Use streamer lines to reduce seabird bycatch on longlines
Overall effectiveness category Beneficial
Number of studies: 16
Background information and definitions
Streamer lines are long lines attached to a high point on the stern of a fishing boat so that they fall slowly to the surface of the water. On the 25 m or so of the lines, multiple ‘streamers’ are attached: strands of often brightly coloured line attached on a swivel to the main line. These move in the wind and interfere with birds attempting to reach the baited longline below. Streamer lines can vary in effectiveness with design, and the Commission for the Conservation of Antarctic Marine Living Resources (CCAMLR) and some other fisheries organisations have specific recommendations on their design. For example, boats in CCAMLR fishing areas must use a line at least 150 m long, attached 4.5 m above the water, with five sets of streamers attached at 5 m interval (Miller et al. 2003).
Multiple streamer lines may also be more effective than a single streamer, and how the streamer is deployed is thought to be important: if the wind moves the streamer so it is not directly over the longline then it is unlikely to have an effect.
Miller, D.G.M., Sabourenkov, E.N. and Ramm, D.C. (2003) CCAMLR’s approach to managing Antarctic marine living resources. Conference Reports of: Deep Sea 2003: Conference on the Governance of Deep-sea Fisheries, Queenstown, New Zealand.
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.Study and other actions tested
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.Study and other actions tested
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.Study and other actions tested
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.Study and other actions tested
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’.Study and other actions tested
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.Study and other actions tested
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.Study and other actions tested
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’.Study and other actions tested
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.Study and other actions tested
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’.Study and other actions tested
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.Study and other actions tested