Striped Marlin

fieldmarks: Anterior lobe of first dorsal fin pointed and higher than remainder of the fin, the height decreasing gradually backward; anus situated near origin of first anal fin, the distance between them smaller than half of anal fin height; tips of pectoral and first anal fins pointed. Body elongate and fairly compressed. Bill stout and long, round in cross section; nape fairly elevated; right and left branchiostegal membranes completely united to each other, but free from isthmus; no gillrakers; both jaws and palatines (roof of mouth) with small, file-like teeth. Two dorsal fins, the first with 37 to 42 rays, usually with a pointed anterior lobe, higher than (or occasionally equal to) body depth anteriorly, the fin then abruptly decreasing in height to about the 10th dorsal fin ray and gently decreasing further backward; first dorsal fin base long, extending from above posterior margin of preopercle to just in front of second dorsal fin origin; second dorsal fin with 5 to 6 rays, its position slightly backward in respect to the second anal fin; two anal fins, the first with 13 to 18 rays, the second with 5 or 6 rays and very similar in size and shape to the second dorsal; pectoral fins long and narrow, with pointed tips, adpressible against sides of body and with 18 to 22 rays; pelvic fins slender and almost equal to, or slightly shorter than the pectorals in large specimens, and slightly longer than pectorals in smaller individuals. Caudal peduncle well compressed (laterally) and slightly depressed (dorsoventrally), with a pair of keels on each side and a shallow notch on both, the dorsal and ventral surfaces; anus situated just in front of first anal fin origin. Lateral line single and obvious, curving above base of pectoral fin and then continuing in a straight line toward the caudal fin base. Body densely covered with elongate bony scales, each with 1 or 2 posterior points. Vertebrae 24 (12 precaudal and 12 caudal). Colour: body blue-black dorsally and silvery white ventrally, with about 15 rows of cobalt-coloured stripes, each consisting of round dots and/or narrow bands. First dorsal fin dark blue; other fins usually dark brown, sometimes tinged with dark blue; bases of first and second anal fins tinged with silvery white.

T. audax occurs mainly in the tropical, subtropical and temperate waters of the Pacific and Indian oceans. Japanese long line catch data collected over many years show that the distribution pattern of this species within the Pacific Ocean is horseshoe-shaped, with the base of the horseshoe located along the Central American coast. T. audax is occasionally found on the Atlantic side of the Cape of Good Hope (Talbot & Penrith, 1962) and one individual was caught off Angola, West Africa in October 1976, having probably strayed from the Indian Ocean as in a few cases of Tetrapturus angustirostris and Makaira indica. The latitudinal range limits of T. audax, based on data from the commercial longline fishery, extend from about 45° N in the North Pacific to 30° S in the eastern South Pacific and to 45° S in the western South Pacific, as far south as 45° S in the southwestern Indian Ocean and 35° S in the southeastern Indian Ocean.

The maximum size attained by this species exceeds 350 cm in total length and 200 kg in weight. The all tackle angling record is a fish caught off the Cavalli Islands, New Zealand, on 14 January 1977, weighing 189.37 kg (417 lb 8 oz). Other records of large specimens (over 180 kg) are the following: 183.47 kg (404 lb 8 oz), Bay of Islands, New Zealand, on 12 March 1980; 181.89 kg (401 lb), Cavalli Islands, New Zealand, 24 February 1970; 180.53 kg (398 lb), Mayor Island, New Zealand, 30 December 1974 (IGFA, 1981). All world records for both men and women recognized by IGFA are from New Zealand, except a record from Botany Bay, Sydney, on 24 October 1976 (161.93 kg=357 lb for men's 30 lb line class). Size at first capture (longline fisheries) of T. audax is approximately 80 cm eye-fork length (= 83.9 to 86.1% of body length). Around Taiwan Island, size at first maturity is generally estimated between 140 cm and 160 cm eye-fork length, and the biological minimum size of males at about 137 cm eye-fork length. The maximum size in commercial fisheries is probably about 290 cm eye-fork length or 258.6 kg (570 lb). The sizes of fish taken by commercial longliners range mainly from 205 to 225 cm body length in the northern part of the western North Pacific, between 145 and 185 em body length in the southern part of the western North Pacific, between 235 and 255 cm body length in the central North Pacific, and about 280 cm body length in the western South Pacific.

This is an epipelagic andoceanic species,usually swimming above the thermocline. Parin (1968) included it among the holoepipelagic species which inhabit the isothermic, surface-pelagic layer of the ocean at all stages of their life cycle, and are usually confined to tropical and subtropical waters where permanent thermoclines exist, but penetrate higher latitudes in the local warm seasons. However, the striped marlin has a somewhat atypical distribution as compared to most other billfishes and tunas, and seems to prefer more temperate waters. In the Pacific, its distribution resembles that of the albacore (Thunnus alalunga ) and the bluefin tuna (Thunnus thynnus ), in contrast to that of the other billfishes and tunas. In the Indian Ocean, however it is found in warmer waters. The total distributional range of this species, is generally bounded by the 20° and 25° C isotherms, at least in the western Pacific Ocean. This is the most dominant and widely distributed of all billfishes, especially in the eastern and northcentral Pacific, where it is much more abundant than in the western Pacific. In the Indian Ocean, the striped marlin is abundant in the western Arabian Sea. Larvae of striped marlin have been recorded from the western North Pacific west of 180° long.) between 10° to 30° N, and from the central South Pacific (west of 130° W) between 10° and 30° S. They are most abundant in the respective local early summers, with peak occurrences during May through June in the western North Pacific, and in November and December in the central South Pacific. The seasonal occurrence of mature females coincides with that of the larvae. While the distribution of larvae for the eastern Pacific (east of 120° W) is not known, mature fish are reported to occur there between 5° and 20° N, largely in May and June. Larvae have also been reported to occur in the Banda and Timor seas in January and February, in the eastern Indian Ocean in October and November between 6° N and 6° S, and in the western Indian Ocean between 10° S and 18° S in December and January. Mature females are found in March and May in the Bay of Bengal, although larval occurrence is not yet known there.The lower temperature limit in the distribution of larvae is approximately 24° C, both in the Indian and Pacific oceans. However, larval distributions in the two oceans differ in that, in the Pacific, the larvae of this species are scarcely found in equatorial waters. It has been noted that larvae of T. audax are not likely to appear in the Kuroshio Current area, while those of the Indo-Pacific sailfish, Istiophorus platypterus occur there extensively. Two juveniles of striped marlin (12.2 and 14.5 cm body length) were found in stomachs of a yellowfin tuna (Thunnus albacares ), and of a dolphinfish (Coryphaena hippurus ) taken by longlines on 13 January 1955 at 23°52' S/175°49' W and on 21 December 1964 at 17°5' S/67°29' E. These two occurrences coincide with larval distributions of the species in the South Pacific and Indian oceans, respectively. The ovarian eggs of striped marlin from New Zealand average about 0.85 mm in diameter shortly before spawning. The size of ovulated eggs is presumed to exceed 1 mm in diameter, considering that the mean diameter of the eggs of the shortbill spearfish (Tetrapturus angustirostris ) is 1.442 mm and that the eggs of the Indo-Pacific sailfish (Istiophorus platypterus ), measure 1.304 mm in diameter. T. audax, like the other marlins, does not form dense schools like the tunas, and the individuals are usually dispersed at considerably wide distances. Several fish, however, are often seen together, sometimes following one another, especially during the spawning season. Surfacing is apparently more common with strong wind and high waves. When wind and current are moving in the same direction, the water surface is rather smooth, but when the wind runs against the current, high waves develop and this is when striped marlin are most often seen at the surface around Taiwan Island, usually swimming in the direction of the wind. When surfaced, striped marlins usually swim very slowly, with the upper caudal fin lobe above the surface and the dorsal fin retracted and not showing, a characteristic which reportedly distinguishes thern from swordfishes which are unable to depress the dorsal fin and show both the dorsal and caudal fins when surfaced. Striped marlins swim faster and are less easily approached when surfaced than the swordfish. Like other billfishes and tunas, they tend to school by size. [more...] Dolphinfishes (Coryphaena spp.), wahoo (Acanthocybium solandri ) and the pelagic large sharks (Prionace, Isurus, Lamna, Carcharhinus and Alopias ) feed on many of the same forage organisms as the striped marlin. Its closest competitors for food are possibly the other billfishes and larger tunas. The striped marlin, however, tends to feed more on epipelagic organisms and less on mesopelagic ones than the swordfish and the oceanic tunas. Food habits do not appear to vary significantly with sex or size, at least in adults. Considerable variation in species composition of the diet occurs, however, with seasons and geographic localities. T. audax, like other billfishes and tunas, is thought to be carnivorous and a non-selective feeder. Some of its reported major forage species by localities are: Fistularia sp., Auxis sp., squid (East Africa); Scomberoesox saurus, Arripis trutta, Loligo sp., Ommastrephes sloani, Caranx lutescens, Scomber japonicus (New Zealand); Alepisauridae, Clupeidae (Tasman Sea); Gempylus serpens, Cololabis saida, Engraulis mordax, Sardinops caerulea, Trachurus symmetricus (California); Etrumeus teres, Fisturalia sp., Argonauta sp., squid Mazatlan, Mexico, Etrumeus teres, Scomber japonicus, Fistularia sp., squid (Baja California, Mexico); Auxis spp., Bramidae, Gempylidae, squid (eastern North Pacific); Alepisaurus spp., squid (eastern South Pacific); squid (Peru-Chile); Engraulis rinqens, Trachurus symmetricus, squid (Chile).Predators of adults of this species are probably extremely rare or almost inexistent, the only likely candidates being some of the large pelagic sharks and the toothed whales, although there are many predators to the earlier life-stages of the striped marlin.

In the period from 1978 to 1982, catches of T. audax have been reported from seven FAO Fishing Areas (51, 57, 617 71, 77, 81 and 87), mostly by Japan and the Republic of Korea. The total world catch was 15 426 t in 1978, 15 988 t in 1979, 18 429 t in 1980, 15 664 t in 1981 and 15 460 t in 1982. Only 13.6% (2 132 0 of the 1981 total catch was taken in the Indian Ocean, and 86.4% (13 532 t) in the Pacific Ocean, particularly in Fishing Area 61 (northwest Pacific) with 7 229 t predominantly by Japan, in Fishing Area 77 (eastern central Pacific), with 2 414 t predominantly by Japan, and in Fishing Area 87 (southeast Pacific) with 2 217 t by Japan and the Republic of Korea (FAO, 1983); of the 1982 catch, 12.6% (1 949 t) was taken in the Indian Ocean and 87.6% (13 511 t) in the Pacific Ocean, predominantly by Japan, China (Taiwan Province) and the Republic of Korea (FAO, 1984). The commercial catch of T. audax is taken mostly by surface longlining, while harpooning may be responsible for less than 1% of the total catch in recent years. The longliners aim chiefly at tunas and marlins which are frequently swimming at depths between 100 and 150 m. Longline gear consists of a mainline, float lines, branch lines, hooks, bouys including several radio-bouys, and flags. Several hundred of these units (each unit is referred to as a "basket") are joined in a series to make up a set of longline. The longline is retrieved with a line hauler. Japanese longliners in the eastern Pacific use about 2 000 hooks (about 400 baskets) per set. Due to recent manpower problems, considerable effort has been directed toward developing labour-saving devices in longlining. The reel-type and the tub-type of longlining are two examples of this development. In the reel-type the mainline (usually wire) is continuous and reeled onto a large drum, while in the tub-type, the retrieved line is coiled into a large tub. In harpooning, the electric harpoon has been recently introduced in Japanese fisheries to speed up the killing of the fish. The total catch reported for this species to FAO for 1999 was 9 717 t. The countries with the largest catches were Japan (5 532 t) and Taiwan Province of China (2 696 t). The quality of the flesh is the best among billfishes for sashimi and sushi. It is marketed mostly frozen, sometimes fresh.