Text: Henrik Hamrén
Increased trawl fishing on flatfish risks further damaging Baltic cod stocks
The Baltic Sea countries in BALTFISH want to introduce new selective gear for flatfish fisheries to decrease cod by-catches. Only one of the trawl models can spare the large and ecologically important large cod – but according to BALTFISH it should only be mandatory in the southwest Baltic. Elsewhere, new gear may make things even worse for the cod.
Trawl fishing for flatfish will probably increase in the Baltic Sea next year. At the same time, cod by-catches must be reduced since the cod stocks are in such poor condition.
Eastern Baltic cod stock fisheries have been closed since 2019. The same will happen for the western cod stock next year. Then, cod can only be caught as by-catch in other fisheries – up to a maximum of 595 tonnes for the eastern stock and 489 tonnes for the western stock.
Hence, fishermen must target other species. In the southern Baltic Sea, Denmark, Germany and Poland are engaged in quite extensive trawl fishing for flatfish. And next year the total allowable catch (TAC) for plaice will increase by 25%, to a total of 9,050 tonnes.
This carries risk, as it is difficult to trawl for flatfish without also getting cod.
Hardly any large cod left
One obvious risk for next year is that fishermen will get too much by-catch of cod, and start discarding cod illegally in order to be able to fill their flatfish quotas.
But perhaps the most serious threat to cod stocks is that increased bottom trawling will kill the few large-sized cod that remain, according to Henrik Svedäng, researcher at Stockholm University's Baltic Sea Centre.
– Since the 1990s, cod fisheries in the Baltic Sea have been increasingly focused on catching the largest individuals. This has contributed to the serious situation we are seeing today for, for example, the eastern stock, where there are hardly any large cod left, he says.
His study of changes in the size structure of Baltic cod stocks shows that the shortage of large-sized cod has never been as great as it is now. This can have a number of negative effects, not least because large female cod are extremely important for the reproductive capacity of stocks.
– A more balanced catch makes good use of the stock growth potential. It also reduces the risk of evolutionary changes that you don't want, such as premature sexual maturity, Henrik Svedäng says.
The presence of large predatory fish is also important for the functioning and structure of the marine ecosystem. A good age and size structure of fish populations is also one of the criteria for “good environmental status” under the EU’s Marine Strategy Framework Directive (MSFD).
– We should therefore try to preserve large predatory fish both for the productivity of the stocks and for the ecosystem as a whole, says Henrik Svedäng.
A new ‘toolbox’ for fisheries
So, will it be possible to increase catches of flatfish without getting more cod as by-catch?
The members of the regional body BALTFISH* believe that a solution has been found. Recently, they submitted a joint recommendation to the European Commission, to introduce different gear requirements. The trawls that are now allowed to be used are designed to fish for cod. The idea is to adjust these trawls so that they sort out the cod but retain the flatfish.
In the proposal, BALTFISH presents several different trawl variants. All were developed by a research group led by Daniel Stepputtis at the Thünen Institute in Rostock, Germany (also in some collaboration with Swedish and Danish researchers).
– We have presented a kind of ‘toolbox’ of different types of trawl modifications that, under different conditions, can help reduce cod by-catches, says Daniel Stepputtis.
Different versions of the Codend-based trawl, with various adjustments. Graphic: Thünen Institute / A.Schütz
Large cod get stuck in the trawl every time
The adjustments made in the so-called Codend models (see picture above) mainly work with special types of netting and attached lines to ensure that the meshes stay open despite the tow pull. It allows a larger fraction of the cod to escape.
Codend models can be effective and achieve decent results in reducing cod by-catches – as long as the cod stocks consist only of small cod of up to 35-40 centimeters. Larger cod can’t escape through the meshes, according to Daniel Stepputtis.
– One must also keep in mind that cod stocks change over time, so using Codend requires regular monitoring of the stock so that you always know what the size structure is where you fish, he says.
And either way, Codend always catches the big cod.
– The large cod over 50 centimetres get stuck in the trawl every time, says Daniel Stepputtis.
We know it works
Given the catastrophic situation of cod stocks in the Baltic Sea, there is also a need for a flatfish trawl that let the larger cod escape. Daniel Stepputtis and his team has managed to develop a model that does just that. They call it Roofless.
– Roofless is the only trawl variant that is not size dependent. The design allows cod to escape no matter how big they are, he says.
The centrepiece of Roofless lacks a "roof" (see picture). Cod swimming inside the trawl can therefore get out through the opening in the “roof” before being pressed together with the other fish in the trawl bag at the end of the trawl.
– We know it works, we have tested it several times and in different areas, says Daniel Stepputtis.
The Roofless model, combined with a Codend in the end of the trawl. Graphic: Thünen Institute / A.Schütz
The best choice for cod stocks
The Roofless is always used together with a Codend model in the end of the trawl. Tests with this combination in the southern and eastern Baltic show a sharp decrease in cod by-catches compared to tests using only Codend.
And above all, the Roofless-Codend combination (see picture) catches very few big cod.
– If you really want to achieve the best by-catch reduction for cod when trawling for flatfish, you must use Roofless combined with Codend, says Daniel Sepputtis.
The only downside is that Roofless is slightly more expensive than the other proposals and also has to be handled a bit differently on board compared to only using a Codend, which is basically a traditional bottom trawl.
– If the fishermen themselves get to choose, most of them will probably choose Codend, says Daniel Stepputtis.
Assessed by EU experts
The question is which of the new gear will be used next year. The European Commission has sent BALTFISH’s recommendation to its scientific expert committee, STECF, for an assessment.
– We will assess whether it is compatible with a number of different articles in the EU's technical regulations within the framework of the common fisheries policy. Then, of course, we will also assess the quality of the scientific data behind the proposals, as well as controllability, and more, says Daniel Valentinsson, researcher at the Swedish University of Agricultural Sciences (SLU Aqua) and one of the experts in STECF.
How important will the ability to select and spare larger cod be in your assessments of the various gear?
– As I see it, that aspect is part of the assessment of the proposal's broader stock and environmental effects, and also of how compatible the proposal is with environmental legislation. But I do not yet know how it will finally be assessed, says Daniel Valentinsson.
The researcher behind the proposals, Daniel Stepputtis, would only choose the Roofless combination because the Baltic cod is in such poor condition. What do you think about that?
– Personally, I completely agree with Daniel's evaluation there, says Daniel Valentinsson.
Large cod escaping from a Roofless trawl. Photo: Thünen Institute
The by-catch goal is arbitrary
The joint recommendation from BALTFISH is more of a compromise, which means that different gear can be used in different subdivisions (SD:s) of the Baltic. The overall goal is to achieve at least 55% weight loss of cod by-catch compared to the gear that is currently used.
– It should be mentioned that cod quotas have decreased by 98-99% since the time when these trawls were first introduced. So, a 55% reduction in cod by-catch is an arbitrary figure that comes from a political agreement, says Daniel Valentinsson.
Pretty cynical reasoning
In the BALTFISH proposal, the choice of new trawl models depends entirely on how much larger cod there is in each subdivision. Because even though large cod is a scarce commodity in the entire Baltic Sea at the moment, the situation is not exactly the same in all of the subdivisions.
BALTFISH argue that Roofless should only be mandatory in the southwest Baltic Sea (SD 22-23), where the proportion of large cod (too large to escape the Codend models) is greater than in cod populations further east.
In SD 24-26, where there is proportionally fewer large cod in the population – and where a 55% reduction of cod by-catch is therefore easier to achieve without Roofless – the fishermen should be free to also chose Codend models if they want to.
Trying to avoid a by-catch of larger cod in the western stock but not in the eastern stock, where the risk of catching large cod is less, is ‘a pretty cynical reasoning’, Henrik Svedäng thinks.
– Since the eastern cod stock has the lowest proportion of large cod, it is also where the large cod are most valuable to the stock, he says.
A huge and necessary step forward
New selective flatfish trawling gear can enable fishermen to catch more flatfish before the by-catch limit for cod is reached. So far, Roofless is the only size independent alternative.
With Codend, more small cod will escape compared to traditional trawl gear. Consequently, if there happens to be larger cod where the fishing takes place, and the fishing effort in fact increases, the Codend by-catch will have a higher proportion of larger cod compared to the by-catch with both Roofless and traditional trawls.
– Even if the current proposal is maybe not perfect, it is a huge and necessary step forward, and long overdue. We do hope that fishermen and scientists use the next year to discuss, develop and test better options to help the Baltic cod stocks to recover, for the sake of both cod and fishery, says Daniel Stepputtis.
* BALTFISH is a regional body where ministries and various stakeholders from the EU countries around the Baltic Sea meet and discuss fisheries management issues. BALTFISH can submit joint recommendations to the European Commission on various fisheries issues.