by Eva Baier
Hydroelectric power stations have a great influence on flowing waters.
They redirect natural streams, create basins with lake-like ecological conditions and prevent fish from freely moving up- or downstream. A risk-free downstream passage for fish is one of the biggest unsolved problems throughout Europe. It’s time to act: Join our campaign “Wanderfische” (migratory fish)!
A friend of mine called in February, “Have you heard? Dead and injured eels along the banks of River Rhine again!”, he said. I had heard. The timing is no coincidence, the eels commence their long journey towards their spawning grounds in the Caribbean in winter. No human has ever witnessed the mating or spawning of eels. From the discovery of a variety of large eel-larvae in the Western Atlantic we can however deduce that their breeding grounds must lie in the Sargasso Sea. A Danish biologist realized this about a hundred years ago, a theory which to this day has neither been proven to be accurate nor has it been refuted.
We know that the larvae reach European shores with a little help of the Gulf Stream and proceed to migrate upstream. After a couple of years -with advancing sexual maturity- the eels return to the Carribean. Or at least they try. The many hydroelectric power plants are blocking their way.
Fotocredits: Keystone / Gaetan Bally
There are so-called eel-ladders which have been built to allow the animals to migrate upstream. Additionally elvers are caught at the coast and transported to the upper reaches. The problem is the way back. The eels are especially troubled because of their length, the turbines split them in half or shatter their spine which leaves many animals gravely injured and unable to move or eat.
Power stations as deadly traps – I couldn’t get rid of this thought. I kept thinking about the dead eels along Rhine shores, so I drove down there the following day to see for myself. In one sidearm I found more a hundred dead eels. Let that sink in.
The eel is an endangered species which grants him a special protection status but unfortunately this doesn’t seem to make a big difference: In the core conflict between producing energy from hydro power and the unimpeded migration of fish, he’s on the loosing side. And he’s certainly not alone, he’s just one sad example of what happens underneath the water surface every day. All kinds of fish travel certain distances in rivers. All of them are in trouble if their habitat is sliced up. The downstream migration -as opposed to upstream- has been neglected for too long.
Today the consequences of producing hydro power are documented scientifically. Its effects on fish are dependant on the species, the animal’s size and technical circumstances, type and rotation speed of the turbine for instance. The longer the fish and the faster the turbines the more disastrous the migration. Apart from mechanical injuries caused by a contact with the turbines, the difference in pressure created by them can also have an indiscernible but fatal impact on the fish. In addition to this the power plants constitute a paradise for predators as below a station they will often find injured or disoriented prey.
The struggles of eels in the Rhine reveal further problems. Numerous power stations are built within short distances which creates a so-called “cumulative effect”. There are for instance no less than 21 stations between Lake Contance and the North Sea. From a purely mathematical point of view there should be a mortality rate of 20% per station, so that out of a hundred eels one will eventually reach the sea. In reality the mortality rate is more likely something around 70% per station, a horrible but much more realistic number, which if applied to every Rhine power station will out of a hundred see every single eel dead after only four stations.
Time to act!
The grave fate of migrating fish is meanwhile being discussed in political centres. Switzerland for instance has committed to ensuring a safe passage for migratory fish at all power stations and in both directions by 2030. The Water Framework Directive demands steps towards an unimpeded migration of fish within the EU.
What are applicable solutions if we want to keep using hydroelectric power stations? Generally speaking there are various approaches currently being researched all over the globe the most prominent of which is the “Leitrechen-Bypass” (rake bypass) which uses a rake to prevent the fish from swimming into the turbines. Instead they will be lead through a bypass. Other options and ideas are the employment of ‘fish-sparing’ turbines which would reduce injuries or implementing operational regulations for predictable downstream migration such as reducing the turbines’ speed or shutting them off completely, thereby allowing the animals to pass through the spillway gates.
Temporal regulation is a promising measure, at least for the eels as their migration occurs dependably periodical and over a relatively short period of time. In Germany these immediate measures are already being applied at a few power stations. Producers are reimbursed for the economic losses that occur. Many species do not however migrate synchronously or periodically, in their case these emergency measures are useless. Furthermore our knowledge of the mating, spawning and migration behaviour of many species is simply not sufficient enough to come up with satisfying solutions. The current options are limited in number as well as in feasibility. Solutions for large power stations with a flow rate of above 100 cubic metres per second are especially problematic, economically and ecologically. There is a lack of money, technical experience and -as noted above- knowledge about the migration behaviour.
And so the Rhine remains a death zone for eels. To improve conditions for domestic species’, the Swiss Fishing Association is cooperating with the fishing magazine “Petri-Heil” and environment protection agencies like WWF and Aquaviva. Together they’re trying to publicly stress the importance of fish protection and migration and starting the restructuring of large-scale plants. They specifically demand operational regulations and compliance with the current Water Protection Act which requires the provision of financial and personnel resources as well as investments towards research, specialist departments and the development of technical and operational solutions for large-scale plants. This calls for a vision/strategy on how to tackle the numerous challenges of the next ten years.
A petition helps to find a quick solution in Switzerland and everyone can easily participate, so that in a few years the eel may be able to migrate freely once more.
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Fotocredits Foto 1: Keystone / Gaetan Bally