Giant of the Danube is in danger of disappearing forever

The Huchen, which is only native to the Danube basin, only appears in remnants downstream, as the water researchers reported. The main reasons for the decline in stocks are the operation of hydroelectric plants that are not suitable for fish, river regulations that destroy habitats, increasing numbers of predators and rising water temperatures due to climate change.

The expansion of hydropower is particularly problematic. “About 80 percent of river stretches are currently in use, which is why hydropower in Austria can no longer make a significant contribution to the energy transition,” said Schmutz. Solar and wind energy, on the other hand, still have great expansion potential.

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Existing hydropower plants should be operated in a way that puts the least possible strain on fish stocks, he explained. This requires fish ladders, which even large fish such as the hucho can pass through. Compensation basins, in turn, can reduce flooding and low water levels caused by power plants turning on and off depending on people’s electricity needs. “Despite the corresponding EU laws, such measures are only very hesitantly implemented by power plant operators,” said Schmutz.

“River regulation is also seriously affecting the habitat of the Huchen,” the researchers reported. Although revitalization measures are being taken in Austria, this is not happening everywhere and very slowly. The hucho’s greatly weakened stocks would also be threatened by the protection of predators such as otters, mergansers and cormorants. Where hucho is still found, these piscivores “should be regulated accordingly,” Schmutz said.

“Climate change also poses a threat to the hucho population, as the average temperature of the Danube is now almost two degrees Celsius above previous values,” the researcher explains. In the upper and middle reaches, temperatures would remain, as expected, within a range where the hucho can survive the longest. Therefore, provide cooling there, for example by creating riparian strips for shade.

Huchen is in danger of extinction before it is fully explored
As the last link in the food pyramid, hucho would be a good indicator of the state of the water body. “When there are few fish in a river, there are few huchos, which indicates that the ecosystem is disturbed,” the release said. During the mating season, Danube salmon migrate upstream to find suitable spawning grounds, just like salmon. Whether they swim back to their place of birth has not yet been studied in detail. The huchen may therefore become extinct before its ecology can be fully investigated, said study co-author Schmutz of the Boku’s Institute of Hydrobiology and Water Management: “It is striking to me that, for example, the Amazon rainforest is regularly mentioned in the media with the A-call seems to be protecting biodiversity there, while species are going extinct on our doorstep.”

Two years ago, Schmutz and the former director of the Boku Institute, Mathias Jungwirth, decided to put together the scattered information from previous studies and databases. “We wondered what else we could do for such an endangered fish species,” says Schmutz. The analysis became a 170-page study involving, it says, numerous scientific and technical institutions, as well as fishermen’s associations and regional level experts from Bavaria and across Austria.

There was criticism of the lack of funding and a central point of contact for endangered species in Austria. The newly established biodiversity fund does not yet offer suitable options either. “So we had to individually convince everyone involved to participate in the study and hopefully in the rescue of the huchon,” Schmutz said.