Too warm, too many nutrients, hardly any fish – the Baltic Sea is not doing well. But little has changed in terms of the causes. What has to happen so that the Baltic Sea doesn’t soon become a dead sea?
Björn Fischer has just returned from his fishing trip on the Baltic Sea. He only caught flatfish. “They’re all thin. Apparently they don’t have enough to eat anymore,” he says. There are many reasons for the low fish stocks. For one thing, overfishing plays a role. With cod, however, it is greater than with herring.
The main problem with herring is that the water is too warm. The rise in temperature here is even higher than the global mean. Through the very small openings across the Belte and Sounde in the western part of the Baltic Sea, only a little fresh water gets into the sea. This is partly due to weak winter storms.
Herring hatch too early – and starve
On the fisheries research ship Clupea, the scientists from the Thünen Institute for Baltic Sea Fisheries are investigating how the current herring offspring are developing. During the spawning season, they are out and about in the Greifswalder Bodden every week to catch herring larvae. This research has been going on since the 1980s. The Greifswalder Bodden is the main spawning area for herring in the German Baltic Sea. The data you collect here is the most important basis for determining catch quotas.
At the same time, they are also an image of the Baltic Sea. Because when the Baltic Sea is doing badly, there are only a few herring, says Paul Kotterba. Due to the warmer water fewer herring larvae survive. Because the food, the so-called phytoplankton, which the herring larvae need to grow up, is only produced from a certain level of solar radiation. It needs a lot of light. But the herring will hatch when the water is warm. And because the water is now too warm even in the dark season, the herring hatches too early. But then there is not enough food, and millions of herring larvae starve to death.
Nutrients promote algae growth
But there are also too many nutrients in the Baltic Sea, according to fishery scientist Kotterba: “We can see that the plants on which the herring can lay their eggs are becoming fewer and fewer. That has something to do with how the water quality changes as a result of the nutrient input has.” Fertilizers, sewage treatment plants, car traffic and industrial wastewater carry nutrients into the sea via rivers. The abundance of nutrients causes algae to grow, making the water cloudy and depriving it of oxygen. And so the seaweed, the plant on which the fish lay their eggs, doesn’t get enough light. In the past 100 years, two thirds of all seagrass meadows in the Baltic Sea have disappeared.
The marine biologist Philipp Schubert from the GEOMAR Helmholtz Center for Ocean Research says it would be best if larger parts of the Baltic Sea were placed under protection. Because where both land and sea are under protection, you can already see a positive effect.
Baltic Sea National Park – the rescue?
This is exactly why the Environment Minister of Schleswig-Holstein, Tobias Goldschmidt, wants to protect large parts of the Baltic Sea. He would like to merge the existing protected areas in the Schleswig-Holstein Baltic Sea and thus found a national park. But there is resistance from many interest groups such as the tourism industry, but also from agriculture. You are worried about financial losses.
Just like Jens Alpers. He grows wheat and needs nitrogen fertilizer for his crops. He also knows that many farmers have used too much fertilizer in recent years: “There are certainly nutrient loads that could have been avoided.” Some of the fertilizer from the past decades is still stored in the seabed.
Today he has reduced his fertilizer use, says Alpers. Thanks to modern technology, there should not be too much fertilizer anywhere and a distance should be kept, especially near streams. But he’s not the only one working on the waters that flow into the Baltic Sea, he says. He sees operators of sewage treatment plants as having an obligation. For many years, the floodplain next to his fields has exceeded the target value for nitrogen. But basically the German rivers are far too heavily polluted.
No willingness to limit oneself for nature conservation
But not only those who are concerned about their profitability are against a Baltic Sea National Park. Even those who use the Baltic Sea in their free time don’t really want to be restricted. Many water sports enthusiasts believe that they can no longer practice their sport in the way they are used to. That’s why the Ministry of the Environment had organized a workshop with the water sports enthusiasts.
But he probably didn’t bring anything. The water sports enthusiasts don’t feel they have a duty – and the Minister for the Environment is frustrated: “I’ve heard a lot of suggestions for nature conservation here, but I’ve also heard that nobody says in any way: I’ll take a step back, do a little less. That wasn’t in the mood here at all.”
Marine biologist Philipp Schubert, who is also a passionate surfer and sailor himself, continues to fight for a Baltic Sea National Park: “Real protection simply means new rules and really adhering to the rules. That can also mean that there are no surfers at certain times Maybe there will also be bans on certain beaches. Yes, that’s the way it is. We have enough beaches.”