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Ed Melvin (Washington Sea Grant and School of Aquatic and Fishery Sciences, University of Washington, Seattle, Washington, USA) and colleagues have published online in the journal Fisheries Research (for 2014) on best-practice mitigation for ACAP-listed albatrosses and petrels in Asian distant-water tuna fisheries.

The paper’s abstract follows:

“We comprehensively tested combinations of three primary mitigation measures in a pelagic longline fishery with one of the highest rates of interaction with what may be the world's most challenging seabird assemblage (dominated by Procellaria genus petrels), aboard fishing vessels typical of the Asian distant water fleet.  Multiple measures were used to compare the performance of weighted vs. unweighted branch lines set with two bird-scaring lines – hybrid lines with long and short streamers – during daytime and nighttime.  The weights used were a novel double-weight configuration.  Secondary attacks on baits brought to the surface by white-chinned petrels drove albatross mortality.  Regardless of time of day, weighted branch lines with two bird-scaring lines, deployed and maintained with an aerial extent of 100 m, reduced bird attacks by a factor of four, and secondary attacks and seabird mortality by a factor of seven, compared to unweighted branch lines, with little effect on fish catch rates and with no injuries to crew.  This combination yielded zero bird mortalities when gear was set at night.  We conclude that the simultaneous use of two bird-scaring lines, weighted branch lines and night setting meet our criteria for best-practice seabird bycatch mitigation for the joint-venture fleet targeting tuna and related species in the South African EEZ.  To be successful, the aerial extent of bird-scaring lines should be aligned with the distance astern that baited hooks sink beyond the foraging depth of the dominant seabird – in this case white-chinned petrels to a depth near 5 m.  Given that these measures were successful in one of the most challenging pelagic longline fisheries, they are likely to be widely applicable to pelagic longline fisheries using similar gear.”

A hooked White-chinned Petrel, photograph by Nicolas Gasco

See also a previous news item on the research project reported here.

References:

Melvin, E.F., Guy, T.J. & Read, L.B. 2013.  Reducing seabird bycatch in the South African joint venture tuna fishery using bird-scaring lines, branch line weighting and nighttime setting of hooks.  Fisheries Research 147: 72-82.

Melvin, E.F., Guy, T.J. & Read, L.B. 2014.  Best practice seabird bycatch mitigation for pelagic longline fisheries targeting tuna and related species.  Fisheries Research 149: 5-18.

John Cooper, ACAP Information Officer, 17 December 2013