Pelagic Single trawling requires vessels with large horsepower as the nets can be more than half a mile long. The trawl is spread horizontally by cambered pelagic doors and vertically with heavy weights on each lower bridle. Pelagic doors also improve lift when towing speed is increased, and are used to raise the net when aiming for a shoal of fish. The net is continuously monitored using a net sounder, and net depth is changed by altering either warp length or towing speed.
|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.