Why are fish disappearing?

To begin with, some certainly worrying facts about the current state of affairs:

• The shortnose sturgeon is a species that used to be abundant in Polish rivers, but is now completely extinct.
• Salmon and huchin are still found in Polish rivers, but only thanks to human assistance.
  Twenty-four fish species are classified in the highest threat categories (out of 68 species found in Polish rivers).
• The majority of fish available in shops are farmed fish.

Looking out of the window, we can see for ourselves how much the environment around us is changing. We do not need any scientific degrees or studies to see how the greenery is disappearing and how the number of animals around us is decreasing. What we are not usually aware of, however, is that the situation in rivers and seas is also looking quite depressing. Fish have therefore been and are dying silently, unnoticed by the average person.

The last self-sustaining salmon was observed in the Vistula in the 1980s, and the last wild sturgeon was caught from the Vistula in 1965, weighing 135 kg. Even if we give up eating salmon for ethical or health reasons, we still associate it with an exclusive dish, which is underlined by its rather high price. It is therefore probably hard to believe that salmon used to be on the tables of even the least well-off and that this remained the case until the end of the 19th century. Already 100 years later, salmon consumption had become less popular, which clearly indicates a decline in the number of fish in Polish rivers. The reason is considered to be, among other things, the great hydro-engineering works. Nationalised in the 20th century, the fishery began to collapse, with the final crash occurring due to lack of fish.

What has caused fish such as salmon, sturgeon and eel to disappear from Polish rivers?

Of course, (as always) there are many factors, but the main ones include all sorts of obstacles on rivers, e.g. dams, weirs, thresholds, which have blocked the upstream migration of bi-environmental fish. Fish such as sturgeon, sea trout, chert and salmon spend part of their lives in the sea and breed in rivers. Eels, which also migrate, in turn reproduce in the waters of the Sargasso Sea, from there the eel larvae, carried by the Golfstrom, reach coastal European waters and eventually enter the rivers. The dams have also, of course, blocked the migration of fish species that move along the river but do not migrate to the seas.

Research confirms that the Wloclawek dam has caused a shocking drop in fish caught by fishing cooperatives. After its construction, catches turned out to be almost 30 times lower. The idea was to solve this problem with fish ladders, i.e. structures designed to allow fish to migrate upstream, sometimes downstream.Unfortunately, fish ladders are not only ineffective but expensive to maintain, requiring unblocking, cleaning and repairs.

In addition, they are designed with strong, well-migrating species and strong individuals in mind. Designing fish ladders for all fish species is not only expensive, but requires a great deal of knowledge of fish habits. Another weakness of fish ladders is that they do not restore sediment transport in rivers. The aforementioned Wloclawek fish ladder was upgraded in 2015, but the effect is still not satisfactory, as it is too small for sturgeon and only works one way.

The problem is making it difficult for fish to reproduce

Another factor of great importance for the life of the fish is the pollution of the waters and any work in the riverbed, e.g. dredging or gravel extraction. For example, a female salmon digs a nest with her tail fin in order to lay eggs, i.e. eggs. To do this, she selects a gravelly bottom, in places with clear cool water and a fast current. When the nest is ready, she lays her eggs in it, which, after fertilisation, are covered with gravel and this continues until the female has laid all her eggs. Eventually the gravel nest is about a 30 cm mound. Salmon also have an extremely developed ‘olfactory memory’, and it could be said that in order to reproduce, they return to their ‘hometowns’ because they remember the taste and smell of the water in which they spent their first years (the so-called homing phenomenon). Any work in the riverbeds during the spawning season is obviously destructive to this species.

Of course, more than one rescue mission was launched. The first and obvious idea to rebuild the salmon population was stocking.

The first stocking was carried out in 1879 and 1880, releasing salmon and sea trout hatchlings, and it was not until 1996 that a programme for the restoration of migratory fish was developed. Naturally, the natural development cycle of migratory fish was also taken into account, and the stocking plan included rivers such as the Rega, Parsęta, Łeba, Łupawa, Słupia, Gwda, Drawa, Radunia, Reda, Wda, Brda, Drwęca, Wisła, Bystra, Tanew, San, Wisłoka and Bystrzyca. Along with the stocking process, assessments of the effectiveness of this treatment were also introduced. Apart from the methodology, which has been improved over time, according to a WWF (World Wide Fund for Nature) report

salmon stocking in Polish rivers is, to put it subtly, not very optimistic and ineffective. The estimated survival rate of salmon (at the parr stage, i.e. the developmental stage of a yearling salmon fry) over three years is 1.48% on average. In practice this means that, for example, only 39 salmon were caught in the Krzyworzeka stream in 2005, which is not a satisfactory result as 20,000 were released.

What can we do? Nothing? And that may just be the best solution….

In light of the above issues, a growing number of global reports suggest that the solution with better results seems to be restoring naturalness in aquatic environments, rather than stubbornly maintaining the current state. The new approach also involves, among other things, a change in approach to water retention and management.