Indo Pacific Sailfish

fieldmarks: First dorsal fin sail-like and remarkably higher than greatest body depth; pelvic fins very long, nearly reaching to anus, with a well developed membrane. Pectoral and caudal fins short compared with those of Istiophorus albicans in young up to about 90 cm body length. Body fairly compressed. Bill long, slender and round in cross section; jaws and palatines with small, file-like teeth ; no gillrakers; right and left branchiostegal membranes united to each other, free from isthmus. Two dorsal fins, the first large with 42 to 49 rays, the second small with 6 or 7 rays; first dorsal fin sail-like, with the middle rays longest, remarkably higher than body depth at level of midbody, its base long and close to that of second dorsal fin; two anal fins, the first with 12 to 17, the second with 6 or 7 rays; position of second anal fin slightly more forward than that of second dorsal fin; pectoral fins with 18 to 20 rays, relatively shorter than in I. albicans in immature specimens (to about 90 cm body length); pelvic fins extremely long, almost reaching to anus, depressible into a groove, with one spine and several soft rays fused tightly together and with a well developed membrane. Caudal peduncle with double keels on each side and a shallow notch on both, the dorsal and the ventral surfaces; anus situated near to first anal fin origin. Lateral line single and well visible. Scales varying in shape with growth; in adults they are somewhat sparse, imbedded in the skin, each with a single, rather blunt point, or with two posterior points. Vertebrae 24 (12 precaudal and 12 caudal). Colour: body dark blue dorsally, light blue splattered with brown laterally, and silvery white ventrally; about 20 rows of longitudinal stripes on sides, each stripe composed of many light blue round dots. Bases of first and second anal fins often tinged with silvery white; membrane of first dorsal fin dark blue or blackish blue, with scattered small, round black dots; remaining fins blackish brown or dark blue.

I. platypterus is widely distributed in the tropical and temperate waters of the Pacific and Indian oceans. Its latitudinal range, based on data from longline catches, is approximately 45° to 50° N in the western North Pacific, 35° N in the eastern North Pacific, 40° to 35° S in the western South Pacific, 35° S in the eastern South Pacific, 45° S in the western Indian Ocean, and 35° S in the eastern Indian Ocean.This species shows a strong tendency to come close to the shore, even though a few individuals have been caught in the central parts of the oceans. Large numbers of Indo Pacific sailfish are found in waters off Papua New Guinea, around the Solomon Islands, in the warm Kuroshio Current and its branch, the Tsushima Current, in the Sea of Japan, in the East China Sea, around the Philippines, in the Banda Sea, in the central South Pacific from Tahiti to the Marquesas, and off the Pacific coast of Mexico. They are also fairly abundant off the northern coast of Australia and around the Hawaiian Islands, India and Sri Lanka, but have been seldom seen off the Pacific coast of South America from Peru to Chile. This species has also entered the Mediterranean Sea from the Red Sea through the Suez Canal.

This species reaches a maximum size beyond 340 cm in total length and 100 kg in weight. In the sports fishery (all tackle angling record) corresponds to a fish of 327.7 cm total length and 100.24 kg (221 lb) weight, taken at Santa Cruz Island, Galapagos, Ecuador on 12 February 1947. Another very large fish (340.4 cm total length and 89.81 kg (198 lb) weight) was taken at La Paz, Baja California, Mexico on 23 August 1957. Other records over 85 kg are the following: 90.26 kg (199 lb) at Pinas Bay, Panama on 17 January 1968; 89.81 kg (198 lb) at Mazatlan, Mexico on 10 November 1954; 87.54 kg (193 lb) at Acapulco, Mexico on 8 January 1978; 87.28 kg (192.7 lb) at Acapulco, Mexico on 4 October 1961; 87.09 kg (192 lb) at La Paz, Baja California, Mexico on 6 September 1950; and 85.72 kg (189 lb) at Yanuca, Fiji on 7 December 1967 (IGFA, 1981). All-line-class world records up to 1981 for both men and women recognized by IGFA are from the eastern Pacific, except the one for the women's 130-lb line class of 189 lb already mentioned from Yanuca, Fiji. In sportsfishing at Malindi, Kenya, the majority of individuals caught ranged from 203 to 254 cm fork length (224 to 279 cm total length) and from 18.1 to 47.2 kg in weight. Length frequency data for sailfishes caught by longlines in the East China Sea, give size range from 105 to 240 cm body length (60% between 165 and 190 cm body length); the size distribution is essentially unimodal, except in June when a group of 125 to 150 cm fish suddenly appeared in the catch. Koto, Furukawa & Kodama (1959) believed that these small fish enter the East China Sea from other areas during this month. The average size of the individuals caught by longlines is unimodal, about 140 to 240 cm body length, while it is bimodal in those caught by driftnets and setnets, about 50 to 110 cm and 140 to 240 cm body length, respectively.

The Indo-Pacific sailfish is an epipelagic and oceanic species,usually found above the thermocline. It shows a strong tendency to approach continental coasts, islands and reefs.In the western Pacific, the distribution of postlarvae and adults appears to be closely related to the Kuroshio Current, and the densest concentrations seem to coincide with the spawning season. Individuals over 160 cm eyefork length (= 84 to 88.7% of body length) migrate southward out of the East China Sea, presumably for spawning.In the eastern Pacific, the seasonal north-south displacements of this species off the coast of Mexico appear to coincide with the seasonal movements of the 28° C water isotherm. In the Indian Ocean, off East Africa, the abundance and distribution of I. platypterus is positively correlated with the months of the northeast monsoons when the East African Coastil Current reaches its maximum temperature (29° to 30° C) and minimum salinity (35.2 to 35.3°/oo). This is also the time of highest biological productivity in the surface waters caused by a mixing of waters resulting from the junction of the southward-flowing Somalia Current and the northward-flowing East African Coastal Current. In the Sea of Japan, considerable numbers of individuals of this species migrate in schools northward with the warm Tsushima Current (a branch of the Kuroshio) during summer (peak in later summer), and southward against the current during autumn (peak in early autumn), and are caught in these periods by the coastal setnets. These schools consist of young (55 to 110 cm body length) and adults (145 to 235 cm body length) with no fish of intermediate sizes caught by the setnets. Sometimes the young and the adults are mixed in the catches, but more often they are landed separately. Therefore, I. platypterus most likely schools by size. Usually, the young form more dense schools than the adults. In the East China Sea, the Indo-Pacific sailfish migrates northward in summer and returns southward in autumn where it overwinters in the southernmost area; fish under 160 cm eye-fork length move into the area between May and July while those over 160 cm migrate southward out of the area, probably for spawning. Spawning of this species occurs with males and females swimming in pairs or with two or three males chasing a single female (probably mating behaviour). I. platypterus seems to spawn throughout the year in tropical and subtropical waters of the Pacific with peak spawning occurring in the respective local summer seasons. The ripe ovarian eggs are about 0.85 mm in diameter and have a single oil globule surrounded by a pale yellow indefinite nimbus; there are no structures on the vitelline membrane and the egg as a whole is transparent or translucent. Eggs shed from a captured female in the Indian Ocean averaged 1.304 mm in diameter. The feeding behaviour of I. platypterus has been observed by fishermen as follows: when one or several sailfish found a school of prey fishes (sardines, anchovies, mackerels, or jack mackerels), they began to pursue it at half speed with their fins half- folded back into the grooves. They then drove at the prey at full speed with their fins completely folded back and once they had caught up with it, they suddenly made sharp turns with their fins expanded to confront a part of the school and then hit the prey with the bill. Subsequently they ate the killed and stunned fish, usually head first. Surprisingly, several individuals showed a kind of team-behaviour in capturing the prey. I. platypterus and Makaira indica are the billfish species dominantly migrating into inshore waters and they undoubtedly compete with each other for food and habitat, although M. indica probably feeds on larger forage organisms, and swims a little deeper and farther offshore than the sailfish. The habitat of this species is strikingly different from that of the closely related Tetrapturus angustirostris which does not usually occur within 500 km off the coast, while M. indica is mostly distributed within this range. The major forage items of the Indo-Pacific sailfish are fishes and squids, but the adults are fairly opportunistic feeders and take almost any food they come across. During several longline cruises of Japanese research vessels in the eastern North Pacific Ocean, adult I. platypterus have been shown to feed mainly on cephalopods and fishes (Bramidae, Stromateidae, Carangidae, Ostracion spp., Gempylidae, Auxis spp., Trachipterus spp., Belonidae, Balistidae, Coryphaena spp., Lagocephalus spp., etc.).Large pelagic sharks, the killer whale and other related species attack billfishes and tunas hooked by longlines, but predation on free-swimming tunas and billfishes is thought to be very rare.

In the period from 1978 and 1982 catches of I. platypterus have been reported from seven FAO Fishing Areas (51, 57, 61, 71, 77, 81 and 87), predominantly by Japan and the Republic of Korea. The total world catch was 10 516 t in 1978, 7 916 t in 1979, 7 767 t in 1980, 6 438 t in 1981 and 7 214 t in 1982. Only 4% (285 t) of the 1982 total world catch were taken in the Indian Ocean, and 96% (6 929 t) in the Pacific Ocean, particularly in Fishing Areas 61 and 77 (northwest Pacific and eastern central Pacific) of which 6 218 t were taken by Japan, China (Taiwan Province) and the Republic of Korea. In Fishing Area 77 (eastern central Pacific), the Korean and Japanese landings have decreased remarkably in recent years: 5 425 t (1978), 4 351 t (1979), 1 525 t (1980), 539 t (1961) and 2 483 t (1982) (FAO, 1984). It should be noted that the catch statistics given for this species by Japanese longliners include Tetrapturus angustirostris, but that the share of the latter species in these catches is quite negligible. The total catch reported for this species to FAO for 1999 was 18 701 t. The countries with the largest catches were Sri Lanka (6 979 t) and Taiwan Province of China (3 610 t). Indo-Pacific sailfish are often taken as bycatch by the commercial surface tuna longliners. They are also caught by commercial fishermen with surface driftnets, and by trolling, harpooning and setnetting. In sportsfishing this species is caught by surface trolling. The flesh is dark red, and not as good as that of marlins. In summer it is good for sashimi (sliced flesh with soy-sauce and horse radish) or sushi (vinegared boiled rice with sliced flesh and horse radish, dipped in soy-sauce during the meal).