Inside Europe's Largest Flume Tank
What happens beneath the waves when a fishing net is at work? And how can a few small changes to its design make a big difference to the fish we catch and the seas we depend on?
These were just some of the questions our director, Jack Wing, explored during a recent visit to Hirtshals, on Denmark’s north coast. Invited by Seafish, the public body supporting the UK seafood industry, Jack had the opportunity to visit Flume Tank North Sea, Europe's largest flume tank and saw for himself how fishing gear is tested, studied, and improved.
At The Cornish Fishmonger, we believe great seafood starts long before it reaches the fish counter. It begins at sea, with the fishermen, their boats, and the fishing gear they use to harvest their fish.
So, when Seafish offered Jack the chance to see fishing nets in action and learn from the experts who design and test them, he jumped at the opportunity.
What exactly is a flume tank?
Imagine a giant tank of moving water where scientists and fishing experts can watch miniature fishing nets at work. That's essentially what a flume tank does.
By recreating the movement of water, it allows experts to test scale models of fishing gear, including trawl nets and the heavy underwater structures called trawl doors or otter boards. These doors help hold a trawl net open as it moves through the water.
Rather than having to guess what happens to a net beneath the waves, researchers can watch it in action, measure its performance, and see how even small adjustments affect the way it behaves.
The facility in Hirtshals is part of the North Sea Science Park, which brings together marine research organisations and technology specialists. It supports the testing and development of equipment used in fishing, aquaculture, and underwater technology, as well as training people in trawl gear technology. Fishers, net makers, scientists, and policymakers travel from around the world to learn from its expertise.
Why is this important? Much of what happens when a fishing net is in the water is hidden from view; in a flume tank, experts can see how a net opens, how water flows through it and how it interacts with the seabed.
They can then adjust the design or the way the gear is set up and see what changes. The aim is to make fishing more efficient, reduce unwanted catches and limit avoidable impacts on the marine environment.
What Jack discovered
Through demonstrations and conversations with the gear technologists, Jack gained a fascinating insight into how fishing equipment is evolving, and how innovative design can help fishermen work more efficiently while addressing some of the environmental challenges facing the industry.
Three things particularly caught his attention.
1. Giving young fish a chance to grow
Not every fish that enters a net needs to end up in the catch. Special features, such as escape panels and grids, can be built into fishing nets to give smaller fish and unwanted species a way out.
The details matter. The size of the mesh, the shape of the opening and where it sits in the net can all influence which fish escape and which are retained.
Seeing these designs tested in the tank helps experts understand how to make them work more effectively. The goal is to reduce the capture of undersized fish, giving more of them the chance to grow and reproduce before they are caught.
Over time, better selectivity can help support healthier fish populations, although the overall result also depends on how fishing is managed and how the gear is used.
2. Treading more lightly on the seabed
The seabed is home to a wide variety of marine life, from shellfish to animals and habitats that many fish depend on. The way fishing gear moves across it can make a difference.
The design and setup of nets and trawl doors influence how they interact with the seabed. Small adjustments can sometimes reduce contact or the amount of force applied.
Testing different arrangements helps experts understand how to balance effective fishing with efforts to minimise disturbance to seabed habitats.
It's a good example of how science, engineering and practical fishing knowledge can work together to improve the way equipment performs.
3. Making every litre of fuel go further
Fishing boats need fuel to move their gear through the water. The more resistance the gear creates, the harder the boat's engines must work.
By designing nets that move more smoothly through the water, experts can help reduce drag, the resistance that slows equipment down.
Less drag can mean lower fuel consumption, reduced running costs for skippers and crews, and fewer carbon emissions associated with catching the fish.
For fishermen, this can make a real difference to the economics of a trip. For the wider seafood industry, it's another way to work towards a lower environmental footprint.
Jack also came away with a greater appreciation of how all the different parts of a fishing net work together and why fishermen choose types of gear depending on the species they target and the markets they supply.
A particular highlight: the square-mesh cod-end
One of the most interesting parts of Jack's visit was learning more about the square-mesh cod-end a clever example of how a relatively simple design change can help smaller fish escape.
First, a quick explanation. The cod-end is the closed section at the back of a trawl net where the catch collects. As the net is pulled through the water, fish move towards this section.
In conventional diamond-shaped netting, the meshes can pull tight under tension, narrowing the openings and making it harder for smaller fish to escape.
Square-mesh netting behaves differently. Because of the way it's constructed and fitted, the openings can remain more open while the net is being towed. This creates opportunities for smaller fish to pass through the mesh rather than being retained with the rest of the catch.
Depending on the design and where the square-mesh panels are positioned, they can help undersized round fish, including young cod, haddock, and whiting escape, while retaining more of the larger fish the fishermen are targeting.
Of course, the results depend on factors such as mesh size, the fish species involved, and how the gear is configured. But the principle is straightforward: design the net so that the fish you want to release have a better chance of getting out.
For us as fishmongers, seeing this technology being tested was a valuable reminder that innovation doesn't always have to mean a completely new way of fishing. Sometimes, a relatively small change can make a meaningful difference.
More young fish escaping means more opportunities for them to grow and reproduce, helping support future stocks when combined with effective fisheries management.
Bringing the knowledge back to Cornwall
Jack also had the opportunity to see nets used by beam trawlers, a fishing method that has been part of Cornwall's fishing industry for around 80 years and remains familiar to our local fleet.
Understanding the equipment used by our fishermen gives us a better picture of what happens before the catch reaches us. It also helps us appreciate the experience, technical knowledge and practical decisions involved in bringing seafood to shore.
As Jack explains:
"I came away from Hirtshals genuinely impressed. Seeing the nets working in the tank and understanding how small changes in design can make such a difference to the fish, the seabed and the boats, was eye-opening. I'm keen to share the reality of how fish are caught with our team back home. It's another piece of knowledge and understanding about the industry we're proud to be part of, and it helps us all do a better job for our customers."
Jack Wing, Director
Why does all this matter to you?
When you buy fish, you may think first about its freshness, flavour and where it comes from. Increasingly, people also want to understand how it was caught and what that means for the future of our seas.
We share that interest. The type of fishing gear used, how it is operated and which species it catches can all influence the environmental impact of a fishing trip.
That's why we welcome research and innovation that help fishermen improve selectivity, reduce unnecessary seabed contact and use fuel more efficiently. These developments are important steps, even though responsible fishing also depends on good fisheries management and the wider conditions in which fishing takes place.
At The Cornish Fishmonger, we work closely with Cornish fishermen every day. Learning more about their equipment and the technology behind it helps us have better-informed conversations with them and with you.
It means we can better explain how different fish are caught, why fishing methods matter and how the industry is working to address its challenges.
Because we believe, knowing more about your seafood makes choosing it more meaningful. It's not just about enjoying delicious, fresh fish from Cornish waters; it's also about understanding the people, skills and decisions behind the catch, and the importance of looking after our seas for the future.
A little more about Seafish
Seafish is a public body that supports the UK seafood industry, from fishing and fish farming through to processing, retail, and restaurants.
Working with businesses, researchers, and government, it helps the industry develop skills, improve safety, respond to climate change and support more sustainable fisheries management. It also promotes the benefits of UK seafood at home and abroad.
Visits like Jack's help bring people together, share specialist knowledge and build a better understanding of the challenges and opportunities facing the seafood industry.
A huge thank you to Seafish for the invitation, and to the team at Flume Tank North Sea for welcoming Jack and sharing their expertise.
Curious about how your fish is caught?
We'd love to hear from you. If you have questions about fishing methods, the work of our local fishermen or where your seafood comes from, just get in touch with the team. We're always happy to talk fish!