Preliminary performance assessment of an underwater line setting device for pelagic longline fishing

Baited branchlines were set from a tuna longlining vessel using an underwat er setting device and their sink patterns compared with those of baited bra nchlines that were hand-thrown. Using a paired t-test at an hypothesised me an difference of 2 m, at a point 100 m astern of the vessel, baited branchl ines set using the device were significantly deeper than those that were ha nd-thrown. Baited branchlines set using both methods showed a high variatio n in their sink patterns; on some sets they sank faster than others. The un derwater setting device has potential to reduce seabird bycatch substantial ly with minimal intrusion on the normal operation of a longline fishing ves sel. It delivers baits underwater (removing the visual cue of a hand-thrown baited hook to seabirds) and immediately places baited hooks outside the d iving range of some vulnerable albatross species (Diomedea spp., Phoebastri a spp., Thalassarche spp., and Phoebetria spp.).