Fishering Service: Pulling the strings
The days of chasing fish and hoping for the best belong in the past, according to Andrey Fedorov, director of fishing gear manufacturer Fishering Service.
“Fishering Service has designed its Atlantica trawls to take advantage of the natural instincts of the fish, to be startled by loud noises and their instinctive urge for self-preservation,” he said, explaining that an understanding of the laws of physics makes it possible to steer fish right into a trawler’s gear
“The primary factor is that sound is the key information source for fish, and this is what dictates its behaviour. Even if a fish has not seen a threat, it senses it through vibrations in the water and seeks to retreat to a place where there is no noise. So this is where hydroacoustics become a tool that we can use. We created trawl gear in which each rope vibrates to generate an even noise field recognisable over some distance.”
The theory is that when faced with noise from every direction, fish will naturally seek out a place where the sound level is lowest, and this quiet place is the centre of the trawl.
“Each sound source creates its own unique acoustic signature, radiated in every direction. Environmental conditions and the sound source’s parameters define how this field is perceived by the fish. The towing depth and the configuration of the trawl in the water result in a unique acoustic effect. It’s not easy to engineer, and if there are spaces with little or no noise, then the fish can escape through these with only the small proportion of the fish that hadn’t been aware of the danger ending up in the codend,” he explained.
The rationale behind the design of the Atlantica trawls is to create an acoustic configuration that herds the fish together between the trawl’s wings instead of startling them into becoming dispersed, and for the shoal of fish to be shown a path to a safe place – which is the codend of the trawl.
Andrey Fedorov explained that achieving these effects depended on numerous independent studies and the painstaking research behind this took the company a decade and a half to achieve.
“Strong partnerships with Russian fishermen provided the opportunity to gather benchmark data, making it possible to test the theory based on these findings right away on board fishing vessels. This long process of research and testing has resulted in a substantial database of experimental information, making it possible to calculate behavioural patterns inside a trawl on a mathematical basis,” he said.
“By trying different trawl constructions, and by testing different materials and mesh shapes, the company’s fishing gear designers understood about the tensions that have to be applied to the specific bars in a trawl. Eventually we figured out that without exception each component should be tensioned as far as possible, so that in the water the bars play like the strings of a musical instrument.”
As part of this development, Fishering Service tested all the ropes available from numerous suppliers before taking the step of manufacturing its own ropes, providing it with control over the full manufacturing process and ensuring that even tensions can be maintained throughout the large-mesh section of a pelagic trawl. Balanced tensioning ensures that there are no under- or over-stretched bars, so the sound generated in the water is uniform.
Right mesh, right place
An important aspect of what Fishering Service’s designers have achieved is pinpointing the roles played by diamond and hexagonal meshes in the trawl mouth sections, and placing these where they are most effective in generating noise and quite zones inside the fishing gear.
Diamond mesh produces the highest sound volume as the gear is towed through the water, with the fish at the centre of a surrounding field of intense noise which guides them to the centre of the trawl’s catching zone.
According to Andrey Fedorov, the most popular pelagic trawls in use today use hexagonal meshes in the rope sections, which he feels provides no opportunity to equalise tensions on the bars.
“This applies particularly when a trawler is towing across the current, with the bars vibrating slowly and not generating enough noise to startle fish over long distances. In a small set of trawl gear, these meshes can still be effective in herding fish, but when a trawl has an opening of some hundred metres, then the noise generated isn’t enough.”
Conversely, the low noise generated by hexagonal meshes further down the trawl create a calm zone, the safe zone that the fish seeks out. This encourages them to move along without having a specific threat to avoid, before the mesh again changes to diamond mesh to push the fish back to the centre.
“This acoustic barrier forms the fish into a tight shoal at the centre of the trawl in front of the entrance to the machine-made netting section of the trawl. Getting this configuration and density right means that we can almost completely eliminate stickers in the meshes. While net designers around the world are looking at mesh sizes, at Fishering Service our designers have been concentrating on the shape and construction of the belly section, and experience has shown that the catching efficiency of our trawls made using this design approach is significantly higher than that of similar-sized conventional fishing gear.”
He commented that the company’s extensive research and the experience gained during this long process, plus its own software systems means that Fishering Service produces trawls not only for specific vessels, but also depending on specific species, water temperatures and water density.
“Our design software adjusts parameters for the fishing gear’s construction, depending on where the catching vessel is fishing, what the species and the conditions are, and other factors, such as fishing on the surface, midwater or close to the sea bed, as well as any specific requirements the customer may have,” he said.
“But there’s one principle all the way through all this – the tensions need to be right, so that a trawl can sing like an violin. The trawl also has to be able to absorb being deformed by the current conditions or by the trawl doors being mismatched, and if the trawl doesn’t make up for these factors, then the bar tension will be incorrect and fishing efficiency is lost.”
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