Acronym Trålfangst
Category
Fisheries
Title Trålfangst: Årsaken til redusert effektivitet for enkelte tråltyper når fangsten øker - Trawling: The reason for reduced efficiency for some types of trawl when the catch increases Programme National Programme
Instrument (FP6)
Contact Type (FP7)
Strand (Interreg)
NA
Theme (FP7)
Activity Area (FP6)
Regional Area (Interreg)
Action (COST)
NA
Specific Programme (FP7)
NA
Funding source National Coordinator John Willy Valdemarsen Coordinator email NA
Coordinator institution
IMR - Institute of Marine Research (Norway)
Institutions involved
NA - SINTEF Ocean (Norway) ,
Start year 2010 End year 2010 Funding (€) € 195,145 Website https://www.fhf.no/prosjekter/prosjektbasen/900285/ Summary Fishermen experience that certain trawls / trawl types catch up to a certain amount of catch and that continued trawling through good fish registrations does not increase catch. The explanation given for this phenomenon is often that the catch in the trawl bag creates a "bucket effect" that prevents the fish from getting backwards and into the trawl bag. It is assumed that the fish go out through the large meshes further forward in the trawl. The other explanation for the fact that trawls catch worse in some situations is that increased load from catch accumulation significantly narrows the circumference backwards in the trawl bellows. This results in the accumulation of fish rather than the narrowing, and with increasing accumulation of fish, they will eventually be able to escape through the larger meshes further forward in the trawl. It is desirable to gain basic knowledge about what is the reason why some trawl types stop catching more fish when the trawl bag contains a certain quantity of fish. Through such knowledge, one will be able to implement structural changes to avoid such effects. This will also contribute to reduced fuel consumption. The tank experiments with the grid cone carried out within the project showed that the water flow inside a cylindrical net is not reduced in the opening, and that only reduced water flow was detected in the immediate vicinity of the net. The width of the area with reduced water flow increased backwards in the net cone, which is explained by frictional forces along the net and a boundary layer that is built up when the net is parallel to the tow direction. The experiments with a similar net cone towed at sea with M / S "Catch" up to 5 kn tow speed showed a similar flow pattern inside it. No reduced water flow was measured in the inlet, but a noticeable reduced water flow in the very vicinity of the network backwards in the network cone network than the actual water flow at distances more than 50 cm away from the network. The measurements of geometry behind the trawl bellows at different “catch loads” clearly showed that the cross section is reduced with increasing load from catch. The most important consequence of this is that the cross section is reduced for the various panels backwards (“Throat effect”). This means that fish come closer together when they are to fit through a net section, for example with a 200 mm mesh size. Closer to fish normally means that it panics and swims against the net wall.
Keywords
Gear technology;
Fishing technology;
Trawling;
Marine Region
13
Northern North Sea (27.IVa)
42
Barents Sea (27.I)
41
Norwegian Sea (27.IIa)
14
Skagerrak, Kattegat (27.IIIa)
4
Marine Region Map
