Night / day setting

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 [11]. In contrast, Taiwanese, Chinese and Australian longliners have used shallow setting at night in some areas to target large bigeye tuna [3]. 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 Decisions database).

The effects of time of set, soak and haul on bycatch levels become more complicated when set, soak and haul fall in both day and night, that is, including either dawn or dusk.
 
Night setting is a proven bycatch reduction technique for many seabird assemblages, when used in conjunction with other mitigation techniques. However, for marine turtles and sharks and rays, it is unclear how manipulating time of set, soak or haul could reduce bycatch. A recent review (2012) of marine mammal bycatch reduction techniques found only one study that had looked at night setting; it was unsuccessful [10].
 
Seabirds
 
This description relies upon: Birdlife International. 2014. Bycatch Mitigation Fact-Sheet 5 (September 2014), Demersal and Pelagic Longline: Night-setting.
 
Night-setting requires no modification of fishing gear. It simply requires setting to be started and finished during the hours of darkness, between nautical dusk and dawn. Setting at night avoids periods when most seabirds are actively foraging. Available information suggests that albatrosses and petrels detect food items at close range by sight and so darkness effectively conceals baited hooks from most foraging seabirds.  Additionally, many seabirds, particularly albatrosses, are most active during daylight hours, including dusk and dawn. Data from stomach temperature gauges [15] suggest that wandering albatross, at least, feed primarily during daylight hours and rest at night. This is reflected in bycatch studies, which frequently show that time of day is an important factor affecting the number of birds caught during longline setting [1]. In particular, dawn and dusk are times when birds are most active and consequently most vulnerable to longline bycatch [e.g. 2].
 
Effectiveness at reducing seabird bycatch
On moonless cloudy nights, night-setting can be highly effective at limiting seabird bycatch. However, for up to two weeks every month the moon may provide enough light to significantly reduce the effectiveness of night-setting [12,13].
 
Seabird species
The effectiveness of night-setting is also dependent on the species assemblage. In some instances, where albatrosses compose the majority of bycatch, night-setting can effectively reduce seabird bycatch. Around the Prince Edward Islands, Southern Ocean, experimental trials indicate albatross bycatch rates are ten times higher during the day than at night whereas white-chinned petrel bycatch was halved when setting at night [14]. Off the east coast of Australia, where shearwaters predominate, night-setting alone is less effective, although bycatch rates are still lower than day sets [1].
 
ACAP best practice advice
To be effective, vessels should not commence line setting until at least one hour after nautical dusk and should complete setting at least one hour before nautical dawn. Combined with night setting, deck lights 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.
 
Potential problems and solutions
Night-setting is only truly effective on dark nights (i.e. the new moon half of the lunar cycle). On clear nights with a full moon, night-setting becomes far less effective [12,13].
- In the highest latitudes during the summer months, the time between nautical dusk and dawn is limited. In these circumstances, fishing opportunities are greatly reduced. Careful planning is required to minimise the amount of lost time and the associated cost of lost fishing potential and fuel.
- Depending on the target species, the time of setting may have consequences for the catch rate of target species. This is more likely to be an issue in pelagic longlines where many species undergo daily vertical migrations.
 
Combinations of measures
Due to variations in the lunar cycle and the ability of some species to forage at night, night-setting is not an effective measure when used in isolation. It is recommended that night-setting is used in combination with a selection of other measures:
- Line weighting
- Streamer line
- Blue-dyed bait (squid)
 
Marine Turtles
 
The effect of time of set, soak or haul on marine turtle interactions with longlines has not been well studied. A recent (2014) review [6] found the following:
 
"A number of older and often unpublished studies explored the effects of soak duration and time of hauling on sea turtle interaction rates. However, owing to a lack of definitive results, as well as perhaps the negative ramifications for target species, these operational modifications have not been subject to further research or regulatory implementation. For example, Gilman et al. (2006) review two studies, one that found higher interaction rates at night (but was confounded with shallow setting) and another that found an effect of total (not daylight) soak time on loggerheads only.
 
While there may be further potential for mitigation through manipulation of soak duration and time of hauling (Gilman, 2011), issues of experiment design and inter- and intra-specific differences have led to conflicting results thus far and no clear research agenda."
 
Sharks
 
The biology and behaviour of elasmobranch species vary greatly and affect their chances of interacting with longline fishing gear. Both hook deployment depth and timing of the set and the haul (day versus night) have been found to affect 'catch per unit effort' (CPUE), perhaps due to different temperature preferences by each species [8]. For example, catch rates of bigeye thresher Alopias superciliosus in the Marshall Islands tuna longline fishery were highest on shallow night sets and deep day sets, which is consistent with this species’ movement pattern of swimming closer to the surface at night than during the day [5].  
 
Research considering elasmobranchs and time of set, soak or haul has been limited and not led to management recommendations. As time of set, soak or haul and soak duration have been studied together, refer to 'Soak duration' for more detail.
Ease of Deployment and Safety
Seabirds
Night-setting can raise concerns over crew safety. This can be overcome by ensuring adequate deck lighting is in place.
Compliance
Seabirds
Requires VMS (satellite transmitter), and other electronic monitoring of fishing activity or fishery observers. Vessel speed and direction vary between transiting, line setting, line hauling and when vessels are stationary on fishing grounds. VMS derived assessment of vessel activity in relation to the time of nautical dawn and dusk is considered acceptable for implementation monitoring.
Further Research
Seabirds
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.
References
  1. Baker, G.B. and Wise, B.S. 2005. The impact of pelagic longline fishing on the flesh footed shearwater Puffinus carneipes in Eastern Australia. Biological Conservation 126: 306-316.
  2. Belda, E.J. and Sanchez, A. 2001. Seabird mortality on longline fisheries in the Western Mediterranean: factors affecting bycatch and proposed mitigating measures. Biological Conservation 98: 357-363.
  3. Beverly, S., Robinson, E. and Itano, 2. 2004. Trial setting of deep longline techniques to reduce bycatch and increase targeting of deep-swimming tunas. 17th Meeting of the Standing Committee on Tuna and Billfish, Majuro, Marshall Islands, 9-18 August. FTWG-WP-7a.
  4. Birdlife International. 2014. Bycatch Mitigation Fact-Sheet 5 (September 2014), Demersal and Pelagic Longline: Night-setting.
  5. Bromhead, D., Clarke, S., Hoyle, S., Muller, B., Sharples, P. and Harley, S. 2012. Identification of factors influencing shark catch and mortality in the Marshall Islands tuna longline fishery and management implications. Journal of Fish Biology 80(5): 1870-1894. doi: 10.1111/j.1095-8649.2012.03238.x
  6. Clarke, S., Sato, M., Small, C., Sullivan, B., Inoue, Y. and Ochi, D. 2014. Bycatch in longline fisheries for tuna and tuna-like species: a global review of status and mitigation measures. FAO Fisheries and Aquaculture Technical Paper No. 588. Rome, FAO. 199 pp. http://www.fao.org/3/a-i4017e.pdf
  7. Gilman, E. 2011. Bycatch governance and best practice mitigation technology in global tuna fisheries. Marine Policy 35(5): 590-609.
  8. Gilman, E., Clarke, S., Brothers, N., Alfaro-Shigueto, J., Mandelman, J., Mangel, J.,  Petersen, S., Piovano, S., Thomson, N.,  Dalzell, P.,  Donoso, M., Goren, M. and Werner, T. 2008. Shark interactions in pelagic longline fisheries. Marine Policy 32(1): 1-18.
  9. Gilman, E, Zollett, E., Beverly, S., Nakano, H., Shiode, D., Davis, K.P., Dalzell, P. & Kinan, I. 2006. Reducing sea turtle bycatch in pelagic longline gear. Fish and Fisheries 7(1): 2-23.
  10. Hamer, D.J., Childerhouse, S.J. and Gales, N.J. 2012. Odontocete bycatch and depredation in longline fisheries: a review of available literature and of potential solutions. Marine Mammal Science 28(4): E345-E374.
  11. Jones, L. 2009. Hawaii Longliners Reduce Sea Turtle Bycatch. http://www.fws.gov/endangered/news/bulletin-summer2009/reduce-sea-turtle-by-catch.html
  12. Klaer, N. and Polacheck, T. 1998. The influence of environmental factors and mitigation measures on bycatch rates of seabirds by Japanese longline fishing vessels in the Australian region. Emu 98: 305-316.
  13. Petersen, S.L. 2008. Understanding and mitigating vulnerable bycatch in southern African longline and trawl fisheries. PhD thesis, University of Cape Town.
  14. Ryan, P.G. and Watkins, B.P. 2002. Reducing incidental mortality of seabirds with an underwater setting funnel. Biological Conservation 104: 127-131.
  15. Weimerskirch, H. and Wilson, R.P. 1992. When do wandering albatrosses forage? Marine Ecology Progress Series 86: 297-300.