It is argued in several places that fishing removes nitrogen and phosphorus from the sea, thereby helping to combat eutrophication in the Baltic Sea. This is an argument often used by the fishing industry and can also be found, for example, on the website of the Finnish Natural Resources Institute. It was also one of the aspects highlighted when large-scale herring fishing in the Baltic Sea was MSC-certified in 2020 (the certification was revoked a year later due to the weakened status of the stock).
At BalticWaters, we have taken a closer look at this to see if the argument holds. A first examination conducted by Henrik Hamrén of the Baltic Sea Centre in 2021 indicates that nutrient removal through fishing is a marginal effort compared to the amounts of nutrients present in the Baltic Sea. According to his calculations, based on the quotas in force in 2021, Baltic Sea fishing for herring and sprat could at most remove about 6.4 percent of the phosphorus and 1.2 percent of the nitrogen annually added to the sea. Hamrén relied on Helcom’s 2017 figures on the amount of nutrients entering the Baltic Sea on an annual basis.”
If the same calculations are applied to Helcom’s updated figures from 2019, as we at BalticWaters have done, the total quotas for 2024 would imply a maximum extraction of 1440 tons of phosphorus and 8042 tons of nitrogen, corresponding to 5.4 percent and 0.9 percent, respectively, of the phosphorus and nitrogen annually supplied to the Baltic Sea.
Looking at Sweden’s quotas, this would mean that Swedish fishing would maximally extract 266 tons of phosphorus and 1485 tons of nitrogen, which is 1 percent and 0.2 percent, respectively, of the annual supply of phosphorus and nitrogen to the Baltic Sea.
The amount of nutrients in herring and sprat according to this research. 2,4 percentage nitrogen and 0,43 percentage phosphorous.
If you look at the total amount of nutrients estimated to be in the Baltic Sea, approximately 700,000 tons of phosphorus and 6 million tons of nitrogen, the total fishing by Baltic Sea countries extracts a marginal amount of phosphorus (0.2 percent) and nitrogen (0.1 percent)
The researchers BalticWaters has spoken to dismiss the argument of fishing as a eutrophication minimizer and claim it being meaningless and irrelevant.
– The thing is that if the entire food web is heavily disrupted by large-scale fishing, that has a greater environmental significance than a small, small change in the amount of eutrophication, says Bo Gustafsson, who researches eutrophication at Stockholm University’s Baltic Sea Centre.
What he means is that even if there is a small removal of nutrients through fishing, large-scale fishing has a significant environmental impact, and that it is a skewed comparison. He also points out that phosphorus and nitrogen in a natural cycle, such as in a fish body, are not problematic in themselves.
– The conversation easily focuses on the nutrients themselves. But it’s about the effects of too much nutrient input.
Human nutrient input to the Baltic Sea has decreased, as can be seen in Helcom’s latest report, but the input of nitrogen and phosphorus still exceeds the allowed maximum limit in several parts of the sea. When it comes to eutrophication, there has not been an improvement during 2016-2021 compared to the previous analysis period. Helcom mentions in its report that some of the nutrients are removed from the system “through activities such as fishing,” but at the same time they emphasize the significant proportion taken up by plants and algae, which can also store them in the seabed. Plant-based binding of nutrients is estimated to be worth 10.5 billion euros per year in saved costs for the countries around the Baltic Sea.
Even though the trend regarding emission reductions is positive, Bo Gustafsson points out that we will have to deal with old sins for a long time to come. Considering how humans have caused, and continue to cause, eutrophication in the Baltic Sea through continuous nutrient release, Gustafsson finds it strange to argue fishing as an environmental measure.
– It feels like greenwashing in order to maintain high fishing pressure.
He also emphasizes that we do not know enough about the importance of fish for nutrient cycling in the Baltic Sea and that one should not fixate on the amount of phosphorus and nitrogen in the body of the fish that is being taken out of the water.
– There may actually be positive effects on nitrogen and phosphorus sinks in the Baltic Sea from keeping the fish in the ocean.”
Conclusion
It is a minimal effort in combating eutrophication to extract biomass from the sea in the form of fish, and it may even be better for the marine nutrient cycle if the fish are left in place. It is also murky to defend an environmental measure with increased fishing pressure, which,
in turn, creates imbalance in the ecosystem.
Hope the water feels a bit less muddy now!
