Underwater setting techniques

Underwater setting techniques are means of deploying baited hooks below the surface of the sea, out of the sight and reach of foraging seabirds. They are unproven and not recommended as a mitigation method [1].
 
Examples of underwater setting techniques include:
- the underwater bait setter, also known as a bait setting capsule or underwater bait launcher; and
- underwater setting tubes or chutes.
 
While versions of the latter have been trialled in pelagic longline fisheries, they are currently used only in demersal longline fisheries (see Birdlife International Factsheet 6 Demersal Longline: Underwater setting chute) and are not discussed here. Likewise, underwater setting funnels or lining tubes apply to demersal longline fisheries.
 
The underwater bait setter for pelagic longline fisheries deploys a baited hook underwater through a stainless steel capsule. Development has progressed through several stages. The current Mk2 incorporates:
  • a demountable track (attaches to the transom) which extends 1.4 m underwater. The track is stored inboard when transiting to and from fishing;
  • the capability for the Skipper to set maximum depth and cycle time from the wheel-house; and
  • modular construction comprising a box with hydraulic motors and winches, de-mountable track section and electronic control system and data logger operated from the wheel-house.
Research to-date has shown that the underwater bait setter has no impact on catch rates of target and non-target fish. Preliminary evidence suggest that underwater setting to 10 m depth prevents albatross and petrel mortality without the need for other mitigation measures (e.g., night setting; bird scaring lines). There is evidence that a small, residual, mortality exist with hooks set at 6 m depth but more data is required on effects of hooks set to this depth (and to 8 m depth). The final proof-of-concept experiment is scheduled for the southern autumn and winter of 2014.
  
Note: Click on the web link found under 'More Information' to view a stylised drawing of the prototype underwater bait setter.
References
  1. ACAP. 2017. ACAP Review and Best Practice Advice for Reducing the Impact of Pelagic Longline Fisheries on Seabirds. In: ACAP - Tenth Meeting of the Advisory Committee. ACAP, Wellington, New Zealand.
  2. Birdlife International. 2009. Fact sheet 6 (Version 1) Demersal Longline: Underwater setting chute.
  3. http://www.birdlife.org/seabirds/downloads/FS_6_Demersal_LL_Underwater_setting_chute_final.pdf
  4. Brothers, N., Cooper, J., Lokkeborg, S., 1999. The incidental catch of seabirds by longline fisheries: worldwide review and technical guidelines for mitigation. FAO Fisheries Circular 937.
  5. Bull, L. 2006. A review of methodologies aimed at avoiding and/or mitigating incidental catch of seabirds in longline fisheries. WCPFC-SC2-EB-WP-5.
  6. Robertson, G. and Domingo, A. 2011. Progress report on the BS30 Underwater Bait Setter for pelagic longline fisheries. ACAP SBWG-4 Doc 6 Rev2.
  7. Robertson, G. And Hay, I. 2012. Progress report on the development and testing of the underwater bait setter for pelagic longline fisheries. WCPFC-SC8-EB-IP-02.