Best practice seabird bycatch mitigation for pelagic longline fisheries targeting tuna and related species

Seabird bycatch in the tuna and billfish longline fishery in South African waters has had one of the highest seabird bycatch rates in the world. Research was carried out aboard two Japanese longline vessels in the South African EEZ in 2010. Half of the branch lines on each vessel were weighted using the double-weight configuration, which consists of a weighted section that was inserted into the monofilament section of a branch line 2m above the hook. Each vessel also deployed two "hybrid" bird-scaring lines during every set. the lines had a mix of long and short streamers. The rate of bird attacks on baited hooks was four times higher on unweighted lines. Mortality of seabirds on weighted branchlines combined with bird-scaring lines was six times less than on unweighted lines. The rate of seabird bycatch was more than 13 times higher during the day than at night. The authors conclude that the combination of two bird-scaring lines, weighted branch lines, and night setting qualify as best practices for seabird bycatch mitigation for fleets targeting tuna and related species in the South African EEZ.