Action: Set longlines at night to reduce seabird bycatch
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- Six out of eight studies from fisheries around the world found lower rates of seabird bycatch on longlines set at night, compared with during the day, or with previously collected data. However, effects seemed to depend on the species caught.
- Two studies found higher rates of bycatch on night-set longlines, due to high numbers of white-chinned petrels Procellaria aequinoctialis or northern fulmars Fulmarus glacialis being caught at night.
Most seabirds feed during the day and so longlines set at night may catch fewer birds. Some species, however, do hunt at night and so night-setting is unlikely to be an effective mitigation measure. An adequate knowledge of bycatch species’ ecology is therefore important in determining whether to promote night-setting.
Many of the studies in this section do not explicitly say whether night-setting was done for conservation purposes or not. However, given the valuable information they contain, we have included them below.
Supporting evidence from individual studies
A study using data from bluefin tuna Thunnus thynnus boats operating off New Zealand between 1988 and 1992 (Murray et al. 1993) found that the effects of night-setting on seabird bycatch rates varied between fishing areas, probably due to different species making up the majority of bycatch. In southern areas, 87% of 47 identified birds caught were albatrosses and 73% of 88 birds were caught between 0600 and 1400 (when 41% of 1,009 lines were set). In contrast, in northern fishing grounds, where 59% of 75 identified birds were petrels, 44% of the 181 birds caught were hooked within 90 minutes of dawn or dusk and 42% were caught at night (when 54% of 1,180 lines were set).
A small study on a commercial longlining boat in the South Atlantic in March-April 1993 (Ashford et al. 1994) found that no birds were caught on seven lines, set predominantly at night. The number of birds following the boat increased during the day: seven birds were seen following the boat during setting before 05:00 hr (first light was at 04:00 hr), with 84 being seen between 05:00 hr and 07:30 hr and several hundred following the boat during daytime hauling operations. This study also investigated the impact of streamer lines (see ‘Use streamer lines to reduce seabird bycatch on longlines’).
A replicated, controlled study on a commercial fishing boat in the South Atlantic in April-May 1994 (Ashford et al. 1995) found that longlines set at night appeared to catch fewer birds as bycatch, and of fewer species, compared to lines set during the day (15 birds caught on 16 lines set at night, all white-chinned petrels Procellaria aequinoctialis vs. 83 birds of six species on four lines set during the day). A further four day-set and three night-set lines caught 1-5 birds each but were not analysed separately. The vessel was fishing for Patagonian toothfish Dissostichus eleginoides off South Georgia, UK. This study is also discussed in ‘Use streamer lines to reduce seabird bycatch on longlines’ and ‘Use a sonic scarer when setting longlines to reduce seabird bycatch’.
A replicated and controlled study (Cherel et al. 1996) in the Patagonian toothfish Dissostichus eleginoides fishery in the South Atlantic found that 38 birds (two grey-headed albatross Thalassarche chrysostoma, formerly Diomedea chrysostoma, and 36 white-chinned petrels Procellaria aequinoctialis) caught on 72 longlines (174,000 hooks) set in February 1994, were caught at a much higher rate on lines set at night, than during the day (1.00 vs. 0.38 birds/1,000 hooks). The study took place around South Georgia (UK) and Kerguelen Islands (France) (sectors 332 and 333). This study is also discussed in ‘Turn decklights off during night-time setting of longlines to reduce bycatch’.
A study in March-May 1997 near South Georgia, South Atlantic (Ashford & Croxall 1998) found that 61 line sets, laid at night from a Patagonian toothfish Dissostichus eleginoides vessel, caught a total of 12 birds. This was the equivalent of 0.1 birds/1,000 hooks, which the authors’ state is considerably lower than many boats fishing near South Georgia, possibly due to night-setting of lines. Nine birds were white-chinned petrels Procellaria aequinoctialis, two black-browed albatross Thalassarche melanophrys and one was unidentified.
A replicated, controlled study using data from 86 longlining vessels operating in Australian waters, between April 1992 and March 1995 (Klaer & Polacheck 1998) found that longlines set at night caught approximately five times fewer seabirds than those set during the day (1.0 birds/1,000 hooks for 924 line-sets set at night vs. 4.8 birds/1,000 hooks for 1,372 line-sets set during the day). The difference was greatest on nights close to a new moon (with 7% of the bycatch rates of day sets), but there were always significant reductions (sets on full moon nights had approximately one-third the bycatch rates of day sets). This study does not discuss which birds were caught, but previous studies have shown that this fishery catches mainly albatross. This study is also discussed in ‘Use bait throwers to reduce seabird bycatch’ and ‘Thaw bait to reduce seabird bycatch’.
A replicated, controlled study in the sub-Antarctic Indian Ocean in 1994-7 (Weimerskirch et al. 2000) found that longlines set at night had significantly lower seabird bycatch, compared to those set during the day (0.91 birds caught/1,000 hooks for day-set lines vs. 0.17 birds/1,000 hooks for night-set lines, total of 524 lines studied). This result was consistent across all species, except for wandering albatross Diomedea exulans, which was only caught on 12 occasions. The authors note that whilst the number of white-chinned petrels Procellaria aequinoctialis caught was half that caught during the day, these levels may still be unsustainably high: they quote an unpublished figure of 340 petrels caught during a single line set off Kerguelen Island. The study took place on three Ukranian and one Japanese longliners fishing for Patagonian toothfish Dissostichus eleginoides off Kerguelen Island (France). Deck lights were not switched on during night setting. This study is also discussed in ‘Use streamer lines to reduce seabird bycatch on longlines’ and ‘Reduce seabird bycatch by releasing offal overboard when setting longlines’.
A replicated and controlled study (Melvin et al. 2001) in the North Pacific in late summer 1999 and 2000, found that lines set at night or during sunrise had higher rates of seabird bycatch (0.13 and 0.07 birds/1,000 hooks respectively) than those set during the day or at sunset (0.02 and 0.01 birds/1,000 hooks respectively). Differences were due to bycatch rates of northern fulmars Fulmarus glacialis (the most numerous species caught and the only species caught at night). Shearwaters Puffinus spp. constituted 67% of species caught during the day, but were never caught during the night. A total of 490 line sets were studied from the Pacific cod Gadus macrocephalus and walleye pollock Theragra chalcogramma fishery southeast of the Pribilof Islands, USA. This study is also discussed in ‘Weight baits or lines to reduce longline bycatch of seabirds’, ‘Use streamer lines to reduce seabird bycatch on longlines‘, ‘Use a line shooter to reduce seabird bycatch’ and ‘Set lines underwater to reduce seabird bycatch’.
- Murray T.E., Bartle J.A., Kalish S.R. & Taylor P.R. (1993) Incidental Capture of Seabirds by Japanese Southern Bluefin Tuna Longline Vessels in New Zealand Waters, 1988-1992. Bird Conservation International, 3, 181-210
- Cherel Y., Weimerskirch H. & Duhamel G. (1996) Interactions between longline vessels and seabirds in Kerguelen waters and a method to reduce seabird mortality. Biological Conservation, 75, 63-70
- Klaer N. & Polacheck T. (1998) The influence of environmental factors and mitigation measures on by-catch rates of seabirds by Japanese longline fishing vessels in the Australian region. Emu, 98, 305-316
- Weimerskirch H., Candeville D. & Duhamel G. (2000) Factors affecting the number and mortality of seabirds attending trawlers and long-liners in the Kerguelen area. Polar Biology, 23, 236-249
- Melvin E.F., Parrish J.K., Dietrich K.S. & Hamel O.S. (2001) Solutions to seabird bycatch in Alaska's demersal longline fisheries. Washington Sea Grant Program, University of Washington report.