This description relies upon:
Birdlife International. 2014. Bycatch Mitigation Fact-sheet 11 (September 2014), Pelagic Longline: Bait caster and line shooter.
A line shooter is a hydraulically operated device designed to deploy the mainline at a speed faster than the vessel’s forward motion, which removes tension from the longline. This allows the mainline to enter the water immediately astern of the vessel, rather than up to 30 m behind the vessel. It has been demonstrated that variation in tension on the mainline will affect the sink rates of baited hooks and therefore the risks to seabirds.
Effectiveness at reducing seabird bycatch
Research in the Australian tuna fishery has revealed that setting mainline loose with a line shooter resulted in slower sink rates of baited hooks in surface waters compared to baited hooks attached to mainline set without a line shooter (Robertson et al., 2010). The most likely reason for this is that propeller turbulence slowed the sink rates of loose mainlines which, in turn, slowed the sink rates of baited hooks. Although tests against seabirds are required, this result suggests that mainline set loose with a line shooter is likely to increase (not decrease) the risk to seabirds during line setting operations. Regarding the actual fishing (soak) period, baited hooks attached to loose mainlines settle deeper in the water column than hooks attached to mainlines set without a line shooter, which may affect accessibility to diving seabird species. However, the evidence to date suggests the primary - if not all - interactions occur immediately after line setting when baited hooks are clearing surface waters. Until evidence to the contrary is produced it should not be considered that line shooters reduce exposure of baited hooks to seabirds.
Best practice recommendations (see 'Important Note' below)
Line shooters should not be considered a seabird bycatch mitigation measure (Robertson et al., 2010). If used to improve fishing efficiency, line shooters should be used with a suite of mitigation measures, including:
- Streamer lines
- Line weighting
WCPFC CMM-2012-07 Conservation and Management Measure to Mitigate the Impact of Fishing for Highly Migratory Fish Stocks on Seabirds states that "deep setting line shooters" must be employed in conjunction with at least one other mitigation measure. They are not regarded as a sufficient mitigation measure on their own. If used, a mainline shooter must be mounted at least 1m forward of the stern. They must also be deployed in a manner such that the hooks are set substantially deeper than they would be lacking the use of the line shooter, and such that the majority of hooks reach depths of at least 100 m. See the CMM for specific requirements.
- Birdlife International. 2014. Bycatch Mitigation Fact-sheet 11 (September 2014), Pelagic Longline: Bait caster and line shooter.
- Brothers, N.P., Cooper, J. and Lokkeborg, S. 1999. The incidental catch of seabirds by longline fisheries: worldwide review and technical guidelines for mitigation. FAO Fisheries Circular No. 937. Food and Agriculture Organization of the United Nations.
- Robertson, G., Candy, S. and Wienecke, B. 2010. Effect on line shooter and mainline tension on the sink rates of pelagic longlines and implications for seabird interactions. WCPFC-SC6-EB-WP-07.
- Robertson, G., Candy, S.G. and Wienecke, B. 2010. Effect of Line shooter and mainline tension on the sink rates of pelagic longlines and implications for seabird interactions, Aquatic Conservation: Marine and freshwater ecosystems. DOI: 10.1002/aqc.1100