Researchers at the SLU have suggest that herring stock in the Baltic Proper are being fished too hard

Researchers at the SLU have suggest that herring stock in the Baltic Proper are being fished too hard

Researchers at the Swedish University of Agricultural Sciences, SLU, have suggest that “restrictions on trawling close to the coast could be a good measure”, to protect local spawning herring stocks in the Baltic Sea. 

They also warn that “If we want fish stocks to have a healthy size structure, both management and research need to focus on developing and changing the management objectives that govern decisions at EU level”.

The comments follow the International Council for the Exploration of the Sea, ICES, annual scientific advice for 2022 EU fishing limits for the Baltic Sea that was released today. SLU also points out that herring in Baltic proper is being overexploited today. 

“The herring stock in the Baltic Proper is fished too hard today and spawning biomass is close to a critical limit for when juvenile fish production can be adversely affected. In addition, there are some uncertainties, mainly regarding the estimation of juvenile fish production in the near future, and we also know that there have been incorrect reports regarding the landings of herring and sprat. This leads to uncertainties in our results and can affect the catch thread from year to year”, says Mikaela Bergenius Nord, researcher at the Department of Aquatic Resources (SLU Aqua) and chair of the ICES working group WGBFAS, which works with advise for the Baltic Sea, to SLUs newswebb.

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In the Gulf of Bothnia, a review of the stock analysis has been made and here ICES raises the catch quota for herring by 81% already for the year 2021.

Since 2019, there have been uncertainties in the underlying data for herring in the Gulf of Bothnia, which has made assessment of the stock difficult. To address the problems, ICES has during 2020-2021 done extensive work to ensure the quality of data and calculation methods, which has resulted in a new stock model. Both the new model and its application in the new Council have been quality assured by international independent experts, according to SLU.

The analysis according to the new model shows that the stocks are larger than ICES previously calculated and that the stock has been fished at a level below the level leading to the management target MSY. For this year, 2021, ICES now instead recommends a catch of 117,485 tonnes, which is an increase of 81 percent compared to last year’s advice. For 2022, a reduction of 5 percent (to 111,345 tonnes) is then recommended compared with the new advise for 2021.

“The advise on fishing opportunities will increase so much for 2021 because with the new model we can now again give an advise based on Fmsy and not as before according to the precautionary principle. The new stock analysis also gives us a more secure picture of the amount of biomass over time”, says Mikaela Bergenius Nord.

Coastal fishermen witness sharply reduced catches

According to ICES assessments, there is therefore plenty of herring in the Gulf of Bothnia. At the same time, coastal and recreational fishermen are witnessing sharply reduced catches along the coast, according to SLU.

“The fact that coastal and recreational fishing can simultaneously experience a sharp decrease in catches is not because there is a shortage of herring in the Gulf of Bothnia, but because the presence of larger individuals has decreased, which is also seen in ICES analyzes. Coastal and recreational fishing is completely focused on large herring”, says Ulf Bergström, researcher at the Department of Aquatic Resources (SLU Aqua).

The reduction in large herring is probably due to several interacting factors. It is known that there are local spawning stocks of herring, although knowledge about them is incomplete. A high fishing pressure locally could thus lead to a reduction in certain spawning stocks, despite the fact that the stock as a whole is large. The growing population of gray seals, whose diet is mainly focused on large herring, can also contribute to the large herring being reduced locally.

Restrictions on fishing closer to the coast could be a good measure

In order to protect local spawning stocks of herring, discussions are being held on restrictions on fishing closer to the coast, by moving the trawl boundary or establishing conservation areas.

“Restrictions on fishing closer to the coast could be a good measure to increase the amount of large herring, but as knowledge of the herring migration pattern is limited, it is difficult to assess how effective such a measure can be. If you want to get back a higher proportion of large herring in the stock, a safer measure is to reduce the general fishing mortality, i.e. lower the catch quotas. But it is more difficult to implement and requires consensus with other affected countries because such a decision must be made at EU level”, says Ulf Bergström.

A contributing reason for the reduction of large herring is, according to the researchers at SLU, the goal of the EU’s common fisheries policy and management: MSY, Maximum Sustainable Yield.

“Fishing usually leads to the size structure of a fish stock shifting towards smaller sizes, as fishing is often directed at the larger and older individuals. Management according to MSY aims to maximize the long-term extraction of biomass from individual stocks without risking its reproductive capacity. Even though today’s management is sustainable according to MSY, there is no guarantee that large individuals will continue to be common in the stocks”, says Daniel Valentinsson, researcher at the Department of Aquatic Resources (SLU Aqua).

Objectives for a healthy size structure not operational

There are EU-decided management objectives for a healthy size structure for the commercial fish stocks, but that goal is not operational in the same way as the MSY goal in today’s management.

“Since the focus is entirely on MSY and a long-term maximization of catch biomass, today’s advice and management does not take into account the reduced occurrence of large herring. If we want to see increased consideration for the stocks to have a healthy size structure, both management and research need to focus on developing and changing the management objectives that govern decisions at EU level”, says Daniel Valentinsson.

ICES scientific advice will now be taken into account by the European Commission, which is developing quotas. Following negotiations between EU member states, a decision will then be made on the 2022 quotas in October.

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Article in Swedish: ”Sillbeståndet i Egentliga Östersjön fiskas för hårt”

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SLU: “The Herring stock in the Baltic Proper is being fished too hard”

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