1. Vertical Distribution of Hairtail catch by vertical longline
Mun-Kwan Kim1, Su-Hyeon Park1, Tae-Cheol Oh1,
Hyeong-Cheol Kang1,Yong-Seok Park1,Young-il An2, Suk-Jong Kim3
1 Ocean and Fisheries Researches Institute, Jeju Special Self-Governing Provence
2Dept. of Maritime Police and Technology, Gangwon State University
3 Faculty of Ocean Science, Jeju National University
■ Introduction
To improve efficiency of hairtail trolling, it is important to understand the di stribution of hairtail based on diurnal migration in vertical level accurately. This study focused on the understanding of hairtail vertical distribution throu gh catching efficiency test by a vertical longline.
■ Material and Methods
. The efficiency test were carried out five times on the eastern coast of Jeju I sland from August to September in 2016: 11:00 AM to 03:00 PM in daytime, 11:00 PM to 03:00 AM in nighttime. A fishing gear was composed of twenty hooks per a set numbered in order from first hook near surface to the seabed of line. The depth of the first hook was 18 m, and last hook was 86 m, and p acific saury was used as baits. Ten sets of fishing gear per trip were used in t otal. After fishing, we counted hairtalis at each numbered hooks, which were summed up both by number and in aggregate.
Fig. 1. Schematic drawing of hairtail Vertical longline
Fig. 2. Vertical longline gear Fig. 3. Attached position of fathometer.
Fig. 4. Operation of hairtail vertical longline
■ Results and Discussion
a total of 232 hairtails were catched by 2,000 hooks: 193 individuals in day, 39 in night. The hook rate was 11.6%: 9.6% in day, 2.0% in night. In both da y and night times, there were variations in hook rates at each numbered hook . In daytime, a maximum of 28.5% at number 18, followed by 21.4% at 20, 10.7% at 17, which account for 60.6% of daytime hook rate while in nightti me, a maximum of 23.0% at 1, followed by 15.3% at 4 and 9, which account for 53.6% of nighttime hook rate. From the above result, hairtails usually dis tributed at deep region in daytime, whereas near the surface in nighttime. Th erefore, it is necessary to position trolling line within the distribution layer o f hairtail for the fishing efficiency .
Fig. 5. Frequency of fish caught for each hook(day)
Fig. 6. Frequency of fish caught for each hook(night)