A REVIEW OF THE BIOLOGY AND FISHERIES FOR KAWAKAWA (EUTHYNNUS AFFINIS) IN THE INDO-PACIFIC REGION

Mitsuo Yesaki
Indo-Pacific Tuna Development and Management Programme
Colombo, Sri Lanka

1. INTRODUCTION

A synopsis of the genus Euthynnus was completed by Yoshida (1979) and a synopsis of kawakawa (E. affinis) was compiled by Yesaki (1989a). This review was abridged from the synopsis by the latter author. Some new information available since publication of this synopsis have been incorporated in this review.

2. CLASSIFICATION

Phylum Chordata
    Subphylum Vertebrata
        Superclass Gnathostomata
            Class Osteichthyes
                Subclass Actinopterygii
                    Order Perciformes
                        Suborder Scomberoidei
                            Family Scombridae
                                Subfamily Scombrinae
                                    Tribe Thunnini
                                        Genus Euthynnus
                                            Species affinis

3. EARLY LIFE HISTORY

Buñag (1956) and Rao (1964) described the development of ovarian ova of kawakawa, and Kaya et al. (1981) described the development of ova during the first artificially-induced spawning experiments with this species. The first cleavage divisions were observed at about 1 h after fertilization and the first hatching at about 31 h in temperatures that ranged between 21° and 26°C. The yolk sac was absorbed over 2 days.

The larvae of kawakawa have been described in detail by Matsumoto (1958) and the juveniles by Wade (1950a) and Jones (1960).

Kawakawa larvae appear to be very patchy and are widely distributed and generally taken close to land masses (Matsumoto, 1958; Nishikawa et al., 1985). Nishikawa et al. (1985) shows the highest concentrations of Euthynnus from the central and western Pacific off northwestern Australia, Java, and Papua New Guinea and off the Ryukyu and Solomon Islands.

Two kawakawa larvae were captured in plankton tows at a diel variability station about 15 miles southwest of the island of Hua Pou in the Marquesas Islands (Nakamura and Matsumoto, 1967).

A small-mesh mid-water trawl was fished 83 times at various locations around Hawaii to capture juvenile tunas (Higgins, 1970). Kawakawa were captured only off Oahu during these explorations. Of the 25 juveniles captured, 23 were captured in the inshore areas (7–9 km from land), whereas, only two were captured in the offshore area (56 km from land). The catches per tow averaged 0.1, 0.1, and 2.5 larvae during July, August, and September, respectively, in the inshore area.

Chamchang and Chayakul (1988) studied the distribution and abundance of small tuna larvae in the western Gulf of Thailand. Kawakawa larvae were the least abundant of the three kinds of tuna larvae captured in this area and were captured only in April and June.

Kawakawa larvae accounted for 24 percent of all tuna larvae (146 specimens) captured during a survey of the Ragay Gulf, Burias Pass, and Ticao Pass region of the Philippines (Abuso, 1988). These kawakawa larvae were captured in temperatures and salinities ranging from 24.7° to 28.9°C and 33.53°/.. to 34.66°/.., respectively.

Juvenile kawakawa are commonly captured in fisheries of many countries. Yabe et al. (1953) found juvenile kawakawa ranging in size from 18.3 to 33.2 cm during August to October among fish caught in Aburatsu, Japan. Jones (1960) described juveniles of kawakawa (2.5 to 22.2 cm) captured by beach seines off the southwest coast and by boat seines off the south coast of India. Siraimeetan (1985) collected 106 specimens ranging in size from 6.2 to 19.8 cm from the sardine-gillnet fishery off Tuticorin, India, during June-September. Wade (1950a) obtained many of his juvenile and preadult kawakawa from various fish markets in the Philippines. Juvenile kawakawa ranging in size from 16 to 32 cm make up the bulk of the catch by the troll-line fishery in Sri Lanka (Sivasubramaniam (1970). A high percentage of the kawakawa captured by Thai purse seiners in the Gulf of Thailand is comprised of fish in the 12- to 32-cm interval (IPTP data files). The frequent capture of kawakawa juveniles is attributed to the neritic habit of the species.

4. AGE AND GROWTH

Numerous studies have been completed to determine the age and growth of kawakawa. These include 13 studies based on length-frequency distributions and one study each on vertebrae, dorsal spines, and otoliths (Table 1).

Available evidence suggests rapid growth during the juvenile stage of kawakawa. Yabe et al. (1953) sampled juvenile kawakawa landed at Aburatsu, Japan, during August-October 1950 (Figure 1). The mean size of the juveniles increased from 20.0 to 27.2 cm in 53 days.

Kawakawa ranging from 12 to 57 cm are captured in the purse-seine fisheries of the Gulf of Thailand. Length-frequency distributions of juveniles (12–30 cm) captured during August-December 1987 were examined by Yesaki (1989b). Frequency distributions were grouped by 5-day intervals to show entry and progression of cohorts. Six cohorts were identified in the 15- to 25-cm interval. Modal progressions of these cohorts ranged from 4.80 to 7.20 cm per month, and averaged 5.76 cm per month (Figure 2).

Table 1. Summary of age and growth studies on kawakawa by length-frequency distributions and hard parts (from Yesaki, 1989b).

¹ - median

Figure 1. Mean lengths of juvenile kawakawa captured off Aburatsu, Japan during August-October (data from Yabe, 1953).

The initial length-based studies, including those of Ommanney (cited in Yoshida, 1979), Williamson (1970), and Chiampreecha (1978), subjectively assigned ages to prominent modal lengths. In later studies, Klinmuang (1978), Yesaki (1982; 1989b), and Supongpan and Saikliang (1987) estimated growth by “pen and paper” tracing of modal progressions. More recently, Silas et al. (1985b) and Joseph et al. (1987) used computer programmes to derive growth parameters and relative ages. The results for seven of the 11 length-based studies are very similar (Figure 3). Lengths at age derived from these seven studies range from 25 to 33, 43 to 51, and 52 to 65 cm for ages 1, 2, and 3, respectively.

Landau (1965) and Shabotinets (1968) determined age of kawakawa by counting annuli on vertebrae and dorsal spines, respectively. Their results are similar to the majority of the length-based estimates with lengths of 35, 46, and 51–58 cm for ages 1, 2, and 3, respectively (Figure 3).

Uchiyama (1980) examined the microstructure of otoliths for age and growth of kawakawa in the 20- to 70-cm range. Increment counts were validated as daily events in this study by either injecting or feeding fish with oxytetracycline; these fish were maintained at the Kewalo Research Facility of the National Marine Fisheries Service, Honolulu Laboratory. Uchiyama (1980) obtained lengths of 41 cm for age 1, and 68 cm for age 2. Yesak (1989b) obtained lengths of 47 and 65 cm for these respective ages by following modal progressions by the “pen and paper” method in frequency distributions grouped by 10-day intervals (Figure 3).

Figure 2. Modal progressions of juvenile kawakawa captured by the purse-seine fishery of the Gulf of Thailand (from Yesaki, 1989).

Age and growth studies of kawakawa completed to date give conflicting results. Length-frequency distributions of juveniles show rapid growth during early life. Also, otolith-increment counts of adults give length-at-age 1 of about 41 cm and length distributions grouped by 10-day intervals give 47 cm at age 1. Conversely, length distributions of adults grouped by monthly intervals give length-at-age 1 of between 25 and 33 cm.

Figure 3. Estimates of growth and relative age (yr) for kawakawa from length-frequency analyses (crosses: manual method; triangles: computer programmes) and hard parts (squares) (from Yesaki, 1989).

5. MATURATION, SPAWNING, AND SEX RATIO

5.1 Maturation

Tunas captured principally by trolling during exploratory fishing activities in the Philippines were examined for maturity (Wade, 1950b). The smallest ripe, spawning, and spent female kawakawa found during this survey were 40, 45, and 40 cm, respectively.

Buñag (1956) measured ova diameters of 30 fish to determine maturity of kawakawa captured in the Philippines, and correlated the development of ova to the various maturity stages. The smallest mature and spent females examined were 49.0 cm and 47.7 cm, respectively. A larger sample of 144 kawakawa, ranging in length from 33.1 to 65.2 cm, was examined by Ronquillo (1963) in the Philippines. He observed gonad indices greater than 3.0 (mature) in females ranging from 38.5 to 65.0 cm. Klinmuang (1978) suggested that kawakawa from the Gulf of Thailand and east coast of Peninsular Malaysia attained sexual maturity at between 37 and 42 cm. A total of 1,010 specimens from the Gulf of Thailand was examined over a 4-year period by Cheunpan (1984). She found the smallest mature female at 33.4 cm and 50 percent of the females to be mature at approximately 40.0 cm. Off the west coast of Thailand, a sample of 222 maturing (stage-III) females showed the smallest to be 38 cm and 93 percent to be 43 cm and larger (Yesaki, 1982).

Muthiah (1985) examined 198 females and 183 males captured off Mangalore, India, and found the size of 50-percent maturity was 43 cm and 44 cm, respectively, though males less than 43 cm were not examined.

These studies indicate that kawakawa attains maturity at about 38 cm. Kawakawa in Papua New Guinea may mature at a larger size, as the smallest fish with maturing oocytes was 48.9 cm fork length (Wilson, 1981).

5.2 Spawning

Kawakawa are suspected to spawn near the coast on the east side of Hong Kong. The spawning in this area takes place during June-August (Williamson, 1970).

Six ripe kawakawa were found off Vizhingam, India, two in May and four in August. Rao (1964) gives the spawning season as April to September, but does not discount spawning during other months. On the other hand, Muthiah (1985) gives the spawning season off Mangalore, India, as extending from October to May. He speculated that kawakawa enters inshore waters for spawning because of the high incidence of ripe fish in gillnet catches during October of each year.

Kawakawa in all stages of maturity were captured during most months in the Philippines. Therefore, Wade (1950b) concluded that spawning occurred throughout the year. A total of 110 spawning and/or spent females were found in January-July and October-November. The highest gonad index for kawakawa in the Philippines occurred in March (Ronquillo, 1963).

The highest percentage of maturing (stage-III) females was observed during September-April off the west coast of Thailand (Yesaki, 1982). Mature 9 (stage-IV) kawakawa were found in March and September and a spent (stage-V) female in February. Two spawning seasons were indicated by maturity stages; the principal season from February to April and the second season in September. Gonad indices for kawakawa in the Gulf of Thailand were consistently higher during April-July and December-January (Cheunpan, 1984).

These studies indicate that there are two spawning seasons for kawakawa in the equatorial regions. In the northern hemisphere, the principal spawning season generally occurs during the first half of the year and the secondary spawning season during the latter half. At higher latitudes of the tropical zone, there appears to be only one spawning season near the middle of the year.

Few studies have been published on the fecundity of kawakawa. Rao (1964) counted the number of opaque maturing ova and ripe translucent ova in ripe gonads of five kawakawa captured off Vizhingam, India. Counts of all ova and of ripe ova were used to estimate numbers released during the spawning season during each spawning, respectively. The numbers estimated to be released during each spawning ranged from 210,000 to 680,000 ova and during the spawning season from 790,000 to 2,500,000 ova. These fish ranged in size from 48.0 to 65.0 cm. A total of 38 fish captured off Vizhingam, India, were examined for fecundity by Muthiah (1985). Fecundity estimates for mature and ripe ovaries for fish in the 39.4 to 67.0 cm interval ranged from 202,000 to 1,570,000 ova.

Klinmuang (1978) estimated the fecundity of five kawakawa ranging in size from 39.5 to 51.0 cm from the South China Sea region. Fecundity for these fish averaged 1,730,000 ova and ranged from 585,000 to 2,593,000 ova.

These studies probably underestimate fecundity of kawakawa as the numbers of oocytes produced at the beginning of the spawning season is not fixed. Kawakawa is a multiple spawner releasing ova at frequent intervals during a spawning season.

Buñag (1956) and Rao (1964) concluded from the polymodal distribution of ova diameters that kawakawa spawned more than once during a spawning season. However, they were not able to determine frequency of spawning. An indication of spawning frequency can be obtained from a study on the reproductive biology of Euthynnus lineatus from the eastern Pacific. Schaefer (1987b) estimated the frequency of spawning from the proportion of sampled females with ovaries containing hydrated oocytes. E. lineatus was found to spawn at average intervals of 2.1, 5.7, and 3.6 days off the coasts of Mexico, Central America, and South America, respectively.

Kawakawa was the first tuna species to be successfully spawned in captivity (Kaya et al., 1981). Females and males kept in captivity for 2–4 weeks and about 4 months, respectively, at the Kewalo Research Facility, National Marine Fisheries Service, Honolulu Laboratory, were used in the experiments. Fish were induced to spawn with injections of salmon pituitary (SP), human chorionic gonadotropin (HCG) and pregnant-mare serum gonadotropin (PMS). Fish spawned after the second treatment with the higher dosages of the hormones.

5.3 Sex Ratio

Sex ratios for kawakawa from various areas are given in Table 2.

Williamson (1970) reports kawakawa in the size range from 24 to 73 cm occurring in the Hong Kong area. He found males and females of all lengths within this range, but the males accounted for 67 percent of the fish in the 50- to 73-cm interval. The dominance of males at sizes larger than 50 cm also occurs in the Philippines, Seychelles, and India (Table 3).

Table 2. Sex ratios of kawakawa.

Table 3. Numbers of male and female kawakawa by length intervals.

¹ - from Wade, 1950b
² - from Steinberg et al., 1982
³ - from Muthiah, 1985

6. DISTRIBUTION AND MIGRATION

6.1 Distribution

Kawakawa are widely distributed in the tropical and subtropical waters of the Indo-Pacific region (Figure 4). In the Indian Ocean, this species extends from Cape St. Francis, South Africa (Smith and Heemstra, 1986), along the coasts of east Africa, Arabian Peninsula, the Indian sub-continent, and Malaysian Peninsula. It is also found in the Red Sea, Persian Gulf, and off islands in the Indian Ocean, including Madagascar, Comoros Islands, Mauritius, Reunion, Seychelles, Lakshadweep, Andaman Islands, Nicobar Islands, Sri Lanka, and Maldives (Williams, 1963).

Figure 4. Distribution of kawakawa in the Indo-Pacific region.

Kawakawa are distributed throughout the Indonesian and Philippine archipelagos and off Papua New Guinea.

In the western Pacific Ocean, this species is distributed along the Asian continent from the Malaysian Peninsula eastward to southern mainland China. It is also found off southern Japan, where it is common along the Pacific Ocean coast to about 34°N latitude, but rare along the Japan Sea coast (Kikawa et al., 1963). This species is found throughout the islands of the Pacific Ocean including Caroline Islands, Marshall Islands, Kiribati, Hawaii, Midway Islands, Line Islands, Marquesas Islands, New Caledonia, Vanuatu, and Tahiti (Yoshida, 1979). The southern, northern, and eastern limits of kawakawa in the Pacific Ocean are probably New Caledonia, Hawaii, and Marquesas Islands, respectively.

Kawakawa occurs off the west, north, and east coasts of Australia. The southern most limit of this species on the west coast is Murchison River in western Australia and on the east coast is Twofold Bay in New South Wales (Whitley, 1964).

Kawakawa is replaced by Euthynnus lineatus, in the eastern Pacific, but stray specimens have been captured in this region. A 361-mm kawakawa (fork length) was reported from Los Angeles harbour, California, in 1952 (cited in Schaefer, 1987a). A second specimen of 920 mm and 13.15 kg was captured with sport fishing gear off Clarion Island in the Revillagigedo group in December 1986. This specimen exceeds by 1.36 kg the previous record of the heaviest kawakawa (Schaefer, 1987a).

Kawakawa and Thunnus tonggol occur together off continents and large islands throughout the Indo-Pacific region from Somalia in the west to Japan and Papua New Guinea in the east. T. tonggol is generally dominant in areas with broad continental shelves such as the Gulf of Thailand (Supongpan and Saikliang, 1987), east coast of Peninsular Malaysia (Chee and Yasin, 1988) and north coast of Australia (Lyle, 1988). On the other hand, kawakawa are dominant in areas with narrow continental shelves such as Sri Lanka and the Philippines.

6.2 Migration

Kawakawa occurs off Iran from Bushehr in the Gulf to the Pakistan border in the Gulf of Oman. Highest concentrations of this species occur from Bushehr to Lengeh Island in the Gulf from November through February (Nikouyan, 1988). Kawakawa migrate out into the Gulf of Oman with the onset of summer and an increase in seawater temperatures and salinities in the Gulf. It is captured off Jask in the Gulf of Oman from April through September and returns into the Gulf in winter.

7. NATURAL MORTALITY

There are no estimates of the coefficient of natural mortality for kawakawa.

8. OCEANOGRAPHIC FEATURES ASSOCIATED WITH THE SPECIES

Kawakawa are essentially confined to the continental shelf. Of 309 kawakawa captured by trolling off the west coast of Thailand, 47 were taken in the inner-neritic (0 to approximately 50 m), 260 in the outer-neritic (approximately 50–200 m) and only two in the oceanic zone (depths greater than 200 m). Distribution of pole-and-line and troll catches indicated that small kawakawa in the 20- to 40-cm interval were distributed principally in the inner-neritic. Small fish begin leaving the inner-neritic with increasing size, and essentially all have moved into the outer-neritic after 40 cm (Yesaki, 1982).

Kawakawa are rarely captured beyond the edge of the continental shelf. Anderson (1988) reports that the bulk of the kawakawa catch in the Maldives is taken by traditional sailing craft trolling in and around the atolls. On the west coast of Thailand, kawakawa were found under a fish-aggregating device (FAD) deployed in 432-m depths (Lee, 1982). Frusher (1986) notes kawakawa were the most abundant species captured around FADs anchored in 160 m and 390 m off the northwestern coast of Papua New Guinea.

Kishinouye (cited in Yoshida, 1979) reported that kawakawa were found in waters with temperatures ranging from 18° to 28°C off the coast of Japan.

Williamson (1970) reports that sea-surface temperatures off Hong Kong range from 14° to 29°C throughout the year. The waters off the west side of Hong Kong are brackish because of the West River estuary, with surface salinities 33°/.. in February and 6°/.. in July. The waters on the east side are more oceanic, with surface salinities of 34°/.. and 26°/.. during these respective months. Concentrations of kawakawa are reported close inshore on the east side of Hong Kong during June-August and scattered fish occur in deep waters south of Hong Kong throughout the year. This species was not seen in inshore waters during the coldest months nor in brackish waters on the west side.

Mean sea-surface temperatures off the west coast of Thailand increased from a low of 28.6°C in December 1979–January 1980 to a high of 32.2°C in June, and thereafter decreased again to 28.6°C in November 1980 (Yesaki, 1982). Kawakawa were captured throughout the year off this coast, but the highest catches by pole-and-line fishing were made during February, March, and April (Lee, 1982) when sea-surface temperatures were rising.

9. INTERACTIONS WITH OTHER SPECIES

Kawakawa are captured with Thunnus tonggol and Auxis thazard throughout much of the Indo-Pacific region, including the north coast of Australia (Lyle and Read, 1985), Gulf of Thailand (Spongpan and Saikliang, 1987), west coast of Thailand (Yesaki, 1982), east coast of Peninsular Malaysia (Chee and Yasin, 1988), Bangladesh (Rashid, 1988), west coast of India (Silas et al., 1985a), Gulf of Oman coast of United Arab Emirates (Ali and Thomas, 1979), Oman (Prabhakar and Dudley, 1989), and southern Red Sea (Ben-Yami, 1968). This species is captured with Sarda orientalis off the north coast of Australia (Lyle and Read, 1985), west coast of India (Silas, et al., 1985a), and Oman (Prabhakar and Dudley, 1989). Kawakawa are associated with Megalaspis cordyla in the Gulf of Thailand (Supongpan and Saikliang, 1987), southern Red Sea (Ben-Yami, 1968) and east Africa (Williams, 1963). Kawakawa also co-occurs with T. albacares and Katsuwonus pelamis in the coastal waters of Sri Lanka (Sivasubramaniam, 1970) and with K. pelamis and Elagatis bipinnulata off Papua New Guinea (Wilson, 1981). All these species are probably competitors of kawakawa.

Argue et al. (1983) examined stomach contents of pelagic species captured by pole and line for occurrence of juvenile tunas. They found juveniles kawakawa in stomachs of K. pelamis, T. albacares, and kawakawa (Table 4). The occurrence of juvenile kawakawa in K. pelamis stomachs was significantly higher after 1500 hours than earlier in the day. However, the occurrence of juvenile kawakawa in K. pelamis stomachs did not differ with respect to distance from land.

Table 4. Number and incidence of kawakawa juveniles in the stomachs of predators sampled from tropical waters (modified from Argue et al., 1983).

Other scientists have reported predation of juvenile kawakawa by tunas. Ronquillo (1953) and Nakamura (1965) noted the presence of kawakawa in the stomachs of K. pelamis. Kumaran (1967) found a 10.0-cm kawakawa with a 3.8-cm kawakawa in its stomach. Kawakawa appears to be cannibalistic during much of its life cycle.

Tetrapterus audax and Carcharinus sp. are predators of kawakawa off the east coast of Africa (Williams, 1963). Carcharinus sorrah preys on kawakawa off the north coast of Australia (Stevens and Wiley, 1986).

10. GENERAL DESCRIPTION OF THE FISHERIES

There are no specific fisheries for kawakawa, but rather fisheries that aim for small tunas, which generally include kawakawa, T. tonggol, A. thazard,, and S. orientalis. Descriptions of purse-seine, gillnet, and troll fisheries for small tuna in the South China Sea are given in the “Interactions between fisheries for small tunas off the South China Sea coast of Thailand and Malaysia” included in this volume (Yesaki, 1993).

11. TRENDS IN CATCH, FISHING EFFORT, AND CATCH PER UNIT OF EFFORT

11.1 Annual Catches

Nominal catches of kawakawa have increased from 55,000 mt in 1979 to 128,000 mt in 1988 (Table 5). This doubling of the reported catches in the 11-year period resulted in part from improved statistics collecting and reporting systems in several countries, but for the most part from higher catches in most countries. The most pronounced increases in kawakawa catches were made in Thailand, Malaysia, and Philippines.

11.2 Fishing Effort and Catch per Unit of Effort

The only fishery for which there is a relatively long time-series of effort and catch statistics for kawakawa is the troll fishery off the South China Sea coast of Malaysia. The average number of trips per month by troll-line vessels based in Terengganu declined from 194 trips during the 1982–1985 interval to 146 trips during the 1987–1989 interval (Figure 5). There was a corresponding decrease in kawakawa catches from 22.6 mt to 12.4 mt and in catch rates from 117 to 85 kg/trip during these respective intervals.

12. POPULATION DYNAMICS

No information is available on this subject.

13. INTERACTIONS BETWEEN FISHERIES

Kawakawa differs from most of the other tunas in that almost the entire life cycle is completed in the neritic regime. Larvae, juveniles, preadults, and adults are found over the continental shelf, where fisheries are generally highly developed. Distribution in areas of intense fishing effort for small-pelagic species results in incidental catches of juvenile kawakawa. Juvenile kawakawa are captured in small-mesh gillnets in Sri Lanka, by purse-seine fisheries off the South China Sea coast of Thailand and Malaysia, and by ringnet (Jabat and Dalzell, 1988), and bagnet (Arce, 1987) fisheries of the Philippines. The incidental captures of juvenile and preadult kawakawa may be the most significant factor affecting the productivity of kawakawa stocks.

Table 5. Landings in metric tons of kawakawa in the Indo-Pacific region by country and year.

Source - IPTP, 1991
¹ - SEAFDEC, 1981; 1982; 1983; 1984; 1985; 1986; 1987; 1988; 1989; 1990

² - FAO, 1981; 1984; 1989

* estimated - INDIA - 1979/1980 - 65% of TUN (% from 1981 - LOT+KAW+SKJ+FRZ+TUN)
- MALAYSIA - 1979/1983 - 10% of TUN (% from 1984 - LOT+KAW+TUN)
-                     - 1989 - 43% of TUN (% from 1988 - LOT+KAW+FRZ+TUN)
- PAKISTAN - 1979/1984 - 12% of KAW+SKJ (% from 1986 - YFT+LOT+KAW+FRZ+TUN)
- SRI LANKA - 1979/1983, 1985 - 44% of TUN (%from 1984 - KAW+FRZ)
- THAILAND - 1979/1986 - 61% of TUN (% from 1987 - KAW+FRZ)

Figure 5. Catch, effort and catch per unit of effort of kawakawa for troll-line vessels based in Terengganu, Malaysia.

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