Focus on the cormorant in a major project to save Europe's freshwater fish

The studies in ProtectFish consist of partly collecting and analyzing data for the EU-listed species of freshwater fish, their status, monitoring programs and the protection measures taken in relation to predators such as cormorants, and partly mapping the cormorant populations in the various EU countries. The project will include large-scale trials to regulate cormorants in selected watercourse areas, including on selected stretches of streams in Denmark, Austria and Poland.

But the black bird, cormorant, which can be observed sitting and drying its wings on gangway posts and other good places in the sun and wind, is an old natural part of the Danish fauna and food chains. So why do scientists think that cormorants eating freshwater fish started to become a problem?

"The cormorant is a bird adapted to life on the coast, where it hunts in both shallow and deep water. Despite a population of cormorants that increased more than tenfold from 1980 to 2000, there were no problems with freshwater fish in Denmark until 2010. But in the winter of 2009/'10, the cormorants in Denmark suddenly started hunting in streams and all the way up small streams, and the fish stocks couldn't cope at all," says Senior researcher Niels Jepsen from DTU Aqua, who is project manager for ProtectFish. He mentions a particular fish:

"Since then, despite many habitat improvements, improved passage conditions, i.e. removal of many of the barriers that have prevented the fish from finding the right spawning and breeding conditions - and good water quality, we have seen a significant decline for virtually all river fish, but especially the grayling is now threatened".

In ProtectFish, the researchers take the grayling as their point of departure as grayling is an indicator species, which will tell something about the ecological status of the watercourses.

The year 2010

When talking about the cormorant becoming a problem for freshwater fish in Denmark, Niels Jepsen specifically points to the year 2010:

"2010 was a very cold winter. The birds may have lacked food along the coasts and therefore started searching up in the streams. Then it turned out that it wasn't supposed to be a one-off performance. Since that year, the cormorants have been hunting freshwater fish – at the same time that the populations of our freshwater fish were only recovering after we have succeeded in restoring the habitats in the streams in recent years.”

Cormorants eat almost all fish from 5-60 cm in size. Therefore, large flocks of cormorants on the hunt are a threat to both fish that are about to spawn and the smolt itself, the young fish. A study in Kongeåen showed that even quite a few cormorants in a short time could cause great damage to the fish population.

Natural balance does not exist

In ProtectFish, places have been selected along rivers and streams around Europe, where regulation and scaring away will significantly reduce the number of cormorants, so that it can be investigated whether and, if so, to what extent regulation is the way forward to save the threatened freshwater fish.

In Denmark, regulation will take place in connection with the research project along stretches of Storå, Råsted Lilleå, Grindsted Å, Fjederholt Å, Gudenå and Vidåen.

Arguments in the outside world for not regulating cormorants are that nature must take its natural course. Prey and predator must find the balance themselves. But here the researchers object that nature is not in a natural, ecological balance in 2024:

"It has consequences when some species are protected. A species can be in low or high status, i.e. be threatened or become a problem. This is what my colleagues and I have documented has happened to the cormorant, which has increased significantly in number from a few thousand pairs just 40 years ago to now over 1 million. birds in the European population," says Niels Jepsen.

The cormorant was protected in all EU countries in 1980. Since then, the few hundred pairs that remained in Denmark took off and today are estimated to be around 30,000 pairs spread over 80-90 colonies. An adult cormorant eats 300-600 grams of fish per day.

"But it is important to understand that we are not after the cormorant as such - we must try to correct the completely skewed balance in our ecosystems, which occurs when a species is allowed to increase so violently in number that it threatens other valuable species, such as our fish in the rivers," says Niels Jepsen.

The DTU Aqua researcher points out that, in the end, there won't be any more food for birds and other animals that forage in the streams if we just leave the growing number of cormorants alone.

Favorable conservation status

In the motivation for the project, attention is drawn to the fact that the cormorant is no longer threatened while freshwater fish such as houting, grayling and salmon are on the EU's habitat directive's list as endangered species that require protection.

In relation to understanding endangered species, part of the task in ProtectFish is to discuss the concept of "favorable conservation status" - when has a protected species achieved a favorable status, so that it is no longer endangered and can reproduce itself?

As far as the cormorant is concerned, the favorable conservation status has long been achieved, Niels Jepsen believes:

"Already in 1997, the cormorant population in the EU was so large that it was no longer considered to require protection."

Finally, Niels Jepsen has a point about freshwater fish, which is about their status in our nature:

"Fish are also part of the important biodiversity - they are not just food. There has long been a tendency to talk about animals and birds as valuable species, important biodiversity, while fish are just referred to as something we eat. But fish are just as valuable species in ecosystems, just as important biodiversity in our nature," says Niels Jepsen.

Niels Jepsen is looking forward to working with ProtectFish across the EU to improve the conservation status of the threatened European species of freshwater fish, including our own pressured populations of grayling, trout and salmon etc., although he is well aware that the attitudes around to conservation status and management for birds and fish are very different and will require a lot of discussion.

ProtectFish just started in June. The consortium consists of universities, science institutions and stakeholders from the eight EU countries involved. Over the next four years, the parties must work towards the goal of coming up with potential political solutions for how to manage the life around our watercourses in the future, so that the species thrive together.

On the large scale, ProtectFish will contribute to meeting the EU's biodiversity strategy goals and the goals for good ecological status for streams and rivers, set by the EU Water Framework Directive (WFD) in the year 2000.