Fish death in Oder: a disaster for birds and mammals so far harmless

Only draft horses were affected
Or the tragedy is not dangerous for wild animals yet

After the fish died in the Oder, experts at first give all the clarity to the inhabitants of the animal lands: so far it seems that only species of cold-blooded animals were affected by the disaster. So far, birds and mammals have been saved. However, there are a number of obstacles to the river’s recovery.

Whether it is the kingfisher, the white-tailed eagle or the otter: there is a whole range of rare and protected species in the Oder region. According to experts, the massive killing of fish has so far not posed any danger to many. “According to current knowledge, only cold-blooded animal species, such as fish, mussels and snails, are affected,” said Dirk Trichel, president of the Lower Oder Valley National Park. The so-called cold-blooded animals include fish, amphibians, and reptiles, but not birds and mammals.

According to Treichel, in addition to the hundreds of tons of dead fish that have already been recovered along the Oder, there are now also huge carpets of dead water snails near the shore. Many dead sea mussels also float on the surface of the water. “We assume that otters now also ate carcasses or dying fish,” Trichel said. “But no dead specimens have been found.” “Ornithologists have discovered two dead birds and five dead ducks. However, it is not clear that there is a causal relationship to the fish deaths,” added Christian Walter of the Berlin Leibniz Institute for Freshwater Ecology and Inland Fisheries.

Table salt promotes algae growth

Last week, Walter and his colleagues reported the robust growth of the algae species Prymnesium parvum, which can form a toxin that can kill fish. “This poison was detected in large concentrations in the Oder, which would have been the cause of death,” Walter said. The mass development of algae was only possible due to the high concentration of salt in the river water. “My colleagues discovered it was table salt,” Walter says. “It’s well suited to growing algae.” It is assumed to be a waste product from industry. “But I don’t know which process produces such amounts of common salt and why you should throw it out when the water is low.”

There have already been various other cases of mass fish deaths caused by algal toxin around the world. “No similar disasters have been reported that also affect warm-blooded animals,” Walter said. But the Oder disaster could reduce the supply for species such as herons and cormorants that hunt live fish. “However, these species can also escape into surrounding waters without having to significantly change their area of ​​approach,” Walter says. Sea eagles also eat dead fish. “They have no problem with that.”

Oder was considered a very fishy body of water until he killed the huge fish. “About 50 species have been discovered in the Oder, including some special ones such as loach, sap, and mudflake,” Trichel said. Aquatic ecologist Walter hypothesizes that some fish survived. For them, however, the lack of oxygen, which will still occur when the algae decomposes, could be dangerous.

Shipping expansion as a risk factor

The chances of the river’s recovery are estimated to be good. “The Oder benefits from the fact that it has no barrier to the sea,” says Walter. “The fish can migrate in and out without our intervention. The fish will avoid the devastating wave and can migrate again afterwards.” “The fish have a high reproductive capacity,” says the aquatic ecologist. “I think in two to three years, we will only be able to get a sense of fish mortality from the age pyramid.” Then there will be mainly small and relatively small fish – which, however, will be a problem for fisheries.

A great danger to Oder from his point of view: the planned expansion of shipping. “This doesn’t quite align with river recovery,” Walter says. “With the Oder disaster, we’ve learned again that we have to try to prevent low waters and not let them show up in the first place.” Expansion is also not an economic concept and the small number of ships is disproportionate to the effort expended.

As the director general of the Senckenberg Nature Research Society, Clement Tockner, warned against the expansion: “This is disastrous for Oder.” The creation of a deeper corridor will lead to a lowering of the groundwater table in adjacent areas. More dams are also planned. All this leads to a massive deterioration in the environmental situation, according to Tokner. “You upgrade the river for one job at the expense of many valuable services. The river provides recreation, is a valuable ecosystem and retains water in the landscape – at low tide. All of this will suffer from the upgrade and this can lead to much greater damage.”

(This article was first published on Thursday, August 25, 2022.)

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