Distribution of Seabird Bycatch at WCPFC and the Neighbouring Area of the Southern hemisphere
Incidental mortality of bycatch of seabirds, congregating around tuna longline fishery vessel and hooked branch lines seems one of the major risks for conservation of Procellariiforme species. Our study described distribution of the bycatch CPUEs of those species in the ocean of southern hemisphere, and examined their spatial and seasonal patterns. The distribution and the occurrence were compared with those in other area. Then, the area where mitigation measure should be introduced was discussed. Data from scientific observer programs, data from fishing boats for high school training and chartered research boats were used for the analyses. Bycatch CPUE (number of seabirds/ 1000 hooks) was calculated by species or species groups by 5x5 degree blocks, and its spatial distribution was presented. Operation data in the southern hemisphere were obtained mostly off South African water, off Chile water, southeast Indian Ocean and the Tasman Sea. By-catch CPUEs of seabirds were the highest in the Tasman Sea in WCPFC conventional area but the value was smaller than that in high interaction area out of the WCPFC area. In the southern WCPFC area, bycatch CPUE of albatrosses was observed more than that of petrels. Albatross species, mostly wandering albatrosses, black-browed albatrosses, Buller's albatrosses, and shy albatrosses, were caught in the Tasman Sea. On the other hand, white-chinned petrels and flesh-footed shearwaters, which are thought to dive deeper than albatrosses and by-caught frequently in the Atlantic and Indian Oceans, were not caught in the Tasman Sea. Albatrosses of higher conservational risks were exclusively caught in the area south of 25S, which indicates effective mitigation measures need to be introduced in the area. With the data from the WCPFC area, capture of white-chinned petrels did not statistically accounted for simultaneous capture of albatrosses and giant petrels in our data. A previous study showed that attack of white-chinned petrels against baited hooks lead bycatch of albatrosses in pelagic longline off south African water (Melvin et al. 2009), and relatively lower CPUEs of total albatrosses in the WCPFC area than the others could also be at least partially attributed to this fact. However, in the case of the Tasman Sea, albatrosses of higher conservation risks such as wandering albatrosses were by-caught without diving petrels. It is likely that the bycatch mechanism in the Tasman Sea differ from that off South Africa. To clarify the mechanism, more data and researches are needed in the Tasman Sea.