Progress report on the development and testing of the underwater bait setter for pelagic longline fisheries

1. This paper summarises recent progress and future work relating to the development, construction and testing of a device that sets hooks several metres underwater to avoid detection by seabirds. 2. The underwater setter is a stern-mounted hydraulically-driven device. It comprises components that are fixed to the vessel and a component (a capsule that holds the baited hook) that is driven down into the water column each time a hook is set. This design is the most fuel efficient method of delivering baited hooks at required depths underwater because it minimises the drag associated with devices that remain underwater while setting (e.g., underwater setting chutes). The device is modular and can be readily retrofitted to most tuna fishing vessels after their construction. THE UNDERWATER SETTER The underwater setter is a stern-mounted hydraulically-driven device that delivers baited hooks underwater to avoid detection by seabirds. It comprises components that are fixed to the vessel and a component (a capsule that holds the baited hook) that is driven down into the water column each time a hook is set. This design is the most fuel efficient method of delivering baited hooks at required depths underwater because it minimises the drag associated with devices that remain underwater while setting (e.g., underwater setting chutes). The device is modular and can be readily retro-fitted to most tuna fishing vessels after their construction. The underwater setter comprises a vertical track on the transom, bait-holding capsule, a box with hydraulics, relays and pulleys and a control box which houses a programmable logical controller (PLC). The PLC runs the system and records data. The capsule is mounted in a docking station and secured to the track by 5 mm spectra rope attached via pulleys to the hydraulic motors. To operate the device the deckhand simply places a baited hook in the bait chamber of the capsule and presses the release button. The pull-down motor propels the capsule down the track at >3 m/s. At the end of the track (extends ~ 1 m underwater but able to be varied to accommodate various sea states) the capsule freefalls to a pre-set depth. Depth attained is a function of capsule descent speed, capsule weight and cycle time. The cycle time is programmed into the PLC. At the end of the descent phase the PLC engages the recovery motor and the capsule returns to the start position. The baited hook is flushed from the capsule on the ascent phases through a spring loaded door at the bottom of the capsule. The cycle is repeated every 8 seconds. Target release depth can be varied from 4 m to > 8 m, depending on the diving capabilities of the species of seabirds interacting with gear. Ideally, releasing baited hooks beneath the lower limit of propeller turbulence will be sufficient to deter diving seabird species. Opaque water from the propeller masks the sinking bait. The leaded swivels (60-75 g) used in most southern hemisphere pelagic longline fisheries will ensure baited hooks continue to sink (at ~ 0.4 m/second) once released from the capsule. Various aspects of the design of the machine and its operation are shown in Figures 1-4.