This description is drawn from the Line Weighting Factsheet (May 2019) published by Birdlife International and ACAP for Pelagic Longline Fisheries.
- The mass of the weight attached to it
- The distance between the weight and the hook
A number of research projects have shown that adding weights to branch lines does not affect the catch rates of the fish that are being targeted and reduces the loss of bait to birds.
Problems and troubleshooting
Crew safety: ‘fly-backs’ (weights flying back towards the vessel after bite-offs or line breaks) are a concern when line weighting is used. Sliding leads that slide down the branch line during bite-offs greatly reduce the incidence of fly-backs. In the USA, fishers address fly-backs by altering the angle at which lines are retrieved so that crew members are not directly in the path of the weight should the line break. Personal safety equipment, such as helmets and face screens, and ensuring safe hauling practices, can help to minimise risks.
Propeller wash: to ensure that hooks sink quickly, they should be cast beyond the propeller wash, but still under the protection of bird-scaring lines.
Combination with other measures
Line weighting is considered to be one of the most important mitigation measures, but to maximise its effectiveness, it should be combined with bird-scaring lines and night setting. When used in combination, bird-scaring lines protect the area behind the vessel in which the baited hooks are still accessible to seabirds (up to 10-m depth), while the line weighting shrinks the extent of the area that the bird-scaring lines need to protect.
- ACAP. 2014. Report of Seabird Bycatch Working Group. Agreement on the Conservation of Albatrosses and Petrels, Eighth Meeting of the Advisory Committee. Punta del Este, Uruguay, 15-19 September 2014, AC8 Doc 12.
Birdlife International, ACAP (2019) Pelagic Line-weighting Factsheet. English, Bahasa Indonesian, Japanese, Portuguese, Simplified & Traditional Chinese.
- Gianuca, D., Peppes, F.V., Cesar, J.H., Sant’Ana, R., and Neves, T. 2013. Do leaded swivels close to hooks affect the catch rate of target species in pelagic longline? A preliminary study of southern Brazilian fleet. Agreement on the Conservation of Albatrosses and Petrels, Fifth Meeting of the Seabird Bycatch Working Group. La Rochelle, France, 1-3 May 2013, SBWG5 Doc 33.
- Jimenez, S., Domingo, A., Abreu, M., Forselledo, R. and Pons, M. 2013. Effect of reduced distance between the hook and weight in pelagic longline branchlines on seabird attack and bycatch rates and on the catch of target species. Agreement on the Conservation of Albatrosses and Petrels, Fifth Meeting of the Seabird Bycatch Working Group. La Rochelle, France, 1-3 May 2013, SBWG5 Doc 49.
- Melvin, E., Guy, T. and Sato, N. (2011) Preliminary report of 2010 weighted branch line trials in the Tuna Joint Venture Fishery in the South African EEZ. 4th Meeting of the Seabird Bycatch Working Group. Agreement on the Conservation of Albatrosses and Petrels, SBWG-4 Doc 07.
- Robertson, R., Candy, S., Wienecke, B. and Lawton, K. (2010) Experimental determinations of factors affecting the sink rates of baited hooks to minimise seabird mortality in pelagic longline fisheries. Aquatic Conservation: Marine and Freshwater Ecosystems. 20: 419-427.
- Robertson, G., Candy, S.G. and Hall, S. 2013. New branch line weighting regimes to reduce the risk of seabird mortality in pelagic longline fisheries without affecting fish catch. Aquatic Conservation: Marine and Freshwater Ecosystems. doi: 10.1002/aqc.2346
- Sullivan, B.J., Kibel, P., Robertson, G., Kibel, B., Goren, M., Candy, S.G. and Wienecke, B. 2012. Safe Leads for safe heads: safer line weights for pelagic longline fisheries. Fisheries Research (134-136): 125-132.