Pelagic trawling uses large nets made from strong, thin twine, which has the necessary strength and elasticity to handle the huge stresses involved in hauling large volumes of fish, especially in bad weather. Nets are generally shot and hauled from drums to reduce the risk of fouling the gear. The mesh size of the net decreases section by section, down to the cod-end.
Unlike demersal trawls very little or no bottom contact is required. If fishing near the bottom, the heavy weights on each lower bridle touch down first and keep the rest of the gear off-bottom. Ground ropes are not required, but chain can be added as ballast to the footrope to ensure the gear opens satisfactorily while shooting. The location of the shoals is determined by sonar or vertical sounder echoes picked up by the vessel.
|Potential Impacts (Biological/Environmental)||Gear Selectivity||Regulation|
• Capture of non target fish species (minimal as single species fishery)
• Incidental bycatch of cetaceans
• Capture/discarding of undersized target species
• Minimal - no interaction with seabed
• Mesh size
• Wing/net body design
• Height in water column
• Net size
• Minimum mesh size
• Minimum fish sizes
• % of catch mix retained on board
Improvement measures and initiatives taken by Scottish Fishermen
• Through 2005/6 Areas IV & VI had 400 pelagic trawl fishing operations monitored by the SMRU to record cetacean bycatch. None was observed on any of these trips.
• Scottish Industry/Science partnership is currently working to investigate technical measures which can be employed in Scottish pelagic trawls to reduce the capture of juvenile mackerel.
• Moves by industry to convert mackerel trawls to Dynema fibre (an extremely lightweight, strong, non-stretch, polyethylene) has reduced twine diameter, overall gear weight, and sweep and warp replacement. This has resulted in significant reductions to drag and savings on fuel consumption, thus reducing carbon footprint.
• Mackerel trawls are now incorporating hexagonal mesh sections of net in the wings and around the net mouth, which are reducing net drag and fuel usage.