Yeong Chull Park, Won Seok Yang and Tae Ik Kim
National Fisheries Research and Development Agency
Republic of Korea
ABSTRACT
This paper reviews the fluctuations in catch and fishing vessels, catch per unit effort (CPUE), fishing grounds, and length composition of the major species based on Korean commercial fishing data in the Pacific Ocean.
1. INTRODUCTION
The commercial fishing operations of the Korean longline fishery in the Pacific Ocean have been conducted for large-size yellowfin, bigeye, and albacore tunas since the mid-1960s. The Korean purse-seine fishery started experimentally in 1980 and commercial fishing activity began in the western tropical Pacific Ocean in 1982, targetting mostly skipjack tuna.
2. TRENDS IN FISHING VESSELS AND CATCHES
2.1 Longline Fishery
Nineteen fishing vessels operated in the Pacific Ocean in 1964. The fishing fleet gradually increased year by year to a peak of 270 vessels in 1974, then decreased to a low of 94 in 1985, and increased to 182 in 1990.
Catch of tuna and tuna-like species increased sharply from 2,400 mt in 1964 to 68,800 mt in 1976 with increasing number of vessels. After 1976 the catch declined to a lower level of 25,700 mt in 1984 along with a decrease in the number of vessels. However, it again showed an increasing pattern during the 1985–1990 period. About 44,800 mt of tunas were taken by 182 vessels in 1990 (Figure 1).
The catch of bigeye tuna was higher than that of either yellowfin or albacore during the 1975–1978 and 1987–1990 periods (Figure 2). The catch of yellowfin tuna was predominant during 1978–1980 and that of albacore during 1971–1973, 1981–1982, and 1985–1986. From 1983 to 1984, the catch of these three species showed lower levels than other years due to the decreased number of vessels. However, there seemed to be an increasing trend in catch of bigeye and yellowfin during the 1985–1990 period, except in 1988 and 1989. The catch of albacore showed a distinct decreasing trend from 1986 to 1990 because Korean tuna longliners changed their target species to yellowfin and bigeye tuna in recent years. In 1990, the catches of the major species were 20,800 mt of bigeye, 13,900 mt of yellowfin, and 3,200 mt of albacore.
Figure 1. Trend in total catch and fishing vessels for Korean tuna longline fishery in the Pacific Ocean, 1971–1990.
Figure 2. Trend in catch of yellowfin, bigeye, and albacore tuna by Korean tuna longline fishery in the Pacific Ocean, 1971–1990.
2.2 Purse-seine Fishery
Two Korean purse seiners caught 500 mt of tunas in the western tropical Pacific Ocean in 1980. The catch was under 15,000 mt between 1981 and 1985, but it increased considerably from 27,700 mt (13 vessels) in 1986 to 115,800 mt (30 vessels) in 1989. The catch of skipjack and yellowfin tuna also increased sharply from 9,700 mt to 80,900 mt and from 1,600 mt to 34,500 mt, respectively, during the 1985–1989 period. The catch composition was 75.0% skipjack, and 24,8% yellowfin during 1986–1989 (Figure 3 and 4).
Figure 3. Trend in total catch and fishing vessels for Korean tuna purse-seine fishery in the western Pacific Ocean, 1980–1989.
Figure 4 Trend in catch of tunas by Korean tuna purse-seine fishery in the western Pacific Ocean, 1980–1989.
3. TREND IN CPUE
3.1 Longline Fishery
Catch per unit effort (number of fish per 100 hooks) of yellowfin, bigeye, and albacore tuna taken by Korean longline fishery in the Pacific Ocean from 1975 to 1990 are shown in Figure 5.
The CPUE of yellowfin tuna fluctuated from 0.30 to 0.96 during 1975–1982 and it showed a more stable level of 0.46–0.64 during 1983–1990 period.
The CPUE of bigeye tuna remained at the level of 0.60 in 1975–1978 and decreased to the lowest level of 0.27 in 1981. However, it increased from 0.37 in 1982 to 0.68 in 1990.
The CPUE of albacore tuna increased from 0.20 in 1975 to the highest level of 1.35 in 1978, and thereafter fluctuated within the 0.65–0.99 range during the 1979–1986 period. From 1987, the CPUE decreased sharply to the lowest level in 1990.
Figure 5. Trend in catch per unit effort (no. fish per 100 hooks) of yellowfin, albacore and bigeye tuna by Korean tuna longline fishery in the Pacific Ocean, 1975–1990.
3.2 Purse-seine Fishery
The CPUE (mt per set) of skipjack and yellowfin tuna by the Korean purse-seine fishery in the western tropical Pacific Ocean from 1980 to 1989 are shown in Figure 6. The CPUE of skipjack reached a low level of 6.9 mt in 1981, and then it began an increasing trend up to 1989, except for 1984 and 1985. Skipjack tuna CPUE for 1988–1989 increased more than twice from that of 1984–1985. The CPUE of yellowfin tuna was much lower than that of skipjack. It also increased gradually during the 1981–1989 period.
Figure 6. Trend in catch per unit effort (mt per set) of tuna by Korean tuna purseseine fishery in the western Pacific Ocean, 1980–1989.
4. GEOGRAPHICAL DISTRIBUTION OF CPUE
4.1 Longline Fishery
The annual and seasonal geographical distributions of catch per unit effort (number of fish per 100 hooks) of yellowfin and bigeye tuna in the Pacific Ocean from 1988 through 1989 are shown in Figures 7 and 8. The major fishing grounds of yellowfin tuna were generally between 10°N and 15°S for the two years. The areas of high CPUEs were in the western central Pacific between 10°N to 10°S and 150°E to 155°W. From July to September the fishing grounds were more or less extended to the eastern Pacific, but the CPUEs were low.
The fishing grounds of bigeye tuna were mainly in the area between 15°N and 15°S during 1988 and 1989. The areas of high CPUEs were in the region of 15°N–15°S and 155° E–125°W in 1988. In 1989 the areas of high CPUEs were at 10°N–10°S, 160'E–160°W and at 10°N–10°S, 95°-115°W from April to December.
4.2 Purse-seine Fishery
The geographical distributions of CPUE (mt per set) of tunas taken by the Korean tuna purse-seine fishery in the western tropical Pacific Ocean from 1988 to 1989 are shown in Figure 9. The fishing grounds were formed in the area between 7°N–6°S and 140°-165°E. The areas of high CPUEs for skipjack tuna appeared to be uniformly distributed over the fishing grounds without any clear pattern, while high CPUEs for yellowfin appeared to be sparsely distributed.
Figure 7. Annual distribution of CPUE (no. fish per 100 hooks) for yellowfin and bigeye tuna by Korean tuna longline fishery in the Pacific Ocean, 1988–1989.
5. LENGTH COMPOSITION
5.1 Longline fishery
The fork-length composition of yellowfin and bigeye tuna taken by the Korean longline fishery in the Pacific Ocean from 1988 to 1989 are shown in Figure 10. The range and mean fork length of yellowfin tuna was 62–180 cm and 130.0 cm in 1988, and 70–185 cm and 129.5 cm in 1989, respectively. The length composition of yellowfin tuna for the two years was similar.
The range in fork length for bigeye tuna was 60–200 cm in 1988 and 1989, and the mean size was 132.4 cm in 1988 and 135.0 cm in 1989. The modal size of 1989 was larger than that of 1988.
5.2 Purse-seine Fishery
The fork-length composition of skipjack and yellowfin tuna taken by the Korean purse-seine fishery from 1988 to 1989 are shown in Figure 11. The range in fork length for skipjack was 30–78 cm in both years; the mean sizes were 53.4 cm in 1988 and 54.0 cm in 1989.
The range in fork length for yellowfin tuna was 40–170 cm for 1988 and 198; the mean size was 87.8 cm in 1988 and 88.5 cm in 1989. There seem to be three size groups in the length composition of yellowfin tuna during the two years. The modal lengths were 60–75 cm for small-sized fish, 110–115 cm for middle-sized fish, and 155–160 cm for large-sized fish.
Figure 8-1. Seasonal distribution of CPUE (no. fish per 100 hooks) for yellowfin tuna by Korean tuna longline fishery in the Pacific Ocean, 1988–1989.
Figure 8-2. Seasonal distribution of CPUE (no. fish per 100 hooks) for bigeye tuna by Korean tuna longline fishery in the Pacific Ocean, 1988–1989.
Figure 9. Annual distribution of CPUE (mt per set) for tunas by Korean tuna purseseine fishery in the western Pacific Ocean, 1988–1989.
Figure 10. Annual length composition of bigeye and yellowfin tuna taken by Korean tuna longline fishery in the Pacific Ocean, 1988–1989.
Figure 11. Annual length composition of skipjack and yellowfin tuna taken by Korean tuna purse-seine fishery in the western Pacific Ocean, 1988–1989.
