CATCH CHARACTERISTICS OF TROPICAL TUNA CAUGHT BY KOREAN TUNA LONGLINE FISHERY IN THE ATLANTIC OCEAN

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1 SCRS/13/6 Collect. Vol. Sci. Pap. ICCAT, 7(6): (1) CATCH CHARACTERISTICS OF TROPICAL TUNA CAUGHT BY KOREAN TUNA LONGLINE FISHERY IN THE ATLANTIC OCEAN Sang Chul Yoon 1, Zang Geun Kim, Sung Il Lee, Heewon Park, Dong Woo Lee SUMMARY The average of total catch by Korean tuna longline fishery in the Atlantic Ocean was about 3, mt from 1986 to 11. Average catch proportion by species caught from 1986 to 11 was 9.8% for bigeye tuna, 1.1% for yellowfin tuna. The average catch of bigeye tuna was about 1,8 mt and CPUE had recorded the highest at 9.1 inds./1, hooks in 7. The average length distribution of bigeye tuna was 13.1cm, 13.9cm and 1.3cm in 9, and 11. The average catch of yellowfin tuna was about 59 mt and CPUE recorded the highest at.3 inds./1, hooks in. The average length distribution of yellowfin tuna was 139.5cm, 131.1cm and 133.5cm in 9, and 11. The fishing ground for bigeye tuna and yellowfin tuna was mainly formed from the north of N to the south of 1S from 7 to 8. In this study, we would like to introduce the catch characteristics of tropical tuna caught by Korean longline fishery in Atlantic Ocean, and these results will be used as fundamental data for fisheries management and stock assessment. RÉSUMÉ Entre 1986 et 11, la prise moyenne totale de la pêcherie palangrière coréenne de thonidés opérant dans l'océan Atlantique s'est élevée à environ 3. t. La proportion moyenne des captures par espèce capturée entre 1986 et 11 s'établissait à 9,8% pour le thon obèse et 1,1% pour l'albacore. La prise moyenne de thon obèse se chiffrait à environ 1.8 t et la CPUE a atteint son point culminant à 9,1 spécimens/1. hameçons en 7. La distribution des tailles moyennes du thon obèse s'est établie à 13,1 cm, 13,9 cm et 1,3 cm en 9, et 11. La prise moyenne d'albacore se chiffrait à environ 59 t et la CPUE a atteint son point culminant à,3 spécimens/1. hameçons en. La distribution des tailles moyennes de l'albacore s'est établie à 139,5cm, 131,1cm et 133,5cm en 9, et 11. La zone de pêche du thon obèse et de l'albacore s'étendait essentiellement du Nord de ºN au Sud de 1ºS de 7 à 8. Dans cette étude, nous souhaitons présenter les caractéristiques de la prise des thonidés tropicaux capturés par la pêcherie palangrière coréenne opérant dans l'océan Atlantique, et ces résultats seront utilisés comme données de base pour la gestion des pêcheries et l'évaluation des stocks. RESUMEN La media de la captura total de la pesquería de palangre dirigida a los túnidos de Corea en el océano Atlántico fue de aproximadamente 3. t desde 1986 a 11. La proporción de captura media por especies capturadas desde 1986 a 11 fue de 9,8% para el patudo y 1,1% para el rabil. La captura media de patudo fue de alrededor de 1.8 t y la CPUE alcanzó el mayor valor en 9,1 ejemp./1. anzuelos en 7. La distribución media de tallas de patudo fue de 13,1 cm, 13,9 cm y 1,3 cm en 9, y 11. La captura media de rabil fue de alrededor de 59 t y la CPUE alcanzó el mayor valor en,3 ejemp./1. anzuelos en. La distribución media de tallas de patudo fue de 139,5 cm, 131,1cm y 133,5 cm en 9, y 11. El caladero de patudo y de rabil ocupaba principalmente el área desde el norte de ºN hasta el sur de 1º S desde 7 a 8. En este estudio, deseamos introducir las características de la captura de los túnidos tropicales capturados por la pesquería de palangre de Corea en el océano Atlántico y estos resultados se utilizarán como datos fundamentales para la ordenación pesquera y la evaluación de stock. 1 National Fisheries Research and Development Institute (NFRDI), Busan, Korea, ( scyoon@korea.kr) 595

2 KEYWORDS Korean tuna longline, Catch, CPUE, Distribution, Range of length 1 Introduction Korean distant water tuna longline fishery commenced in 1957 in the Indian Ocean and expanded to the Pacific Ocean in 1958 and the Atlantic Ocean in early 196s. Since then, it has become one of the most important fisheries in Korea together with the domestic fisheries. In Atlantic Ocean, number of active longline fishing vessels showed a decreasing tendency overall, the number of longline fishing vessels had increased to in 8. In recent years, number of longline fishing vessels was 16 in Atlantic Ocean in 11. The major species were bigeye tuna, yellowfin tuna, and albacore tuna (Table 1). In this study, we would like to introduce the catch characteristics of tropical tuna species caught by Korean longline fishery in the Atlantic Ocean using the catch data and fishery information compiled from logbook, distribution of its fishing ground and length distribution, and to give the information being useful for stock assessment of this species. Data and Methods The nominal catch data by species for Korean tuna longline fishery in the Atlantic Ocean (KOFA, ) were used to investigate catch characteristics of major tunas caught by Korean tuna longline fishery in the Atlantic Ocean. Catch per unit effort (CPUE) of major tunas caught by Korean longline fishery was estimated using catch by species and effort (number of hooks) data aggregating from logbook by year, and its distribution of fishing grounds was indicated. Length frequency of major tunas was analyzed using observer data and fisherman data measured onboard. 3 Results 3.1 Catch of Korean tuna longline fishery The average of total catch by Korean tuna longline fishery in the Atlantic Ocean was about 3, mt from 1986 to 11. The catch recorded the highest at 13, mt in 1989, and then it had decreased to the lowest at 97 mt in and then it had been increased, it showed around,6 mt in 11. In recent years, it had shown an increasing trend. CPUE of Korean tuna longline fishery in the Atlantic Ocean had started to increase since 1, and recorded the highest at 13.8inds./1, hooks in 5. After then, it has shown a decreasing trend (Figure 1). Average catch proportion by species caught by Korean tuna longline fishery in the Atlantic Ocean from 1986 to 11 was 9.8% for bigeye tuna which was the highest, 1.1% for yellowfin tuna, 6.1% for bluefin tuna and 5.3% for southern bluefin tuna and 3.% for albacore tuna. Catch proportion by species was 59.9% for bigeye tuna which was the highest, 1.6% for yellowfin tuna,.8% for albacore tuna in 11 (Figure ). Figure 3 shows the spatial distribution of fishing ground of Korean tuna longline fishery in the Atlantic Ocean. The fishing ground was formed mainly from the north of N to the south of 1S from 7 to 8. And it expanded to the south of 5S in 9 and Catch characteristics of tropical tuna caught by Korean tuna longline fishery 3..1 Bigeye tuna The average of bigeye tuna catch by Korean tuna longline fishery in the Atlantic Ocean was about 1,8 mt from 1986 to 11. The catch recorded the highest at 7,9 t in 1989, and then it had decreased to the lowest at 1 mt in 1 and then it had been increased, it showed around,7 t in 11.CPUE of bigeye tuna in the Atlantic Ocean had started to increase since 1, and recorded the highest at 9.1inds./1, hooks in 7. After then, it has shown a decreasing trend (Figure. ). Figure 5 shows the recent monthly average catches of bigeye tuna caught by Korean tuna longline fishery in the Atlantic Ocean. It shows the lowest level of 1 t in July and the highest level of 9 t in January. 596

3 Figure 6 shows the spatial distribution of fishing ground of bigeye tuna caught by Korean tuna longline fishery in the Atlantic Ocean. The fishing ground for bigeye tuna was formed mainly from the north of N to the south of 1S from 7 to 8. And it expanded to the south of 5S in 9. Formation pattern of fishing ground was similar with spatial distribution of Korean tuna longline fishery in the Atlantic Ocean. The length distribution of bigeye tuna caught by Korean tuna longline fishery in the Atlantic Ocean was shown that the range of length was 95-5cm (mean 13.1cm) in 9,71-cm (mean 13.9cm) in, 63-87cm (mean 1.3cm) in 11, respectively. The main mode of length was 117cm of 9, 135cm of, and 119cm of 11 (Figure 7). 3.. Yellowfin tuna The average of yellowfin tuna catch by Korean tuna longline fishery in the Atlantic Ocean was about 59mt from 1986 to 11. The catch recorded the highest at,5 mt in 1989, and then it had decreased to the lowest at 3mt in 1 and then it had been increased, it showed around 9mt in 11. CPUE of yellowfin tuna in the Atlantic Ocean recorded the highest at.3inds./1, hooks in. After then, it has shown a decreasing trend (Figure 8). Figure 9 shows the recent monthly average catches of yellowfin tuna caught by Korean tuna longline fishery in the Atlantic Ocean. It shows the lowest level of 9 t in April and the highest level of 68 t in February. Since May, monthly average catches did not show large fluctuation. Figure 1 shows the spatial distribution of fishing ground of yellowfin tuna caught by Korean tuna longline fishery in the Atlantic Ocean. The fishing ground for yellowfin tuna was formed mainly from the north of N to the south of 1S from 7 to 8. And it expanded to the south of 5S in 9. Formation pattern of fishing ground was similar with spatial distribution of Korean tuna longline fishery in the Atlantic Ocean. The length distribution of yellowfin tuna caught by Korean tuna longline fishery in the Atlantic Ocean was shown that the range of length was cm (mean 139.5cm) in 9, 93-17cm (mean 131.1cm) in, cm (mean 133.5cm) in 11, respectively. The main mode of length was 13 cm and 15cm of 9, 115cm of, and there were 3 modes of length was18cm, 15cm and 163cm of 11, respectively (Figure 11). References KOFA (Korea Overseas Fisheries Association) Statistical year book of overseas. 39pp. 597

4 Table 1. Nominal catch (t) of tropical tuna caught by Korean longline in the Atlantic Ocean, Year No. of vessels BFT YFT ALB BET SBF SKJ OTH Total , ,8-11 1,89 9, ,57 1,38-6 1,83 7, , , ,5 7, , ,896-6,75 13, , , , , , , ,5 - -, , , , , , , , , , , , , , ,76 7-1,,61 598

5 Catch proportion (%) Catch (mt) CPUE (inds./1, hooks) 1, 1, 1, 8, 6,,, Year Catch CPUE Figure 1.Variations in catches and CPUE of Korean tuna longline fishery in the Atlantic Ocean from1986 to 11. 1% 8% 6% % % % Year ALB BET BFT SBF SKJ YFT OTH Figure.Catch proportion by species caught by Korean tuna longline fishery in the Atlantic Ocean from 1986 to

6 8N 7 8N < < 1W 8 E 1W 8 E 8N 9 8N < < 1W 8 E 1W 8 E 8N < 1W 8 E Figure 3. The spatial distributions of catch for Korean tuna longline fishery in the Atlantic Ocean for 5 recent years (7-11). 6

7 Catch (mt) Catch (mt) CPUE (inds./1, hooks) 1, 8, 1 8 6,,, - 6 Catch CPUE Figure. Variations in catches and CPUE of bigeye tuna caught by Korean tuna longline fishery in the Atlantic Ocean from 1986 to Month Figure 5. Monthly average catches of bigeye tuna caught by Korean tuna longline fishery in the Atlantic Ocean from 7 to

8 8N 7 8N z 1W 8 E 1W 8 E 8N 9 8N 5-1z 5-1z 1W 8 E 1W 8 E 8N z 1W 8 E Figure 6. The spatial distributions of catch for bigeye tuna caught by Korean tuna longline fishery in the Atlantic Ocean for 5 recent years (7-11). 6

9 Catch (mt) Catch (mt) CPUE (inds./1, hooks) N = 3 X = 13.1 cm 3 N = 76 X = 13.9 cm N = 1685 X = 1.3 cm 1 Figure 7. The length distribution of bigeye tuna caught by Korean tuna longline fishery in the Atlantic Ocean from 9 to 11. 3,,5, 1,5 1, 5-6 Catch CPUE Figure 8. Variations in catches and CPUE of yellowfin tuna caught by Korean tuna longline fishery in the Atlantic Ocean from 1986 to Month Figure 9. Monthly average catches of yellowfin tuna caught by Korean tuna longline fishery in the Atlantic Ocean from 7 to

10 8N 7 8N W 8 E 1W 8 E 8N 9 8N W 8 E 1W 8 E 8N W 8 E Figure 1. The spatial distributions of catch for yellowfin tuna caught by Korean tuna longline fishery in the Atlantic Ocean for 5 recent years (7-11). 6

11 N = 1 X = cm N = 131 X = cm 3 11 N = 19 X = cm 1 Figure 11. The length distribution of yellowfin tuna caught by Korean tuna longline fishery in the Atlantic Ocean from 9 to