liming. Ecology of Freshwater Fish 24: 575-583.
Thorstad E, Uglem I, Finstad B, Kroglund F, Einarsdottir I, Kristensen T, Diserud O, Arechavala-Lopez P, Mayer I, Moore A, Nilsen R, Björnsson B, Økland F. (2013). Reduced marine survival of hatchery Atlantic salmon post-smolts exposed to aluminium and moderate acidification in freshwater. Estuarine, Coastal and Shelf Science 124: 34-43.
Of course, we greatly appreciate your gift, whatever it is! We love the idea that you appreciate our project and want to make it happen. And we have special attentions for those who contribute to the success of the project!
Student donor 5 Pounds: We greatly appreciate your support to Marie’s thesis! You and Marie will be friends forever on Facebook :)
Limestone donor 40 pounds. That’s great! Your donation will allow one otolith aluminium analysis. You will receive regular emailed reports on the progress of the project. You will be invited to attend the final presentation of the results live on the web.
Aluminium donor 80 pounds. Thank you very much for lending us your support! Your donation will allow two otolith aluminium analyses. You will receive regular emailed reports on the progress of the project. You will be invited to attend the final presentation of the results live on the web.
Silver donor 400 pounds: Fantastic! Your donation will allow the complete elemental mapping of an otolith. You will receive regular emails reporting on the progress of the project and a framed elemental map of your otolith. You will be invited to visit the lab and attend the final presentation of the results in Louvain-la-Neuve.
Platinum donor 1000 pounds: You will receive regular emails reporting on the progress of the project. You will be offered a framed picture of the elemental map of one otolith. You will be invited to join live broadcasts the presentation of intermediary results and to visit the lab attend the final presentation of the results in Louvain-la-Neuve. You will be invited to the Doctorate Honoris Causa Ceremony of the University of Louvain and to the Rector’s Concert.
Gold donor 3000 pounds: You will receive regular emailed reports on the progress and a framed picture of the elemental map of one otolith. You will be invited to join live broadcasts of a presentation of intermediary results as well as the final presentation of the results, live in Louvain-la-Neuve. You will be invited to an exclusive visit of the lab and a convivial dinner with the researchers involved in the project. You will be invited to the Doctorate Honoris Causa Ceremony of the University of Louvain and to the Rector’s Concert. Your contribution will be acknowledged on all publications emerging from this work.
For Belgian taxpayers, donations of 40 euros and above will be eligible for tax deduction.