Comparison of circle hook and J hook catch rate for target and bycatch species taken in the Korean tuna longline fishery during 2005–2006
The National Fisheries Research And Development Institute (NFRDI), Republic Of Korea conducted a circle hook experiment to compare the catch rates of target and bycatch species between J hook and circle hooks in the tuna longline fishery of the eastern Pacific Ocean between 9 13'S~1 36'N and 126 00' ~138 21'W from September 20 to October 23, 2006. For this experiment, two scientists were deployed on one Korean longliner (416 GRT) in the eastern Pacific fishery targeting tuna and billfishes. Four types of hooks were used, size 4.0 traditional tuna hooks (J4), size 15 circle hooks (C15), size 16 circle hooks (C16) and size 18 circle hooks (C18). In the target species group, no significant differences among the 4 types of hook were revealed. In the bycatch species group, significant differences were found among the 4 types and between J-4 and each of the circle hooks. But there were no significant differences among the circle hooks.
For the tunas group, J4 hooks had a lower catch rate than those of the 3 types of circle hooks, while for the billfishes group the catch rate of J4 hooks was higher than those of the 3 types of circle hooks. For the sharks group, the catch rate of J4 hooks was much higher than those of the circle hooks. These results were very different from the results of the 2005 research survey, which was revealed that the catch rate of C18 for target species, tuna and billfishes, was much lower that of the other hooks, J4 and C15. Squid and jack mackerel baits had a high catch rate for the tuna group and other fishes group, as did chub mackerel bait for the billfishes and sharks group. Milkfish bait had low catch rate for all groups except the tuna group. The length frequency of bigeye tuna by hook type showed very similar distribution; slight differences were found between hook types in the bycatch species.
NFRDI conducted the circle hook experiment in 2005 and 2006 but there are differences in results between the two. The efficiency of catch rate by hook type and size is not clear. Consequently, similar research will again be conducted in the western central Pacific Ocean in 2007.