Night or day setting refers to the times of day when longliners** set, soak and haul their lines. These variables are inherently linked to the duration of the soak (the period that the longline is in the water). Timing depends principally on the target species, but also varies among fleets and regions. For example, around the Hawaiian archipelago, longlining for tuna occurs during the day at 150 to 400 m of depth, generally to the south of Hawaii, while longlining for swordfish occurs at night in areas north of Hawaii less than 100 m in depth . In contrast, Taiwanese, Chinese and Australian longliners have used shallow setting at night in some areas to target large bigeye tuna . Other variables may also come into play, such as weather and fishing success (boats will keep fishing if the catch is good). Some Regional Fisheries Management Organisations regulate the time of set, soak and haul (refer to the BMIS Regulations database).
What is it and how does it work?
Night-setting is particularly effective on moonless nights. The effectiveness of night-setting is reduced during bright moonlight and when using powerful deck lights. ACAP recommends that for night-setting to be effective, line setting should not commence until after nautical dusk and should be completed before nautical dawn, when the sun is still below the horizon. The exact times of nautical dusk and dawn are set out in the Nautical Almanac tables for the relevant latitude, local time and date. It is important that the entire set is completed at night. Many seabirds are active at dusk and dawn, and research has shown that sets that occur largely at night but continue into twilight and daylight hours are often associated with high levels of bycatch. Deck lighting should be kept at the minimum level appropriate for crew safety and directed inboard so the line is not illuminated as it leaves the vessel.
Problems and troubleshooting
Night-setting is only truly effective on dark nights. In the highest latitudes during the summer months, the time between nautical dusk and dawn is limited. The time of setting may have unfavourable consequences for the catch rates of target species, or other taxa caught as bycatch.
Combination with other measures
Due to variations in the moon-phase, and the ability of some seabird species^ to forage at night, night-setting should be combined with line-weighting and bird-scaring lines.
^E.g., White-chinned Petrels, Procellaria aequinoctialis
The time of setting may have unfavourable consequences for the catch rates of target species, or other taxa caught as bycatch.
Does not require gear modification. Costs may accrue if time of setting causes a reduction in target species catch.
- Assessing the effectiveness of bird scaring lines and branch line weighting at night needs to be determined, possibly by way of using thermal or night vision technologies.
- There is concern that night-setting may transfer bycatch pressure from seabirds onto other vulnerable bycatch species such as sharks and turtles. Further research is needed to evaluate the effect of setting time on target fish catch and bycatch rates of seabirds, sharks and turtles.
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