One million dams threaten fish in Europe

One million dams threaten fish in Europe

Violet Field inPlanetJan 21, 2021 9 min read1 views

Discover, every day, an analysis of our partner The Conversation. Today, an ecology professor explains to us how human works are harmful to aquatic fauna

The Roselend dam in Beaufortin is just one of the 1.2 million river obstacles estimated in Europe - © DenDoktoor / Pixabay
  • In Europe, a fish can hardly travel more than 1000 meters without being stopped by large dams or low-head structures, according to a study published by our partner The Conversation.
  • Only a few very distant rivers are “spared”, like the Vjosa river which has its source in Greece and crosses Albania to the Adriatic without ever being impeded.
  • The analysis of this phenomenon was carried out by Karl M. Wantzen, holder of a UNESCO Chair in Rivers and Heritage, professor of ecology at the University of Tours.

The famous writer Franz Kafka has often described in his texts characters who try to achieve their goal without ever achieving it, hampered in their path by countless obstacles. This is pretty much what migrating fish and invertebrates that live in our European rivers must feel. Our study, published in the journal Nature on December 17, revealed that there is an average of 0.74 obstacles per km of river in Europe. This means that an organism can hardly travel more than 1000 meters without being stopped by large dams or by a myriad of low-head structures such as weirs, culverts, fords, locks, and ramps.

The movement of water is the essential nature of all water currents, from small streams to large rivers. But this natural movement, and in particular its variations which cause floods and droughts, was considered too dynamic for human beings, slowing them down in their desire to become "masters and owners of nature" from their earliest days, to use the expression of Descartes in his Discourse on Method. When kids play with sticks by the streams or when they create landscapes in their Minecraft video game, the dam is one of the first things they learn to build.

The Caban Coch Dam, in the Elan Valley in Wales © Sara Barreto / Nature (via The Conversation)

Controlling the power of floods, crossing rivers by bridges, controlling the flow for navigation, diverting the flow of water for irrigation ... all these techniques constitute the great art of engineering and an essential part of human culture.

Migratory fish all threatened

Until the industrial era, humans had only a local or regional influence on the environment and the consequences were relatively limited. Studies prove that the first construction of mills in the tributaries of the Rhine, which prevented the salmon from reaching their spawning grounds, reduced the salmon population by half… already in the Middle Ages. Salmon were so abundant at the time that despite this drastic drop, the populations remained large enough not to endanger the species. But until when?

Now, only a few very distant rivers flow unhindered, their waters flood and fertilize natural flood plains full of fish and flourishing vegetation, their sediments are carried downstream, building islands and even deltas in the sea. In Europe, One of those rare exceptions is the Vjosa River, which originates in Greece and crosses Albania to the Adriatic.

Adaptive management of barriers in European rivers (European AMBER project)

Most of the rivers of the "Global North", ie industrialized countries, but increasingly also developing countries of the Global South, have been fragmented into pieces. They hardly sink anymore, their sediments are blocked upstream of the dams, and their bed gradually erodes. The Ebro, Nile, and Mekong deltas are thus disappearing, receiving only a small percentage of the natural production of sediments from their upper reaches.

Fish in search of their spawning grounds are either blocked or weakened by a series of fish passes of which only a few survive. And even when they do, their offspring or adults migrating downstream are often cut into pieces while attempting to pass through a hydroelectric turbine.

As a result, almost every species of large migratory fish around the world has come to the brink of extinction, as if an invisible plan of eradication had been carried out for two centuries. For example, fascinating living fossils, such as sturgeon species that are 250 million years old, can hardly be seen except in zoos.

Other species that depend on migrants such as river mussels, which use them to transport their larvae, are threatened. This is the case of the Grande Mulette in Europe. Faced with these issues, awareness remains too slow, especially because traditional fishermen, keepers of fish, are themselves in decline all over the world.

International treaties have emerged, such as the European framework directive on water. They provide tools to tackle the subject, by removing certain dams, by diverting them or by releasing water according to natural flows. But the first step is to measure the magnitude of the problem: how many dams are there? Large dams, which are over 15m high, are visible on satellite images and in most countries require a registered building permit. It is therefore easy to identify them all over the world and to obtain precise information about them.

But smaller obstacles, low head dams, or even culverts, are often built without detailed formalities and are difficult to see from space. There is also a Babylonian confusion on the expressions used to name these constructions, even within a single country.

The main rivers in Europe, each basin being indicated by a different color. The thickness is proportional to the order of the watercourses © KM Wantzen based on data from Ecrins, EEA, Copenhagen

Identifying dams, a titanic job

Such challenges attract daring scientists like Carlos Garcia di Leaniz, a Basque-born fishery biologist and professor at the University of Swansea in Wales, Britain. As part of a Horizon 2020 project called Amber, he brought together researchers from across Europe to develop an atlas of these obstacles on the continent. A titanic job during which they faced many difficulties.

Field studies have made it possible to develop models of the number of obstacles not appearing on normal maps or satellite images or to develop predictors such as population density, in order to estimate the density of obstacles. obstacles in a given region.

A mobile phone application called a “ barrier tracker ” has been developed to invite citizens to contribute their observations to the verification of maps in the field.

The most complicated part has certainly been to collect totally dispersed and unverified information stored in thousands of pages of reports and in the deep memory of the computers of most institutions and administrations… and countries.

It was then that we met by chance. Both invited to an expert meeting in Chongqing, China, we found ourselves side by side on the tour bus in October 2016 at the Three Gorges Dam.

I had just successfully submitted a LeStudium (Loire Valley Institute for Advanced Studies) consortium project for several expert workshops, gathering information on the removal of the dam. Holder of a Unesco chair in Rivers and Heritage, I had the idea of helping to transfer the European and American experience in the removal of dams to the countries of the Global South whose societies are developing rapidly, an approach classic of the Unesco chair. So we decided to collaborate.

The Vjosa River stretches for more than 270 km from its sources in Greece, passing through Albania and then the Adriatic Sea. Although relatively wild, its lower course is threatened by several large-scale dam projects © Gregor Subic (via The Conversation)

France has long established a flow barrier (ROE) database, and this data could easily be transferred to the databases and models in the H2020 Amber project.

A laborious European collaboration

In other countries, the situation is more complicated. In Italy, there are dozens of expressions to qualify very similar types of obstacles. Due to the federal structure in my home country, Germany, each county (Bundesland) has a different way of recording data, although the Länder works together in a common working group, LAWA. With the help of the Federal Institute of Hydrology, we were finally able to have these data in a common format, with common terminology, so that they are now integrated into the Atlas of Barriers, which we can download free from the Amber website.

My experience has revealed to me the difficulties that persist in European collaboration around sustainable management of the environment. The institutional millefeuille, between countries and within countries, considerably hinders our work.

The results of the Atlas of Barriers, which were published in our article in Nature in December, are very shocking in two respects. On the one hand, the number of obstacles is much higher than what we expected, since it amounts to more than 1.2 million in Europe. In addition, nearly 10% of these barriers are obsolete and could be removed.


Our "Fish" file


How exactly do you remove them, and what to take into account when dismantling a dam ... researchers around the world (including us) are trying to answer these questions in the future, hoping that one day the sturgeon and other sensitive migrants will once again be able to freely follow the course of our rivers.

For this, society will have to go beyond its vision of rivers as a simple resource to be exploited, to leave room for a recognition of their role as the cradle of humanity, of essential life support systems, and of biological and cultural entities. to be preserved for their own nature. In short, that it develops “a river culture”.

This analysis was written in English by Karl M. Wantzen, holder of a UNESCO Chair in Rivers and Heritage, professor of ecology at the University of Tours.
The translated article was published on The Conversation website.