Line weighting means adding a weight near the hook to sink hooks quickly, so that seabirds eat fewer baits and less seabirds are caught.
Effectiveness
Line weighting can reduce seabird captures by 40% to 80% but scientific proof of this level of effectiveness is low.
Limitations
It takes around 20 to 25 seconds for weighted hooks to reach eight metres, so, without adding other mitigation measures, seabirds can still take baits and get caught. Adding a bird-scaring line and setting at night minimises the risk of catching seabirds.
Effect on fish catch
Overall, there is no evidence that the presence of weights near the hook affects target catch.
Minimum standards to be effective
There are three options to choose from:
- 40 grams or more attached a half metre or less from the hook
- 60 grams or more attached one metre or less from the hook
- 80 grams or more attached two metres or less from the hook
Another option is a sliding weight that is threaded onto the branchline. The sliding weight is designed to be safer for crew if the branchline flies back towards the boat. When a fish pulls the monofilament tight and bites the hook off, the sliding weight slips off the branchline.
Costs
Costs of line weighting include:
- lead swivels cost about US$0.25
- the hook with a swivel attached to the eye is US$1.30 – crimps are not needed with this hook type, so this is a cost saving
- sliding weights cost between US$0.60 to 0.80 each – when the sliding weight is made of a luminous material, light sticks are not needed so this is a cost saving
Sourcing materials
Hooks with a swivel attached to the eye can be found from Cookes.
Sliding weights are available from:
- Lumo Lead Fishtek Marine and Fishing International Supplies Hardware.
- Genuine GloLead Ocean Blue 60-gram – Fishing International Supplies Hardware
Problem solving
Problem: There is a safety risk to crew from weights flying back towards the vessel. Human safety is most important and risk of injury from fishing gear needs to be properly addressed.
Solutions:
Sliding weights are designed so they slide off the monofilament branchline when it stretches under tension. The manufacturer states that flybacks may still occur, so crew should be vigilant and wear personal protective equipment (PPE).
Similarly, the double-weight system is designed to be safer for crew from flybacks.
On some vessels crew haul the branchlines around a bar or pole so the weighted hook flies away from them. Another way is to haul from behind a screen.
It is important to make sure the crew have enough time to take care and do their hauling duties in an unrushed manner so they can stay aware of their environment.
Problem: When branchlines are stored in bins, they are heavier with weighted branchlines, so moving bins is harder.
Solution: If bins need to be moved, make sure this is done with the crew safety in mind and there are no obstacles in the way.
Problem: Weights lost during fishing.
Solution: Carry extra weights and replace any that have been lost during gear maintenance.
Case study
In 2014 and 2015, seven Republic of Korea tuna longline vessels operating off South Africa and Western Australia took part in a trial of sliding leads. The fishing masters were satisfied that the sliding weights made it safer for crew and didn’t affect fishing.
The vessels have continued to use sliding weights since the trial. This project involved Sajo Industries, Dongwon Fisheries and Dongwon Industries, the Korean National Institute of Fishery Science, FitzPatrick Institute of African Ornithology and BirdLife South Africa.
More information
Next steps: Learn about how to verify seabird safe practices
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