TITLE:
The Development and Operational Testing of an Underwater Bait Setting System to Prevent the Mortality of Albatrosses and Petrels in Pelagic Longline Fisheries
AUTHORS:
Graham Robertson, Phillip Ashworth, Peter Ashworth, Ian Carlyle, Steven G. Candy
KEYWORDS:
Seabird Bycatch, Longline Fisheries, Underwater Setting, Marine Engineering, Innovation, Co-Operative Research
JOURNAL NAME:
Open Journal of Marine Science,
Vol.5 No.1,
December
22,
2014
ABSTRACT: Longline fisheries for tunas and tuna-like species present an
existential threat to many populations of albatrosses and petrels worldwide. To
prevent this form of mortality we developed a new technology designed to deploy
baited hooks underwater beyond the dive depths ofseabirds (6 - 10 m for the species most commonly caught). The
underwater bait setter is a stern-mounted, hydraulically-operated and
computer-controlleddevice that catapultsbaited hooks underwater in a steel capsuleconnected to hydraulic winches
by Spectra® rope. Baits are flushed from the capsule by water pressure
through a spring-loaded bait release door. The chief engineering challenges in
the developmental stageswere ensuring:1) bait deliveryto target depths with cycle times (time from release to
recovery) that were practical for fishing operations;2) bait retention in the
capsule (no drop-outs) on the descent phase of the cycle;3) baits, uponrelease at target depth, were
not drawn up the water column on the capsule recovery phase (from possible
hook-ups and/or suction); and4) the retention of baitsonhooks post-release from the capsule was not affected by the
mechanical release underwater. Operational trials with the final version of the
capsule yieldedsatisfactory cycle times to depths of 6 - 10 m. All baits
were retainedin the capsule on the descent andreleased as requiredat target depths (n = 606
deployments). Bait retention on hooks post release from the capsule and
retention on hooks hand-set at the surface (the conventional method) were
statistically indistinguishable.The underwater bait setter is modular in construction and can
be fitted to all types of vessel sterns.