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Providing evidence to improve practice

Action: Use streamer lines to reduce seabird bycatch on longlines Bird Conservation

Key messages

  • A total of eight studies and two literature reviews from coastal and pelagic fisheries across the world found strong evidence for reduced seabird bycatch on longlines when streamer lines were used.
  • A replicated, controlled trial from the sub-Antarctic Indian Ocean found no reduction in bycatch rates when using streamer lines, whilst five studies were inconclusive, uncontrolled or had weak evidence for reductions.
  • The effect of streamer lines appears to vary between seabird species: northern fulmars Fulmarus glacialis were consistently caught at lower rates when streamers were used but shearwaters Puffinus spp. and white-chinned petrels Procellaria aequinoctialis were caught at similar rates with and without streamers in one study each.
  • The three studies that investigated the use of multiple streamer lines all found that fewer birds were caught when two streamer lines were used, compared to one, with even fewer caught when three were used.


Supporting evidence from individual studies


A controlled study on a fishing voyage off the southwest coast of Tasmania, Australia (Brothers 1991), found that using a streamer line reduced the number of baits taken by albatross from 5.8/1000 to 1.7/1,000. Fewer attempts at baits were also made within 50 m of the ship (from 12.8/1,000 baits and 63% of the total attempts to 0.2/1,000 baits and 2.3%). Streamer lines were 150 m long with seven ‘double-line vertical streamers’ attached at 4.1 m intervals.



A comparative study of ten bluefin tuna Thunnus thynnus longlining boats fishing off New Zealand in 1992 (Murray et al. 1993), found that none of five vessels that used a streamer line over 51% of the time caught any birds (over 100 line sets). The remaining five boats used streamer lines for less than 12% of the time and caught 14 birds over 157 sets. However, the authors cautioned that these results were preliminary, with limited observer coverage, no controls and no statistical tests.



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 for Patagonian toothfish Dissostichus eleginoides. The authors state that they could not draw conclusions on the effectiveness of the streamers because of the small number of repeats and the lack of birds interacting with line setting. This study also investigated the impact of setting lines at night (see ‘Set longlines at night to reduce seabird bycatch’).



A study of 20 longlines set in April-May 1994 in the South Atlantic (Ashford et al. 1995) found that 98 birds were caught as bycatch on the lines, with 45 on two lines set without streamer lines, 38 on two set with a streamer line and 1-5 birds/line for seven set with a different streamer design. A further 15 birds (all white-chinned petrels Procellaria aequinoctialis) were caught on 15 sets, of which three used the first streamer design. The authors concluded that streamer lines ‘were observed to interrupt birds’ behaviour…and to reduce mortality’. A streamer line was also use during the hauling of seven line sets, but no birds were caught during hauling, either with or without streamer lines. This study is also discussed in ‘Set longlines at night to reduce seabird bycatch’ and ‘Use a sonic scarer when setting longlines to reduce seabird bycatch’.



Analysis of data from 14 longlining trips by 12 vessels in the South Atlantic between March and May 1995 (Moreno et al. 1996), found that seven vessels using streamer lines caught significantly fewer birds per unit fishing effort (BPUE < 0.1 birds/1,000 hooks) than those without streamer lines (BPUE > 0.3 birds/1,000 hooks). A total of 1,428 birds were caught. The authors note that there was considerable variation in BPUE due to confounding factors, but that line sets compared were similar apart from the use of streamers. Vessels were fishing for Patagonian toothfish Dissostichus eleginoides in Subarea 48.3 (South Georgia and the South Sandwich Islands).



A replicated, controlled study off the coast of Norway (Løkkeborg 1998) found that seabird bycatch on 13 days in May 1996 was significantly lower for 13 daytime line sets when a streamer line was used (two birds caught, 0.04 birds/1,000 hooks), compared to control sets with no streamer line (99 birds, 1.75 birds/1,000 hooks). Bycatch was mainly northern fulmars Fulmarus glacialis and the streamer line was 8 mm nylon with 8 cm wide, 0.5-3 m long yellow tarpaulin streamers at 5.1 m intervals.



A randomised, replicated and controlled study on a boat in the South Atlantic on 27 nights between March and May 1997 (Ashford & Croxall 1998), found that, when the vessel followed other guidelines from the CCAMLR streamer lines did not significantly reduce BPUE (a total of 12 birds were killed by lines). However, the authors predict that 125 replicates of each treatment would be needed to detect the effect of streamer lines, far more than in this study. The vessel was fishing for Patagonian toothfish Dissostichus eleginoides in Subarea 48.3 of the southwest Atlantic (South Georgia and the South Sandwich Islands), setting an average of 12,990 hooks each night. CCAMLR guidelines say that lines should be set at night and weighted, that deck lights should be extinguished and no offal discarded during line setting.



An analysis of data from tuna vessels fishing in Australian waters in 1991-5 (Brothers et al. 1999) does not provide conclusive evidence for the effectiveness of streamer lines. Voyages with streamer lines caught more birds than those without, but when catch rates for individual seasons and areas were analysed, catch rates were lower with streamer lines, but not significantly so. The authors argue that the lack of conclusive evidence is due to the lack of a controlled analysis and the disproportionate use of streamer lines in areas with higher catch rates and during the day (see ‘Set longlines at night to reduce seabird bycatch’). A total of 3,477 line sets were studied.



A replicated, controlled study in the sub-Antarctic Indian Ocean in 1994-7 (Weimerskirch et al. 2000) found that using a streamer line whilst setting longlines did not appear to reduce seabird bycatch for all species combined, or for white-chinned petrels Procellaria aequinoctialis, the most frequently caught birds (0.57 birds/1,000 hooks on sets with a streamer vs. 0.52 birds/1,000 hooks for sets without, total of 524 lines studied). Streamer lines were 150-175 m long propylene ribbons (2 m long) every 2-3 m. This study is also discussed in ‘Set longlines at night to reduce seabird bycatch’ and ‘Reduce seabird bycatch by releasing offal overboard when setting longlines’.



A randomised, replicated and controlled experiment in February 1999, in the Northwestern Islands, Hawaii, USA (Boggs 2001), found that using a streamer line when setting hookless bait lines lowered attacks by black-footed Phoebastria nigripes and Laysan P. immutabilis albatrosses by 75% and 77% respectively, compared to controls. Streamer lines were 150 m long: a 10 m attachment section of 6.25 mm twisted yellow polypropylene; 40 m with seven forked ‘aerial streamers’; 85 m of red 3 mm nylon with eight small streamers in the first 40 m, 15 m of 12 mm yellow polypropylene. Lines were attached 8 m above the stern so that the first streamer touched the water approximately 5 m behind the bait entry point. Twenty four repeats of each treatment were used, with lines set during the day, mimicking swordfish longline techniques.



A randomised, replicated and controlled experiment off the coast of mid-Norway in August 1998 (Løkkeborg 2001), found that two streamer lines both significantly reduced the seabird bycatch on longlines compared with lines set with no streamer (no birds caught with the 11 repeats using the advanced streamer, two birds and 0.03 birds/1,000 hooks with the 11 repeats of the simple streamer vs. 74 birds and 1.06 birds/1,000 hooks for 11 sets with no streamer line). The majority of hooked birds were northern fulmars Fulmarus glacialis. Each set contained approximately 6,500 hooks and was set during daylight. Both streamers were 80 m long and hung 7-8 m above sea level; the advanced line had four gillnet float rings at the trailing end and twelve 8 cm wide yellow tarpaulin streamers, 5 m apart, 0.5-3 m long; the simple line had a punctured buoy at the trailing end and six, equally placed, 30 cm, red plastic streamers.



Two randomised, replicated and controlled trials in 1999 and 2000 (Melvin et al. 2001) found that seabird bycatch was 88-100% lower on longlines set with paired streamer lines, compared to controls (0.00-0.04 birds/1,000 hooks with paired streamers vs. 0.22-0.37 birds/1,000 hooks for controls). Similarly, bycatch was lower with single streamers in the Pacific halibut Hippoglossus stenolepis and sablefish Anoplopoma fimbria fishery in the Gulf of Alaska and the Aleutian Islands, USA (0.01 birds/1,000 hooks), although reduction for paired streamers were higher (50% and 80% reductions in Laysan albatross Phoebastria immutabilis and northern fulmar Fulmarus glacialis bycatch, respectively). However, in the Pacific cod Gadus macrocephalus and walleye pollock Theragra chalcogramma fishery southeast of the Pribilof Islands, USA, lines set with single streamers caught as many birds as controls. This was due to similar numbers of shearwaters Puffinus spp. caught on lines with single streamers; no northern fulmars Fulmarus glacialis were caught on lines set with streamers. Streamer lines were 90 m of 21 mm blue polyester, with streamers of 6.4 mm orange tubing attached at 5 metre intervals for the first 50 m. This study is also discussed in ‘Weight baits or lines to reduce longline bycatch of seabirds’, ‘Set longlines at night to reduce seabird bycatch‘, ‘Use a line shooter to reduce seabird bycatch’ and ‘Set lines underwater to reduce seabird bycatch’.



A study on a longlining vessel on the Chatham Rise, New Zealand, in July-August 1998 (Smith 2001) and using weighted lines (see ‘Weight baits or lines to reduce longline bycatch of seabirds’) and a streamer line caught an average of 0.0093 birds/1,000 hooks – far lower than many other studies. The streamer line extended 75-85 m behind the boat, covering the longline to a depth of 2-5 m. Many seabirds can dive up to 10 m (a depth not reached until 170 m behind the streamer), so the authors caution that the streamer may not offer as high protection as it appeared.



A randomised, replicated and controlled trial on a commercial longlining vessel off the coast of mid-Norway in August 1999 (Løkkeborg & Robertson 2002), found that bycatch of northern fulmar Fulmarus glacialis fell to zero when a streamer line was deployed during line setting and just one bird (0.02 birds/1,000 hooks) when both a streamer line and line shooter were used, compared with 32 fulmars (0.52 birds/1,000 hooks) during control line sets, and 13 fulmars (0.22 birds/1,000 hooks) when just a line shooter was used. Eleven repeats of each treatment were used, with lines set during daylight. Streamer lines were 90 m long, with a 69 m streamer section with twelve 8 cm wide yellow tarpaulin streamers, 5.4 m apart, 0.5-2 m long. This study is also discussed in ‘Use a line shooter to reduce seabird bycatch’.



A literature review of three replicated and controlled studies off the coast of Norway (Løkkeborg 2003), found that only two northern fulmars Fulmarus glacialis were caught on 185,000 longline hooks when a streamer line was deployed, compared with 205 birds (mostly fulmars) from a similar number of hooks without streamer lines. The three studies (6, 11, 14) are outlined in detail above.



A literature review (Melvin et al. 2004) described evidence for the effectiveness of bycatch reduction methods in pelagic longline fisheries as ‘inconclusive’, highlighting the need for further research into the design and configuration of streamer lines. Two studies (one controlled) from Alaska and the Falkland Islands found that streamer lines reduced seabird mortality by 71% (single line), 75% (two lines) or 97% (three lines). An uncontrolled study near New Zealand suggests that using two streamer lines and an acoustic cannon almost eliminated white-chinned petrels Procellaria aequinoctialis diving within 50 m of the boat, but that the ‘boom and bridle’ system of attaching streamers to boats did not reduce diving within the aerial range of the streamer line.


Referenced papers

Please cite as:

Williams, D.R., Child, M.F., Dicks, L.V., Ockendon, N., Pople, R.G., Showler, D.A., Walsh, J.C., zu Ermgassen, E.K.H.J. & Sutherland, W.J. (2018) Bird Conservation. Pages 95-244 in: W.J. Sutherland, L.V. Dicks, N. Ockendon, S.O. Petrovan & R.K. Smith (eds) What Works in Conservation 2018. Open Book Publishers, Cambridge, UK.