Set lines underwater to reduce seabird bycatch

Overall effectiveness category Trade-off between benefit and harms
Number of studies: 5
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How is the evidence assessed?

Effectiveness

61%
Certainty

50%
Harms

24%

Calculating overall effectiveness category

Background information and definitions

Most birds caught on longlines are caught when the lines are being set, after the bait has been attached to hooks but before they have sunk out of the reach of surface-feeding birds. If lines are set underwater then it may reduce the time they are available to birds and therefore reduce bycatch.

Study locations

Key messages

Four replicated and controlled studies and a literature review in Norway, South Africa and the North Pacific found reductions in northern fulmar Fulmarus glacialis, albatross and petrel bycatch rates when using an underwater setting funnel. Although one found a disproportionate number of albatross were caught during day line setting.
A replicated and controlled study found that underwater setting increased attack rates of shearwaters Puffinus spp. on longlines and did not reduce bycatch.

About key messages

Key messages provide a descriptive index to studies we have found that test this intervention.

Studies are not directly comparable or of equal value. When making decisions based on this evidence, you should consider factors such as study size, study design, reported metrics and relevance of the study to your situation, rather than simply counting the number of studies that support a particular interpretation.

Supporting evidence from individual studies

A randomised, replicated and controlled study off the coast of Norway (Løkkeborg 1998) found that seabird bycatch in May 1996 was significantly lower when an underwater setting funnel was used to set longlines (28 birds caught, 0.49 birds/1,000 hooks for 13 line sets) than in control sets without the funnel (99 birds caught, 1.75 birds/1,000 hooks for 13 line sets). Lines were set during daylight and bycatch was mainly northern fulmars Fulmarus glacialis.
Study and other actions tested
Referenced paper
Løkkeborg S. (1998) Seabird by-catch and bait loss in long-lining using different setting methods. ICES Journal of Marine Science, 55, 145.
A randomised, replicated and controlled experiment, with 11 repeats of each treatment (each approximately 6,500 hooks), off the coast of mid-Norway during daylight in August 1998 (Løkkeborg 2001), found that longlines set using an underwater setting funnel significantly reduced the number of seabirds caught compared with control lines, set without a funnel (six birds and 0.08/1,000 hooks vs. 74 birds and 1.75/1,000 hooks). The majority of hooked birds were northern fulmars Fulmarus glacialis.
Study and other actions tested
Referenced paper
Løkkeborg S. (2001) Reducing seabird bycatch in longline fisheries by means of bird-scaring lines and underwater setting. Pages 33-41 in: E. Melvin & J. Parrish (eds.) Seabird Bycatch: trends, roadblocks and solutions. Alaska Sea Grant, Fairbanks.
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’.
Study and other actions tested
Referenced paper
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.
A replicated, controlled study in a South African fishery, between 1998 and 2000 (Ryan & Watkins 2002) found that seabird bycatch in longline sets that used an underwater setting funnel was significantly lower than sets that did not use a funnel, both during the day (funnel: 2,255,150 hooks set, 23 petrels, 10 albatross killed, 0.015 birds/1,000 hooks; no funnel: 434,598 hooks set, 20 petrels, 1 albatross killed, 0.048 birds/1,000 hooks) and night (funnel: 317,503 hooks set, 3 petrels and no albatross killed, 0.009 birds/1,000 hooks; no funnel: 2,045,912 hooks set, 56 petrels, one albatross killed, 0.028 birds/1,000 hooks). However, a disproportionate number of albatrosses were killed during day-time sets using the setting funnel. The study took place in the Patagonian toothfish Dissostichus eleginoides fishery off the coast of the Prince Edward Islands.
Study and other actions tested
Referenced paper
Ryan P.G. & Watkins B.P. (2002) Reducing incidental mortality of seabirds with an underwater longline setting funnel. Biological Conservation, 104, 127-131.
A review of two randomised, replicated and controlled studies off the coast of Norway (Løkkeborg 2003) found that fewer northern fulmars Fulmarus glacialis were caught on longline hooks when an underwater setting funnel was used (34 birds and 0.08-0.49 birds/1,000 hooks) compared to control line sets (174 birds and 1.06-1.75 birds/1,000 hooks). Both papers are outlined above.
Study and other actions tested
Referenced paper
Løkkeborg S. (2003) Review and evaluation of three mitigation measures – bird-scaring line, underwater setting and line shooter–to reduce seabird bycatch in the north Atlantic longline fishery. Fisheries Research, 60, 11-16.

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. (2020) Bird Conservation. Pages 137-281 in: W.J. Sutherland, L.V. Dicks, S.O. Petrovan & R.K. Smith (eds) What Works in Conservation 2020. Open Book Publishers, Cambridge, UK.

Where has this evidence come from?

List of journals searched by synopsis

All the journals searched for all synopses

This Action forms part of the Action Synopsis:

Bird Conservation

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Use bait throwers to reduce seabird bycatch Action Link	Unknown effectiveness (limited evidence)	1	Synopsis Link
Reduce seabird bycatch by releasing offal overboard when setting longlines Action Link	Likely to be beneficial	2	Synopsis Link