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Providing evidence to improve practice

Individual study: Paired streamer lines are most effective method to reduce bycatch in two North Pacific fisheries, single streamer lines, underwater setting tubes and weighting lines produce smaller reductions and line shooters increase rate of bycatch

Published source details

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.


This study is summarised as evidence for the intervention(s) shown on the right. The icon shows which synopsis it is relevant to.

Use a line shooter to reduce seabird bycatch Bird Conservation

A randomised, replicated and controlled study (Melvin et al. 2001) in the North Pacific in August 1999, found that using a line shooter significantly increased the number of birds caught, compared to controls (0.336 birds/1,000 hooks vs. 0.218 birds/1,000 hooks). Treatment had no effect on the number of birds following vessels, or the attack rate on baits. A total of 156 line sets were studied, set for Pacific cod Gadus macrocephalus and walleye pollock Theragra chalcogramma 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‘, ‘Set longlines at night to reduce seabird bycatch’ and ‘Set lines underwater to reduce seabird bycatch’.

 

Set lines underwater to reduce seabird bycatch Bird Conservation

A randomised, replicated and controlled study (Melvin et al. 2001) in a North Pacific fishery in August 1999 found that using a setting funnel (“lining tube”) reduced the number of seabirds caught on longlines, compared to controls (0.045 birds/1000 hooks vs. 0.218 birds/1000 hooks). However, this decline was only fewer northern fulmars Fulmarus glacialis being caught, with the bycatch rate of shearwater Puffinus spp. remaining constant. Overall, the number of birds following and the rate of attacks on baits were consistent across treatments, although attack rates by shearwaters were twice as high when using a setting funnel. The study took place in 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’, ‘Set longlines at night to reduce seabird bycatch‘, ‘Use a line shooter to reduce seabird bycatch’ and ‘Use streamer lines to reduce seabird bycatch on longlines’.

 

Weight baits or lines to reduce longline bycatch of seabirds Bird Conservation

Two randomised, replicated and controlled studies in 1999 (Melvin et al. 2001) found that seabird bycatch rates were significantly lower on weighted longlines, than on controls (0.052 and 0.234 birds/1,000 hooks for weighted lines vs. 0.218 and 0.371 birds/1,000 hooks for controls; totals of 156 and 121 line sets). However, results in one fishery (for Pacific cod Gadus macrocephalus and walleye pollock Theragra chalcogramma fishery, southeast of the Pribilof Islands, USA) were due purely to reductions in northern fulmars Fulmarus glacialis caught, with shearwater Puffinus spp. bycatch remaining constant. In the second fishery (for Pacific halibut Hippoglossus stenolepis and sablefish Anoplopoma fimbria in the Gulf of Alaska and Aleutian Islands, USA), removing the single line set with the highest bycatch (of 27 birds) made the reduction in bycatch non-significant. A further trial in 2000 found no birds were caught on weighted or unweighted lines set under a streamer line (see ‘Use streamer lines to reduce seabird bycatch on longlines’. Weighted lines had 4.5 kg weights every 90 m. This study is also discussed in ‘Use a line shooter to reduce seabird bycatch’, ‘Set longlines at night to reduce seabird bycatch’ and ‘Set lines underwater to reduce seabird bycatch’.

 

Set longlines at night to reduce seabird bycatch Bird Conservation

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’.

 

Use streamer lines to reduce seabird bycatch on longlines Bird Conservation

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’.