Shrink and defend: a comparison of two streamer line designs in the 2009 South Africa tuna fishery

Two types of streamer lines, a "light" with short streamers and a "hybrid" with mixed long and short streamers, were tested in the Japanese joint venture tuna fishery that operates in the South African EEZ.  The authors also looked at differences in catch rates between weighted and unweighted branchlines. The mean total attack rate was similar for each design but diving birds attacked further astern in response to both tori line types compared to surface foraging birds.  The "hybrid" line did not allow attacks by divers within 50 m but the "light" line allowed attacks through out all distances astern monitored. Surface foragers did not attack within 0-25 m of the "hybrid" line or at distances greater than 100 m of the "light" line.  Catch rates of birds were higher on unweighted compared to weighted branchlines.  Catch rates of fish were not significantly different between the two branchline types at night or during the dawn.