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The preliminary results of collaborative research conducted on reducing bird bycatch in pelagic tuna fisheries have been recently published by the Washington Sea Grant.

The work entailed comparing the performance of two bird-scaring streamer (tori) lines: light lines with short streamers and one with both short and long streamers.  A secondary objective was to assess the value of weighting branch lines, summarized here.

 The research was carried out in South African waters by a team of USA and South African scientists, led by Ed Melvin of Washington Sea Grant of the University of Washington in Seattle, USA.  The collaborative nature of the project was enhanced by it being undertaken aboard two joint-venture Japanese fishing vessels.

 Preliminary findings showed that weighted branch lines (with "safe leads"; see www.fishtekmarine.com/safeleads.php) sank nearly three times faster than did unweighted branchlines.  Further, they sank to a 10-m depth considered beyond the reach of most diving seabirds within 100 m of the vessel's stern (and thus still within the reach of the bird-scaring line, as against unweighted branch line reaching a similar depth as much as 300 m behind the vessel, well away for the protection of the streamers.

Tuna branchlines weighted with safe-leads sink baited hooks quickly away from foraging seabirds. Photograph by Graham Robertson 

The value of weighting was emphasised by only two birds being killed on the weighted sets, compared to no less than 126 killed on unweighted lines.  This translates to rates of 0.070 and 0.975 birds killed/thousand hooks, respectively.  Significantly, there was no difference in catch rates of tuna and Swordfish between weighted and unweighted branch lines.

 The report discusses the efficacy of the safe leads, making recommendations for their improvement both in design and deployment.  In this regard Fishing Master Kazuhiro Yamazaki of the F/V Fukuseki No. 5 made important suggestions (principally using double weights) to allow the use of weighted branch lines without compromising crew safety from flying weights following "bite-offs", which are known sometimes to cause serious injuries. His ideas are planned to be tested in collaboration with Japan Tuna and Tuna South Africa in 2010.

 The final report of the research is expected early in 2010, in time to be tabled at the Fifth Meeting of ACAP's Advisory Committee, to be held in Argentina in April 2010.

 Reference

 Melvin, E., Guy, T. & Rose, B. 2009.  Branchline weighting on two Japanese joint venture vessels participating in the 2009 South Africa tuna fishery: a preliminary report. Seattle: Washington Sea Grant. 10 pp.  http://wsg.washington.edu/mas/resources/seabird.html.

 John Cooper, ACAP Information Officer, 15 November 2009, updated 19 November 2009