Korean tuna fisheries in the Pacific Ocean and interaction between the fisheries

Dae-Yeon Moon and Jung-No Kwon
National Fisheries Research and Development Agency
Sirang-ri, Kijang-up, Kyoungsangnam-do 626-900
Republic of Korea

ABSTRACT

This paper describes long-term trends of yellowfin CPUE estimated from Korean longline and purse seine catch of yellowfin tuna in the southwestern and central Pacific during 1982-93, together with recent Korean tuna fisheries in the Pacific Ocean. In the western tropical Pacific where operations of Korean longline and purse seine vessels overlapped, the yellowfin CPUE of Korean longliners remained relatively stable during a period when the purse seine catch rose dramatically from about 3,000 mt in 1986 to 67,000 mt in 1992. While these results suggest a lack of influence of purse seining on longline catches, it was noted that the impact of large catches of small yellowfin by the purse seine fishery may take time to show its effect on the yellowfin resource.

1. INTRODUCTION

The Korean distant water fishery began in 1957 in the Indian Ocean. Since then, Korean longline vessels have expanded operations into all of the world's oceans. For the Pacific tuna fishery which began some years later in mid-1960s, Korea had increased tuna longliners every year up to 270 vessels in 1974, followed by decrease in successive years to 94 vessels in 1985 and increased again thereafter (Gong et al., 1993). In addition to longliners, purse seiners started to operate exclusively in the southwestern Pacific since 1980. Compared to longliners, the size of the purse seine fleet is not large; during 1980-93 number of purse seiners averaged 20 each year.

The area that Korean tuna longliners and purse seiners operate overlap to some extent in the Pacific. This implies that certain types of interaction, as classified by Hampton (1994), between those two tuna fisheries on tuna species might occur. Tuna interaction studies certainly should be emphasized in order to promote effective management of tuna resources; however, these studies often require long-term efforts to secure sufficient information to analyse. In this sense, interaction studies for tuna species of world's oceans should be cooperative among tuna fishing countries for better results.

This paper describes long-term trends of yellowfin CPUE estimated from Korean longline and purse seine catch of yellowfin tuna in the southwestern and central Pacific during 1982-93, with a view to disclosing a possibility of interaction between the fisheries on yellowfin.

2. KOREAN TUNA FISHERIES IN THE PACIFIC

Catches by the Korean tuna vessels operating in the Pacific have increased year by year and exceeded 100,000 mt for the first time in 1987 (Park et al., 1990). The 1987 tuna fleet consisted of 138 longliners and 20 purse seiners. During 1990-92, the catch by the Korean tuna fleet amounted to over 200,000 mt annually (Tables 1 and 2); however, in 1993 the catch decreased significantly to about 160,000 mt. This decrease was largely attributed to the decrease in catch by purse seiners (Table 2) rather than the decrease in catch by longliners of relatively small fleet size compared to previous year. Currently about 150 longliners and 30 purse seiners are engaged in tuna fishing in the Pacific.

2.1 Longline Fishery

The number of Korean longliners operating in the Pacific ranged from 100 to 200 vessels during 1980s and up to the present (Park et al., 1990; Gong et al., 1993); the catch by the longline fleet also varied by year but did not correspond closely with the changes in effort. During 1990-93, the average number of longliners and catch were 179 vessels and 40,000 mt, respectively (Table 1). During this period the catch and number of vessels showed a decreasing trend.

Species composition of longline catch was 50% bigeye, 29% yellowfin and 21% other species, on average (Table 3). The CPUE of all species by longliners ranged from 1.3 to 1.8 fish/100 hooks during 1990-93; the CPUE decreased in 1993 by 19% compared to 1992 (Table 1). In recent years, fishing grounds for the longline fishery have become narrower by giving up albacore catch from the southern and northernmost part of Korea's usual fishing grounds in the Pacific (Figure 1). Fishing activities have been generally concentrated in the southwestern and central Pacific since 1989 (Gong et al., 1993).

2.2 Purse Seine Fishery

The Korean purse seine tuna fishery which targets mainly skipjack and yellowfin tunas recorded the highest total catch at 227,518 mt with 36 vessels in 1991, but showed decreasing trends thereafter (Table 2). Species composition of purse seine catch was 69% skipjack and 31% yellowfin tuna on average (Table 3). The CPUE for all species by purse seine fluctuated between 20 and 27 mt/haul in recent years; CPUE of yellowfin remained similar level for each year, whereas that of skipjack decreased from 20 mt/haul in 1991 to 13 mt/haul in 1993.

Fishing area by purse seine extended westward in recent years compared to late 1980s (Figure 2). In the late 1980s the range of purse seine fishing operation was between 138-166ºE, while in 1990-93 it was between 135ºE-175ºW.

Table 1. Number of vessels, catch, and CPUE of Korean longline fishery in the Pacific Ocean during 1990-93.

Year	Vessels	Catch (mt)	CPUE (no. fish/100 hooks)
			All	YFT	BET	ALB	OTH
1990	182	44,762	1.40	0.55	0.69	0.07	0.09
1991	220	38,751	1.32	0.40	0.71	0.11	0.10
1992	166	40,756	1.75	0.66	0.74	0.18	0.17
1993	148	36,459	1.41	0.48	0.67	0.09	0.17

All: all species, YFT: yellowfin, BET: bigeye, ALB: albacore, OTH: others

Year	Vessels	Catch (mt)	CPUE (mt/haul)
			All	YFT	SKJ	OTH
1990	39	173,343	41.4	9.0	32.1	0.3
1991	36	227,518	27.4	7.5	19.8	0.1
1992	36	182,287	24.3	8.6	15.7	-
1993	34	126,648	20.4	7.8	12.6	-

All: all species, YFT: yellowfin, SKJ: skipjack, OTH: others

Year	Longline Catch (%)			Purse Seine Catch (%)
	BET	YFT	OTH	SKJ	YFT	OTH
1990	46.5	31.0	22.5	80.0	20.0	-
1991	52.5	27.5	20.0	75.6	24.4	-
1992	48.5	30.7	20.8	63.2	36.8	-
1993	54.5	27.4	18.1	58.4	41.6	-

BET: bigeye, YFT: yellowfin, SKJ: skipjack, OTH: others

Among the interaction types classified by Hampton (1994), the interaction between two different fishing gears on certain tuna species can be studied when catch and CPUE data are available. Tuna fisheries interaction study, therefore, may not obtain anticipated results without such sufficient information from each fishery involved.

Figure 1. Korean longline fishery operation area and CPUE distribution of all species, 1990-93.

Figure 2. Korean purse seine fishery operation area and CPUE distribution of all species, 1990-93.

For interaction study, we reviewed changes in yellowfin CPUE by Korean longliners to see if it was affected by yellowfin catch by Korean purse seiners operated in the same area and same time. The shaded rectangle shown in Figure 3 between 140-180ºE and between 10ºN-10ºS represents an area in which interactions between Korean longline and purse seine fisheries on yellowfin might have occurred.

Figure 3. Interaction zone.

Yellowfin CPUE from longline fishery in this interaction zone during 1982-93 varies by year, ranging from 0.61 to 1.46, but as year progresses it becomes relatively stable (Figure 4). Even though wide range of changes was shown, yellowfin CPUE by Korean longliners in recent years appeared to be similar to that at the early phase of Korean purse seine fishery. The CPUE during the 1982-86 period when the purse seine catch amounted to nearly 1,000 to 3,000 mt was 0.92/100 hooks on an average, and that during 1987-93 when the purse seine catch increased dramatically up to about 67,000 mt was 0.91/100 hooks.

From these results, it was noted that there was no direct interaction between the purse seine catch and longline catch rates in the southwest Pacific and these results were consistent with those taken by Suzuki (1988). However, considering the purse seine catches are usually made of much smaller yellowfin, which will grow to be part of longline catches after some years depending on oceanographic conditions, the impact of large catches of small yellowfin by the purse seine fishery may take time to show its effect on the yellowfin resource (Hampton, 1994; Medley, 1994).

Figure 4. Changes in yellowfin tuna catch by purse seiners (open) and CPUE by longliners (closed) during 1982-93.

4. REFERENCES CITED

Gong, Y., J.U. Lee, Y.C. Park, D.Y. Moon, W.S. Yang, T.I. Kim, J.N. Kwon, J.B. Kim, H.S. Jo and Y.J. Lee. 1993. Fishery Statistics and fishing grounds for the Korean tuna longline fishery, 1988-1992. Tech. Rep. Nat. Fish. Res. Dev. Agency 106: 465 p.

Hampton, J. 1994. A review of tuna fishery interaction issues in the western and central Pacific Ocean. In: Shomura, R.S., J. Majkowski and S. Langi (eds.). Interactions of Pacific tuna fisheries. Proceedings of the First FAO Expert Consultation on Interactions of Pacific Tuna Fisheries, 3-11 December 1991, Noumea, New Caledonia. Vol. 1: Summary report and papers on interaction. FAO Fish. Tech. Pap. (336/1): 138-157.

Medley, P.A.H. 1994. Estimating the impact of purse-seine catches on longline. In: Shomura, R.S., J. Majkowski and S. Langi (eds.). Interactions of Pacific tuna fisheries. Proceedings of the First FAO Expert Consultation on Interactions of Pacific Tuna Fisheries, 3-11 December 1991, Noumea, New Caledonia. Vol. 1: Summary report and papers on interaction. FAO Fish. Tech. Pap. (336/1): 182-198.

Park, J.S., Y. Gong, Y.C. Park, W.S. Yang, T.I. Kim and Y.J. Lee. 1990. Annual report of catch and effort statistics and fishing grounds for the Korean tuna longline fishery, 1986-1987. Fish. Res. Dev. Agency. 447 p.

Suzuki, Z. 1988. Study of interaction between longline and purse seine fisheries on yellowfin tuna, Thunnus albacares (Bonnaterre). Bull. Far Seas Fish. Res. Lab. 25: 73-136.