Double-weight branchlines are designed to reduce seabird bycatch in pelagic longline fisheries when used in combination with tori lines and in some cases night setting. The double-weight configuration is designed to 1) sink pelagic longline hooks beyond the range of seabird attacks within the aerial extent of a tori line during line setting, and 2) reduce injuries to crew should a hook come free while under tension in the landing process and recoil back at the vessel. Refer to ACAP's line weighting and bait sink rate factsheet for current weighting recommendations.
The double-weight configuration consists of two leads placed at either end of a 1 to 1.5 m section of wire or wire trace. This weighted section is inserted into a monofilament branchline 2 meters above the hook. The weight nearest the hook is free to slide along the branchline while the second lead is fixed. The double weight reduces the danger of weight recoil injury by: 1) spreading the mass of the weights (two smaller weights are better than one) across the wire trace, 2) including a sliding weight that dampens the speed at which the weight can recoil; including a 1 to 1.5 meter section of stretch resistant line (wire) which serves to also reduce recoil energy; and positioning the larger of the two weights in or near the hands of a crewman as the fish is under maximum tension as it approaches the sea door.
In 2010, over 95,000 branch lines with the double weight system were hauled with no injuries to fishermen, reducing seabird bycatch by 89% more than un-weighted branch lines, with no effect on fish catch rates.
Ease of Deployment and Safety
The double weight reduces the danger of weight recoil injury to crew members by spreading the mass of the weights across the wire trace, as two smaller weights are better than one, and by including a sliding weight that dampens the speed at which the weight recoils.
The double weight system is also easier to handle on deck than a single weighted swivel – it is easier to coil and it prevents jack-knifing as it is thrown into the water in line setting.
- Melvin, E., Guy, T. and Sato, N. 2011. Preliminary Report of 2010 Weighted Branchline Trials in the Tuna Joint Venture Fishery in the South African EEZ. WCPFC SC7-EB-WP-08.
- World Wildlife Fund (WWF). 2011. International Smart Gear Competition.
- World Wildlife Fund (WWF). 2011. Factsheet: Winner of the 2011 International Smart Gear Competition - Yamazaki Double-Weight Branchline.