Blackwell Science, LtdOxford, UK FISFisheries Science0919-92682004 Blackwell Science Asia Pty Ltd 705October 2004 867 Migration of Euthynnus affinis near Taiwan W-D Chiou and L-K Lee 10.1111/j.1444-2906.2004.00867.x Original Article746757BEES SGML FISHERIES SCIENCE 2004; 70: 746–757 Migration of kawakawa Euthynnus affinis in the waters near Taiwan Wann-Duen CHIOU* AND Liang-Kang LEE Department of Fisheries, National Kaohsiung Marine University, Kaohsiung 811, Taiwan ABSTRACT: Kawakawa Euthynnus affinis is the most abundant species among the small tuna in the coastal waters of Taiwan. The migration pattern of kawakawa to Taiwan was determined in the present study based on the species’ feeding habits and reproductive biology and on temporal variation of catch for kawakawa and its prey fishes. Schools of this species successively migrate to Taiwan from September to May, and then move away in June. They travel to the waters off Taiwan with the warm Kuroshio current, migrate toward coastal waters for feeding and move away for spawning. It is suggested in the present study that the kawakawa spawning ground is in the waters of the northern Philippines. The migration of kawakawa exhibits size-segregating behavior. Schools of immature young fish first arrive in the coastal waters around Taiwan, followed by the adults. KEY WORDS: Euthynnus affinis, feeding ground, migration, Taiwan. INTRODUCTION migration in the Gulf of Oman and in Hong Kong,1,3 but the migration in the western Pacific Ocean has Kawakawa Euthynnus affinis is an epipelagic not yet been clarified. Although the food and feed- migratory tuna species that is widely distributed in ing habits,4 and the catch fluctuation in relation to the tropical and subtropical waters of the Indo– oceanographic and meteorological conditions of Pacific region. In the north-western Pacific Ocean, kawakawa have been documented,5 the reasons this species is distributed along the coastal area of why this species migrate to the coastal waters of the Asian continent from Malaysia north-eastward Taiwan have not been studied. Hence, the present through mainland China and Taiwan to southern study aimed to describe the seasonal pattern of Japan.1 Kawakawa is the dominant species among this species’ migration to the coastal waters of the small tuna caught in the coastal waters of Taiwan, and also to discuss the migration mecha- Taiwan, which include Katsuwonus pelamis, Auxis nism based on the species’ feeding habits and rochei and A. thazard. In recent years, the annual reproductive biology and on the temporal varia- production of kawakawa in the coastal waters of tion of catch for the prey fishes and kawakawa. Taiwan has been approximately 900 t – approxi- mately 43.3% of all small tuna. This species occurs primarily on the north-eastern, eastern and south- MATERIALS AND METHODS ern coasts of Taiwan and Penghu.2 Kawakawa are caught mainly by set net operating in coastal In order to elucidate the seasonal pattern of waters; however, small numbers of kawakawa are kawakawa migration to Taiwanese waters, com- also captured by gill net, long line and small purse mercial catch statistics were collected and ana- seine in eastern and south-western Taiwan. lyzed. These records included daily catch statistics The migration of kawakawa to the coast of of kawakawa from five set net sites along the coast Taiwan shows a seasonal pattern, which is well of Taiwan dating from 1980 to 2001, and those from reflected by the catches made by commercial fish- the offshore area of Taitung from 1994 to 2001. eries. Commercial catches of kawakawa are made Among these sites, the Pengshing and Mangfong mainly in spring and much less in summer. How- set net sites are located on the south-west coast ever, current knowledge of kawakawa migration is of Taiwan, and the Shinshyefa, Shinyahjou and limited. There are brief descriptions of kawakawa Sanyuhyih set net sites are located on the east coast of Taiwan (Fig. 1). The catch statistics of kawakawa *Corresponding author: Tel: 886-7-361-7141. from the Mangfong, Shinshyefa and Sanyuhyih set Fax: 886-7-364-4190. Email: [email protected] net sites were commercially categorized into three Received 11 June 2003. Accepted 19 April 2004. sizes according to fork length: small (<30 cm), Migration of Euthynnus affinis near Taiwan FISHERIES SCIENCE 747 Fig. 1 Map of Taiwan area showing the survey localities of kawakawa Euthynnus affinis catch data. medium (30–50 cm) and large (>50 cm). Those Fishermen’s Association were more detailed, they from the Pengshing and Shinyahjou set net sites were adopted to determine the months of the were categorized into two sizes: small (<50 cm) and kawakawa’s occurrence in offshore Taiwan. large (>50 cm). Normally, set net fishermen stop Fish samples were also collected for basic bio- any fishing activities in the typhoon season (July– logical study in an attempt to gain further insight September) to avoid damaging fishing gear. into the migration of kawakawa. In total, 966 However, the newly designed net at the Mangfong specimens, ranging from 253 to 681 mm fork net site enables the fishermen to operate all year length, were collected from 1995 to 2001. Some round. Kawakawa are mainly caught by drift gill net were obtained from Hwalien, eastern Taiwan, and and long line in eastern Taiwan and by small purse the rest were from Jwukeng and Linyuan, south- seine in south-western Taiwan all year round. western Taiwan. Fresh specimens were weighed to Because the catch records from the Taitung the nearest 1 g; fork length was measured to the 748 FISHERIES SCIENCE W-D Chiou and L-K Lee nearest 1 mm; and the gonads and stomach con- merase chain reaction (PCR) amplifications were tents were weighed to the nearest 0.01 g. The carried out, adopting the protocols of Innis et al.13 gonads and stomach contents were removed and A total of 35 cycles of 1.0 min at 94°C for denatur- preserved in 10% formalin for further treatment in ing, 1.0 min at 50°C for annealing and 1.5 min at the laboratory. The spawning season of kawakawa 72∞C for extension were carried out with a thermal was determined mainly by the gonadosomatic cycler (GeneAmp PCR System 9600, Perkin Elmer, index (GSI) in both sexes, and also by histological Norwalk, CT, USA). Two primers were used for the examination. The GSI was calculated as follows: PCR process; primer SP (5¢-TACCCCAAACTC- CCAAAGCTA-3 , modified from Rosel and Block),14 GSI (gonad weight/body weight) 103 (1) ¢ = ¥ which targets the light strand of the tRNAPro gene, Each food item in the stomach was identified to the and primer S12S (5¢-CAGAAGGCTAGGAC- lowest possible taxon and weighed to the nearest CAAACCT-3¢ modified from Kocher et al.),15 which 0.01 g, and the number of items was counted. The targets the heavy strand of the 12S-rRNA gene. species composition of food items was expressed Sequencing was performed with an ABI 377 auto- using the index of relative importance (IRI).6 This mated DNA sequencer (ABI, Foster City, CA, USA). index allowed the prey items to be ranked, and the For computing the genetic distances between relative importance of each food item was then pairs of populations, the pairwise FST values were compared among different localities.7 It was estimated using the method described by Tajima calculated by the following equation: and Nei,16 and the analysis of molecular variance (AMOVA) were analyzed for population subdivi- IRI (N% W%) F% (2) = + ¥ sion.17 The AMOVA analysis calculates genetic vari- where N% is the number of each food item as a ance components and hierarchical F-statistic percentage of the total number of all food items analogs (f-statistics), and tests the significance of identified; W% is the wet weight of each food item these observed variances using permutation as a percentage of the total wet weight of all food methods. In these f-statistics, fst is viewed as the items identified; and F% is the frequency of occur- correlation of random haplotypes within popula- rence of each food item as a percentage of the total tions, relative to that of random pairs of haplotypes number of stomachs containing any food. drawn from the whole species; fct as the correlation The control region is the most variable portion of random haplotypes within a group of popula- 8–10 of the mitochondrial DNA; therefore, a tions, relative to that of random pairs of haplotypes sequence analysis of this region is usually con- drawn from the whole species, and fsc as the ducted to analyze the stock structure.11 Fifty fish correlation of the molecular diversity of random samples were collected to identify the kawakawa haplotypes within populations, relative to that of stock. Among these samples, 42 individuals col- random pairs of haplotypes drawn from the region. lected from the coastal waters of south-western Both analyses were carried out using the program and north-eastern Taiwan in 2002 were assigned Arlequin.18 In the AMOVA analysis, individuals are to four spatio-temporal populations, and eight assigned to five populations based on geographic individuals collected from Laoag in the northern and temporal sampling, and these populations are Philippines in January 2003 were assigned to nested into groups. another population (Table 1). Approximately 2 cm3 of muscle tissue under the dorsal fin base was RESULTS removed from each individual and preserved in ethanol (95%) for further DNA experimentation in Temporal changes of catch the future. DNA was extracted from 50 individuals, fol- Monthly catches of kawakawa from various sites lowing the procedure of Hillis and Moritz with (Fig.