Difficult times for trout, egli, eel or whitefish: The stocks of freshwater fish have decreased by 90 percent across Europe since the 1970s. This is shown by an investigation by the WWF. Switzerland is also not exempt. Andri Bryner from the ETH Zurich Water Research Institute (Eawag) knows more about the reasons for the dramatic slump.
SRF News: Are Swiss waters also affected by the massive decrease in the amount of freshwater fish?
Andri Bryner: Unfortunately, the trend can also be seen in Switzerland. Before 2000, we started a project with the cantons, the fisheries association and the chemical industry to investigate the reasons for the decline in fish.
For example, we noticed a 70 percent drop in trout between the 1970s and 2000. And if you look at the fishing statistics for the years 2000 to 2018, you can unfortunately see another 40 percent decline in the number of fish caught.
What do you know about the causes of this decline in fishing, in the case of over 80 percent since the 1970s?
There are three main reasons for this: the construction of the rivers, the material pollution of the water and diseases that are partly related to global warming.
The reasons are obstructions, water pollution and diseases related to climate change.
In addition, there are local factors, such as a strong increase in fish-eating birds in some places – such as cormorants or sawducks. Competition from invasive, i.e. exposed fish species, which compete too strongly with local fish, could also be responsible for the decline in some places.
What can you do about the decline in fish in Swiss waters?
First, the habitats for the fish must be upgraded. Above all, the continuity in the rivers has to be improved. The fish must be able to migrate from the rivers to the lakes and vice versa. In addition, structures must be created along the water in which the fish feel comfortable, find shelter and can reproduce. The key word here is: revitalization of the waters and the banks.
The fish must be comfortable and able to reproduce.
In addition, the water must be kept clean. Great efforts have been underway in this area for several years. Many sewage treatment plants are equipped with an additional purification stage, which can also remove pharmaceuticals or household chemicals from the water. However, pesticides from agriculture and from gardens continue to cause problems – we still have to make progress here. It is also important to manage the fish stocks carefully: in the past, many fish from fish farms were abandoned and it was not noticed that some diseases had been introduced into previously healthy waters.
So as a consumer, I can also do something: make sure that I put less chemicals into the wastewater?
One thing is certain: for fish, the less medication and chemicals get into the wastewater and thus into the rivers and lakes, the better. On the other hand, it is not a question of no longer eating edible fish from Swiss waters. These can be enjoyed without hesitation. But it is also clear that we cannot meet the increasing demand for fish from local waters.
The interview was conducted by Susanne Stockl.