A slippery tale of human greed, climate change and the mysteries of the deep
O n a warm morning in mid-March, a group of researchers from Ferrara University examine their catch after delicately emptying out a net from the mouth of the Valli di Comacchio, a vast system of wetlands in the province of Ferrara, on the eastern Adriatic coast of Italy. It takes a trained eye to spot a glass eel amongst the thousands of other tiny fish. Just over a year old, the eels are a few centimetres long, thin and spindly, and virtually transparent. The investigators count twenty-nine. One pauses and turns to his colleagues with something close to jubilation. “A success,” he declares, “usually, there are far fewer”.
Until a couple of decades ago, the same net placed around the same period of the year would have harvested at least a thousand glass eels, all destined to populate the surrounding wetlands, or ‘valleys’ in the local parlance. Much has changed since then. The number of eels arriving in Comacchio today is only two to three per cent of the figure for the 1970s and 1980s. Lifeel, the research project in which the University of Ferrara is participating, aims to understand the reasons behind the eel population’s steep decline, not just in Comacchio, but around the world.
LIFEEL is the first conservation project for the species conceived at the entire Po River basin scale, with the goal to increase and maintain the wild population of Anguilla anguilla (European eels).
It is a consequential project, because the ramifications of this drop are not just environmental. They are also economic and social, especially in areas such as Emilia and Romagna, where eels have long been the lifeline for many communities. It is ambitious, too: eels remain one of science’s great unsolved enigmas.They are such a mystery that it is difficult to know even what the risk of extinction is. No one can say how many of them there are in the world to begin with. And a reliable population estimate is the first criterion used by the International Union for the Conservation of Nature (IUCN) to determine whether a species is endangered or not. The second criterion is even trickier: in addition to an idea of the total population, you need to have an estimate of the number of “breeding individuals” – that is, the number of eels that are sexually mature, ready to reproduce. That’s where things get really complicated.
Eels do many things that no one has ever actually seen, not even by chance. One of the puzzles is how they procreate. The only thing scientists know for certain is that they reproduce in the depths of the Sargasso Sea, a region of the North Atlantic between the Azores and the Antilles. A sea within a sea. Scientists reached this conclusion because there, and only there, have they found the smallest specimens of eels at the first stage of their development, when they are called “leptocephali”: minuscule, flat and mostly translucent larvae, a few millimetres-long, with eyes barely developed. Eels from all over the world make the journey there to reproduce (only the species Anguilla japonica breeds elsewhere, near the Mariana Islands, in the Pacific). But why the Sargasso Sea? As yet, no one knows.
It took centuries just to weed out the most fantastic and bizarre theories about where eels come from. The Greek philosopher, Aristotle, claimed they originated from mud. The Roman historian, Pliny the Elder, believed they multiplied by rubbing against rocks, releasing particles of their body that would then turn into new eels. In the English countryside, people thought eels were born the instant the hair of a horse’s tail fell into water.
But their genesis isn’t the only mystery shrouding the species. Among the many other things, no human has ever been able to actually witness is, for example, the death of an eel just after it has reproduced – they are born and return to die too deep in the sea for us to know. Scientists are divided into two camps, engaged in a kind of philosophical dispute: some argue that finally observing an eel in the Sargasso Sea, dead or alive, would be in a sense pointless since we know eels are born and die there anyhow; others insist on the need for indisputable evidence.
What research conducted in recent decades has shed light on is what happens to eels in between their birth and death, in particular the two long journeys that define their lives: from the Sargasso Sea to Europe, and then back. The team of researchers from Ferrara University studies their arrival in Comacchio, the final stop on a journey of thousands of kilometres across the sea. At the historical Bellocchio fishing station, the researchers count the glass eels, measure and weigh them, and assess their health. Sometimes they take the specimens to a lab for further tests, before releasing them in the valleys.
Thousands of eels stay in the wetlands of Comacchio for years – nine, ten, sometimes more. After travelling half the world, they choose a spot and never leave it for almost their entire life. Others go up the rivers of the Padan Plain, the river Po, the Mincio. Before the dams and hydroelectric plants were built, they would make it all the way to Lake Garda.
From glass eels they develop into “yellow eels”.
"Yellow eels" European eels undergo five stages of development in their lifecycle: larva (leptocephalus), glass eel, elver, yellow eel, and silver eel.
Their bodies assume the features most familiar to those who fish and eat them: they turn into serpentine form, muscly, with a colour between yellow and grey, with scales so fine that are almost invisible to the naked eye. The mouth grows larger and the jaws become stronger. They feed on small fish, worms, larvae, frogs, snails, insects. They also love feasting on molting crabs, more vulnerable whilst they are shedding their carapace. If needs must, they don’t mind preying on small mice and chicks.“We have managed to trace the migratory route in the Adriatic Sea for the first 200 kilometres”
Mattia Lanzoni
At some point in their lives, if they are not caught, they decide that it’s time to reproduce and undergo another transformation. Their back turns black; the belly, silver. At this stage, they are called “silver eels”. Their fins get longer allowing them to swim faster, their eyes get larger and start turning blue which permits them to see better in the deepest parts of the sea. Reproductive organs develop, their digestive system stops working and they draw their energy from their fat reserves. They prepare for the long journey back to the Sargasso Sea, where they will reproduce and then die, exhausted.
To track this journey back is also quite a feat. Researchers place a device, a sort of tag, which allows them to identify the eels when they are subsequently caught by one of the fishing boats that work in the Adriatic Sea.
The second method consists of installing a subcutaneous transmitter, in the abdominal region. A series of buoys are then installed at a certain distance from one another in the sea, perpendicular to the coast, to draw a series of finishing posts, which work as sonars to trace the eels’ transit. “Of course, following them looks easy, but it isn’t”, says Mattia Lanzoni, a researcher in environmental science and protection at University of Ferrara. “We have managed to trace the migratory route in the Adriatic Sea for the first 200 kilometres”
In an era where everything is tracked and geo-localised this might sound trivial, but in reality, it is a huge milestone.
Talking with Lanzoni, a paradox at the centre of debates surrounding this species and its survival becomes clear. To understand why eels are disappearing one should be more interested in their health. The main drivers for such interest would come from fishing, gastronomy, and economic interests more broadly. Unfortunately, these are also amongst the main causes of eels’ sudden decline.
If we were to completely ban fishing, continues Lanzoni, we would lose the local presence of fishermen and with that the culture, the traditions, the social glue that sustains interest in the species: “It might sound bizarre, but we researchers collaborate with lots of fishermen: they provide us with constant updates as well as data to study eels. It’s in their interest.” It is not by chance that one of the places where eels are studied the most is Japan, where kabayaki – grilled eel – is a very popular dish.
A traditional Japanese preparation style where unagi (freshwater eel), is split, boned, skewered, and grilled while brushed with a sweet soy-based glaze.
Kabayaki A traditional Japanese preparation style where unagi (freshwater eel), is split, boned, skewered, and grilled while brushed with a sweet soy-based glaze.
Fishermen are also the first to pick up on the effects of climate change, which is another big factor explaining a drop in eels’ population. They don’t possess any scientific training or equipment, but they still notice that the environment is changing fast, that they don’t catch as much as they used to. All this information is useful to those doing research.
Luca Bellini is a vallante, a custodian of a vast wetland area close to the Po river delta. For years now he has been taking his small boat out onto the water just before dawn to see how the fish and birds are doing.
Each of the watercourses that make up the area surrounding Comacchio has its own complex system of sluice gates, depressions, canals. The water flows in from the sea and blends with the Po River’s freshwater, forming a wetland of brackish water with varying degrees of salt concentration.
At the entrance, there is a depression where the fish are divvied up: special grids, called lavorieri, block the transit of fish that are either too big or too small. After this first sorting, the fish move into a deeper depression where in winter they form themselves into a giant cluster, a ball, which allows them to protect themselves against the cold.
Lavorieri A V-shaped fishing net used in the Venetian lagoon to catch fish migrating to the sea.Just like bees, who also gather in this way, this sphere is called glomere. In the rest of the area the water is half a metre deep to facilitate oxygenation. All of this is the result of the work of the vallanti who partly follow and partly stir the natural course of the valleys.
Glomere is the word used to define the aggregation of bees when the temperature drops below 10°C. Through this spherical-shaped structure, bees can generate heat and thus avoid death by frostbite.Bellini explains that cold is the biggest threat to fish in the glomere, eels included. When it is too cold, the vallanti must close the sluice gates to prevent changes in temperature. The same when it is very windy. Each weather condition must be met with its own complex dance of countermoves, with the opening and closing of canals and ponds. Another thing to be borne in mind is the birds, especially cormorants, who cannot wait to plunge themselves into the glomere to feed. Every winter – Christmas and New Year’s included – no matter the temperature, Bellini stations his boat above the glomere to prevent cormorants from feasting on the fish. Unlike the vallicoltori – fish farmers who exploit the valleys intensively to turn a profit from fishing – the vallanti are closer to park rangers. “Our job is to maintain the biological balance between prey, predators, carnivores, herbivores, and the vegetation”, expounds Bellini.
Vallicoltori are traditional fish farmers who manage the valli, brackish lagoon enclosures in northern Italy’s Po Delta and the Venetian Lagoon. They practice vallicoltura, a centuries-old form of sustainable aquaculture, balancing production with ecosystem stewardship, working with natural tidal flows and fish migration patterns.
If cold presents a risk for the survival of fish, and thus for eels, one might be excused for thinking that global warming might be a magic bullet solution. Bellini explains that, in fact, things work just the opposite way: since it is now too warm, the uppermost stratum of water in the wetlands does not ice over as it used to, meaning that a layer which once protected the ponds from the coldness of the air is gone. “Fish and eels are much more exposed to the consequences of wind, which in winter can very quickly cause the glomere to grow cold, and make them die”, explains Bellini. “Without the ice the cormorants have an easier time hunting. We are also noticing ever more frequent, sudden changes in salinity which influence the growth of algae and oxygenation. It’s all changing very quickly.” Studies have shown how climate change can alter the direction and force of ocean currents. Even a small deviation in migratory routes the eels have to take means additional effort and distance. Not to mention the risk of missing the right current and ultimately the right moment to migrate, which may impact their chances of survival either on their journey to European shores, or on the way back, toward the Sargasso Sea.
The second reason for the decline in the eel population is the progressive loss of their habitat,
especially inland waterways – rivers, lagoons, lakes – made unreachable by the barriers built over the last century. Every dam, every hydroelectric plant, every drainage course or canal that diverts a waterway prevents eels from reaching the place where they would like to settle. In the last years, thanks to lobbying by researchers, funds have been allocated to build infrastructure that eels use to overcome the barriers they encounter, especially in the river Po and its tributaries, such as fish ladders or special canals called “fish passes”. It is, however, very protracted and costly work.
The third reason behind the steep decline in the eel population is that, despite bans and sanctions passed by the European Union, glass eels continue to be poached to be sold to fish farms outside the EU – in Asia – and for consumption. Many places along the European coastline have eel recipes that are kept as family secrets, passed down from generation to generation, considered a delicacy because they are forbidden.
Glass eels are caught with various tools, mostly circular nets called cerchie, which are positioned down the canals to block the eels from getting through. Depending on the stage of their development, every kilo of glass eels caught entails the death of thousands of other fish. Prices on the black market vary depending on the area and the period: in recent years, it has hit €9,000 per kilo.
The appetite for European glass eels by the Asian market is due to the decline of the local japonica eel population combined with continued high demand from Japanese consumers. The black market facilitates the contraband trade: since 2010, the European Union has prohibited the exports of glass eels outside its borders. In recent years, Europol, the EU’s law enforcement agency, has seized hundreds of kilos of glass eels destined for the Asian market.
All of this explains why today the number of eels that make it to Comacchio is only two or three per cent of the figure in the 1970s and 1980s, and why there is still so much to discover and unravel. Fishing data from the market of Chioggia are a good indicator of the drop: where up until the mid-1980s sales fluctuated around 80 tons despite significant dips and climbs, the last few years have seen them steadily decrease and then plummet, to an average of less than a ton.
The universities of Bologna and Ferrara are working on various studies to understand how to act, or at least, how to determine with greater precision the reasons behind the decline. Tracing the Mediterranean route is one of the elements of this work. But the most ambitious is to try to breed eels artificially. Oliviero Mordenti, professor at Bologna University, has been trying for years. So far, he has been able to hatch the eggs and make the leptocephali survive up to 40 days. It’s a historical result. No one has gotten that far before. But a key step is missing: how to feed the eels so they grow into adults.
His research is followed around the world.
