Long Line Fishing

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

Dr. Graham Robertson

Australian Antarctic Division; Hobart, Australia

The underwater bait setter

Seabirds, such as albatrosses and petrels, die when they dive on baited hooks set from longline vessels, become hooked or entangled in gear, drawn underwater and drown. Mortality on longlines is depleting populations of seabirds worldwide, and some populations are decreasing at an alarming rate. Despite recent dramatic reductions in mortality in longline fisheries operating in the southern oceans of the world (which provides hope conservation efforts will succeed elsewhere), some populations continue to decrease due to longline fisheries in sub tropical regions of the world. This is where tuna and swordfish fisheries operate. To help make these fisheries seabird safe Amerro Engineering (Queensland, Australia) and the Australian Antarctic Division have developed a new technology, called the underwater bait 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 freefalls in 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 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 1-3.

Figure 1. The latest configuration of the MK1 underwater setting machine being trialed off eastern Australian in January 2010. The hydraulics and control box are mounted on the roof to reduce the number of pulleys involved in connecting the hydraulics motors to the capsule. Fewer pulleys increase the transfer of energy from hydraulic motors to the capsule, which increases depths attained for a given cycle time.

Figure 2. The drive system of the underwater setter. Shown are the control box (houses the PLC, data recorder and GPS; A), recovery motor (B), solenoid and relays (C) and pull-down motor (D). The on/off button and brake and timer are on the other side. The pulleys holding the spectra rope are barely visible beneath the hydraulic motors.

Figure 3. Operating the machine involves two steps – placement of baited hook in capsule and firing the release button on cue from vessel audio beep timer. The release button is the small cylindrical object beneath and slightly to the right of the deckhands elbow.

Potential benefits

© Graham Robertson

The underwater setter has the potential to:

  • Eliminate the mortality of surface-seizing species such as albatrosses and reduce – or even eliminate – mortality of deep diving species such as white-chinned petrels, grey petrels and shearwaters,
  • Eliminate bait loss to seabirds,
  • Permit fishing at any time of the day/night cycle,
  • Remove the threat of seasonal closures to protect seabirds, including in seasons when attacks are most intense,
  • Permit fishing with line weighting regimes that might be considered to be more acceptable to fishing industries,
  • Facilitate data collection on various aspects of fishing operations of importance to the fishing industry, government fisheries management agencies and working groups responsible for monitoring seabird by-catch,
  • Reduce the need for onboard independent fisheries observers to monitor compliance with mitigation requirements. Courtesy of the PLC operational data can be written to duplicated camera SD cards in the control box and downloaded via USB to the computer on each return to port. This information can be used to assess compliance to requirements to set gear with the underwater setter. If proven to be successful in deterring seabirds, the underwater setter will be one of the few mitigation devices that incorporates compliance as a design feature (others: night setting on VMS-equipped vessels; leaded swivels in pelagic branch lines; demersal longlines with integrated weight).

The next steps

Work in 2011 will culminate in a “proof-of-concept” experiment in the Uruguayan pelagic longline fishery in collaboration with the Uruguayan government and the Uruguayan fishing industry. The experiment will occur in Uruguay because of the high abundances of difficult-to-deter seabirds in Uruguayan waters and because of the strength of the partnership between Australia and Uruguay with this project. Plans for 2011 are:

© Graham Robertson

  • Collaborate with Uruguayan colleagues in Australia to ensure that the Mk2 version of the underwater setter (when built) will be suitable for Uruguayan vessels and sea conditions. This exercise was completed in January 2010.
  • Collaborate with Uruguayan colleagues in Uruguay to enable engineers responsible for the design and construction of the underwater setter to gain familiarity with the fishing vessel chosen for the experiment. Scheduled for April 2010.
  • Build the Mk version of the machine and ship to Uruguay in June 2010,• equip Uruguayan vessel with machine and conduct in-shore trials on performance. Scheduled for July 2010.
  • Complete bait retention of hooks trial on vessel in Uruguay,
  • Complete bait retention in capsule on vessel in Uruguay. This trial, along with that on bait retention on hooks, is designed to provide proof that baits are deployed at target depths and that bait retention on hooks is not affected by deployment underwater,
  • Conduct the proof of concept experiment on the fishing grounds in Uruguay. This experiment is scheduled for May/June 2011.

In addition, we will continue to work with the MK1 version of the machine at sea in Australia. The intention is to deploy a large number of hooks (> 150,000) to test the reliability and durability of the machine under production fishing conditions.

Once this work has been completed, the underwater bait setter will be available for longline fishermen to adopt. We will work with fisheries management agencies in various countries to facilitate uptake, and continue to work with international funding bodies to help fishermen purchase the machine (on a price share basis) in fisheries that are critical to the conservation of seabirds worldwide.

The total estimated cost of this project is $200,000 over the next year. Find out how you can help by clicking on the button to our Crowdrise page below.

Thank you to all of our wonderful sponsors: