A comparison of two blue-dyed bait types for reducing incidental catch of seabirds in the experimental operations fo the Japanese Southern Bluefin Tuna Longline

The use of blue-dyed bait is one of the effective mitigation measures to reduce incidental catch of seabirds. However, the effect of the blue-dyed bait may be changed by bait types such as squid and fish. The effects of blue-dyed squid and fish baits for reducing incidental catch of seabirds were examined by the Japanese longline fishery survey cruises. The surveys were conducted by Matsuei-maru No.3 in 2001, Fukuseki-maru No.33 in 2002 and Fukuryu-maru No.21 in 2003 off South Africa in the Southern Ocean. Squid, sardine, striped mullet and mackerel were used as bait during the surveys. Results showed that the incidental catch of seabirds were lower for both blue-dyed squid and fish baits than that for non-dyed baits. A marked difference was recorded in the catch rate of seabirds by the Fukuseki-maru No.33, and no birds was taken by the Matsuei-maru No.3 and Fukuryu-maru No.21 when blue-dyed baits were used. Both blue-dyed squid and fish baits were effective in reducing the incidental catch of seabirds as compared with both non-dyed squid and fish baits.