Whitefish Demersal Trawling
A typical trawl consists of a bag-shaped net with warps that lead to the fishing boat. The mouth of the net is kept open by trawl doors, which act like pressure boards using the force of the water to cause spread.
The Scottish whitefish fleet fishes using demersal methods, which mean that the nets are in contact with the seabed to a greater or lesser degree depending on the type of gear used. As the majority of Scottish whitefish fisheries are mixed fisheries, juveniles and unwanted species may be caught.
To combat this and to improve its selectivity, the Scottish fleet is subject to, and has initiated, a number of fishing gear regulations to mitigate these problems. It should be noted that in Scotland, to promote conservation, our fishermen use gears which have a larger mesh size and a smaller twine thickness than required by the European regulations. Also, certain attachments or twine configurations which are still legally used by other EU fishing nations are banned here.
Since 2001 the mesh size used by the whitefish fleet has increased from 100mm to 120mm. This has benefited the fishery and the fleet. Firstly, it has delayed the age of capture of many fish species, which means that significantly more fish go on to spawn than would have been the case with continued use of the smaller mesh.
Secondly, many netted small fish are now allowed to escape, which has reduced the levels of discards and helps to improve the size and value of fish caught by the fleet. This is an example of effective gear regulation, demonstrating clear benefit to sustainability of the stocks and to the commercial efforts of the fleet.
Beam trawls are used by a small segment of the Scottish fleet to harvest whitefish, mainly flatfish such as plaice and monkfish and other species found hard down on the seabed. Each net is fished from an outrigger boom, one on each side of the vessel with a beam at the mouth of the trawl to hold the net open. Tickler chains or chain mats on the bottom of the trawl are used to disturb the fish, causing them to rise up and enter the net.