Large cod most susceptible to injuries in seine fishing

Seine nets and traditional nets are the fishing gear most commonly used in fishing along the coast. Seine nets are considered as relatively gentle if the catch is not too large, and it is the type of fishing gear that has proven to be best suited for fish stored alive.

However, there is great variation in the size of cod caught with seine nets, which places great demands on both equipment and handling. A large cod weighing eight kilograms may need to be handled differently than a fish weighing two kilograms, both in terms of the catch situation itself, how it should be hauled on board, handling until delivery, and how it is handled once it has arrived on shore.

Over time, fishing companies have experienced challenges regarding the quality of the largest cod. This was the reason why two fishing companies joined forces with Nofima to document the loss of quality and see if good solutions could be found.

‘The bigger, the better’ doesn’t always apply to cod

Nofima has conducted several investigations into the quality of seine net catches. The trials have taken place over two seasons, involving catches of different sizes and from different vessels, which have handled the fish in slightly different ways.

The results show a clear correlation.

“Large cod are generally of poorer quality than smaller cod, regardless of how the vessel is rigged,” scientist Torbjørn Tobiassen at Nofima says.

The larger the fish, the worse the injuries. The recurring problem is that the big fish come out of the sea with a punctured swim bladder. This is a result of being pulled up quickly from the depths where the water pressure is high. When the swim bladder punctures, internal bleeding occurs that often produces discoloured loins. Smaller fish seem to tolerate this better.

In addition, large cod also suffer injuries when they are sent through tubes and pumps that are not dimensioned for that size of fish. In the project, the scientists have shown that pumping when using unfavourable tube diameters can break the spines of the largest fish.

“A relatively high proportion of cod over eight kilograms had internal injuries, which were not necessarily visible on the outside. Such injuries pose major challenges for the fishing industry,” Tobiassen says.

Injured fish are bad economy

This problem is an important one to solve for the industry players participating in the project.

“We don’t want to deliver injured fish to our customers. It is a financial burden that large fish cannot be used for the products that generate the most money, and we get a lower yield from the raw material. If the quality can be improved, it would mean a lot for our production,” Terje Sørensen from the fish producer Brødrene Karlsen says.

When the cod is delivered, it is processed into various fish products. Much of the fish is sold round (gutted, with or without heads), and it is not necessarily that easy to find out whether the fish is injured.

Cod that cannot be used as planned due to bleeding and other injuries, for example, salted cod or clipfish, represents a significant cost for the fishing companies.

“It is disheartening to receive feedback that the fish we deliver have injuries that lead to downgrading. We want to solve these challenges and deliver fish of the highest possible quality. It has therefore been positive to participate in this project in order to get new input regarding improvements to the equipment on board, but also in terms of the catch process itself,” Rune Sand, captain of the seine fishing vessel called Fortuna, says.

Research continues

Both scientists and industry players have expectations from the next phase of the project.

“We have now documented the injuries in the fish. In future work, we will continue to test different methods to see if anything can be done to raise the quality of the larger fish,” Tobiassen says.

It is likely that most of the injuries occur when the fish are caught.

Trials involving towing speed and haul time (the time it takes to haul the net up from the bottom) are planned ahead of next season, and the scientists will also study the effect of codend releasers which give the fish more space in the net. The trials will be carried out in close collaboration with several vessels.

In the further work, the scientists will also map what happens to the quality when the fish are pumped on board through tubes from the net, and when the entire net is lifted on board. In addition, the quality during storage on board in the hold will be further investigated.

Reference:

Tobiassen et al. Quality challenges with large cod caught with Danish seine. Knowledge status from previous research, Nofima report series 24/2021, Nofima AS, 2021. Summary.

This article/press release is paid for and presented by Nofima The Norwegian Institute of Food, Fisheries and Aquaculture Research

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