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Black marlin fishing: the marlin that cannot fold its pectoral fins

Almost every fish can fold its pectoral fins against its body. The black marlin cannot: they stand out rigidly, their joint is, according to the Japanese Wikipedia, fixed and immovable, and according to the English Wikipedia — especially from around 68 kg — they can no longer be pressed flat against the sides, only tilted backwards a little. That is exactly how you tell it apart from the blue marlin for certain. This article is about the black marlin, *Istiompax indica* — in German Schwarzer Marlin, in Spanish marlín negro, in Italian marlin nero, in French makaire noir, in Portuguese marlim-preto, in Dutch zwarte marlijn, in Finnish mustamarliini, in Swedish and Norwegian svart marlin, in Russian чёрный марлин, in Japanese シロカジキ (shirokajiki).

The only one of its genus

The black marlin belongs to the billfishes (Istiophoridae), like the blue marlin, the white marlin, the striped marlin, the sailfish and the Mediterranean spearfish, to each of which this series devotes a group of its own. It was described in 1832 by the French zoologist Georges Cuvier, then as *Tetrapturus indicus* (English, Spanish Wikipedias). For a long time it stood in the genus *Makaira*, the genus of the blue marlin; today it is the only species of the genus *Istiompax* (German, French, Italian Wikipedias). According to the German Wikipedia, this genus is the sister of *Kajikia* — the white and the striped marlin.

According to FishBase it is a pelagic, oceanic fish that usually lives in surface waters above the thermocline — but, unlike its relatives, often close to land, near islands and coral reefs. The Japanese Wikipedia writes that, after the sailfish, it is the marlin most likely to turn up near the coast. According to the English Wikipedia, in one population studied it spent up to 87 % of its time in the upper 30 m at night, but less than 60 % by day. Young black marlin off Australia use the lagoon of the Great Barrier Reef as a nursery and gather there seasonally (English Wikipedia).

Its prey: fish, squid, cuttlefish, octopus and large crustaceans — and, when they are abundant, mostly small tunas (FishBase). The Japanese Wikipedia calls it one of the few predators of the skipjack tuna; hence its nickname カツオクイ (katsuo-kui, “skipjack eater”). According to the English Wikipedia it prefers mackerel scad; in some stomachs researchers have even found young sharks. It swallows its prey head first, and because prey from its stomach often shows slashes from the bill, it is believed to use its bill when hunting inside a school (English Wikipedia). Off Malaysia, according to the Russian Wikipedia, its diet consisted mainly of anchovies, jacks, flying fish and squid.

How to recognise it

An elongated body, according to FishBase not very compressed — the most solid of all marlins — with a short, heavy bill (FishBase, German and English Wikipedias). Behind the eyes the back rises steeply up to the first dorsal fin; hence its Japanese nickname カタハリ (katahari, “broad shoulders”). The first dorsal fin is highest at the front but does not reach the depth of the body (FishBase, German, Italian and Russian Wikipedias) — in the striped marlin it is the other way round. The pectoral fins are sickle-shaped and rigid and cannot be folded: the surest feature. According to the English Wikipedia it is also the only billfish in which the second dorsal fin starts ahead of the second anal fin, at every size. The back is dark blue to blue-black, the belly silvery white, the first dorsal fin blackish to dark blue without spots, the other fins dark brown (FishBase). The skin carries small, embedded scales with one or two sharp points (FishBase, German Wikipedia).

What separates it from the blue marlin, according to the English Wikipedia: the blue marlin’s pectoral fins point more to the side, the black marlin’s more downwards; the black is larger and has none of the faint light-blue vertical stripes. From the striped and the white marlin it is separated by their distinct stripes, which it lacks.

  • Size: FishBase gives 465 cm fork length as the maximum, 380 cm as the common length and 750 kg as the heaviest published weight. According to the Japanese Wikipedia that makes it the heaviest of all marlins; fish over 120 to 130 kg are almost always females.
  • The record: In August 1953, off Cabo Blanco in Peru, Alfred C. Glassell Jr. caught a black marlin of about 710 kg (1,560 lb) — according to the English Wikipedia still a record under IGFA rules as of 2023. The fish is preserved and on display in Washington.
  • Spawning: According to FishBase it prefers to spawn at 27 to 28 °C; one ripe female carried about 40 million eggs. The Russian Wikipedia calls it a batch spawner.

Where it lives — and the fish of Camogli

FishBase: in tropical and subtropical waters of the Indo-Pacific, occasionally in temperate ones, between 44° North and 47° South, at 15 to 30 °C. A highly migratory fish. According to the Italian Wikipedia it occurs along the coast of East Africa, from South Africa to Djibouti, around Madagascar and the Seychelles, and in the eastern Pacific from California to Chile. The Russian Wikipedia names the East China Sea, the inner seas of Indonesia and the coasts of Mexico and Central America as places where it is particularly common. According to FishBase, stray individuals migrate around the Cape of Good Hope into the Atlantic — but a breeding stock there is unlikely.

And the Mediterranean? The Italian Wikipedia reports a single find: in 1987 a black marlin was caught at Camogli in the Ligurian Sea, probably having come in through the Strait of Gibraltar — and calls it very rare there. For an angler from Europe it remains a travel fish. According to the English Wikipedia it is fished above all off South America, Southern Asia and Australia; the Japanese Wikipedia calls the trolling off Cairns famous — and writes that commercial catch and sale of its meat are banned there. According to the Russian Wikipedia, most sport anglers today release the marlin they catch.

On the plate

According to FishBase its flesh is of good quality; it is sold chilled or frozen and prepared as sashimi in Japan. The Japanese Wikipedia writes that its flesh is red and considered tastier than the blue marlin’s, in season in winter. The Russian Wikipedia calls it a delicacy of expensive restaurants. In the United States, the Billfish Conservation Act of 2012 bans the sale of marlin — not fishing for it (English Wikipedia).

Eight contradictions, left standing

  • How fast is it? The Finnish Wikipedia: around 130 km/h. The Portuguese: 120 km/h. The Dutch: about 90 km/h. The French: 40 to 60 km/h over short distances. The English and the Italian cite a 2016 study that calculates, from muscle contraction times, a theoretical upper limit of only about 36 km/h — and treat figures like 129 or 132 km/h as exaggerations.
  • How heavy does it get? FishBase and most Wikipedias: 750 kg. The English: possibly up to 900 kg. The French: up to one tonne. The German: females normally up to 650 kg. And the common length: 380 cm (FishBase, Italian Wikipedia) — or about 1.8 to 2.7 m (English Wikipedia, “6–9 ft”).
  • How deep does it swim? FishBase: 0 to 915 m, usually 0 to 200 m. The German: to more than 900 m. The Italian: usually no deeper than 100 m, but down to 950 m. The English: down to about 500 m. The Portuguese: not far below the surface.
  • Does it live in the Atlantic? FishBase and the German, English, Italian and Japanese Wikipedias: only strays come round the Cape, and spawning in the Atlantic is not recorded. The Finnish: neither in the Atlantic nor in the Mediterranean. The Italian, on the other hand, knows the catch from Camogli. And the Portuguese and the Dutch Wikipedias simply count the Atlantic among its oceans.
  • Does it have stripes? FishBase: sometimes light-blue vertical stripes. The German: occasionally; most are unmarked. The Russian: adults have no stripes, only the juveniles. The English: it lacks the faint stripes of the blue marlin. The Italian: sometimes darker bands on the belly.
  • How old does it get? The Italian Wikipedia: up to 12 years. The Japanese: 10 to 13 years. The English: females live longer than males and are larger from about age 5 — before that, smaller.
  • Is it threatened? FishBase and the Italian and Spanish Wikipedias: the IUCN lists it as Data Deficient. The English: its status is unknown — partly because it is particularly good at shedding its trackers. The Portuguese: in 2010 Greenpeace put it on its red list. The Dutch: enormously overfished.
  • Is there a fishery for it? The English Wikipedia: “currently no fisheries”. The Italian: about 5,000 tonnes a year. The Russian: 2,200 to 6,400 tonnes a year in the 1970s to 1990s, mainly by Japan, Indonesia and Taiwan, with longlines, by trolling and with handlines.

Five names that lead to the wrong fish

  • “シロカジキ” — the “white” marlin. In Japanese the black marlin is called shirokajiki, literally “white marlin”. According to the Japanese Wikipedia, the English name refers to the dark back of the living fish, the Japanese one to its whitish colour after death. The English white marlin, by contrast, is a different fish altogether: the Atlantic white marlin, Japanese ニシマカジキ, to which this series devotes a group of its own.
  • “クロカジキ” — the “black” marlin. Conversely, in Japanese the blue marlin is called kurokajiki, literally “black marlin”. Search in Japanese for the black marlin and you land on the blue — search for the white and you land on the black.
  • “Makaira indica”. It still stands under this old name in the Portuguese Wikipedia and many older sources. But *Makaira* is today the genus of the blue marlin; the black marlin stands alone in *Istiompax*.
  • “Marlijn”. The Dutch Wikipedia files the black marlin under the plain title marlijn — a word that in Dutch stands for all marlins. Read “marlijn” there and you cannot tell which one is meant.
  • “Aguja negra”, “picudo negro”. GBIF also lists it in Spanish as aguja negra and picudo negro. But in Spanish aguja also stands for the garfish, to which this series devotes a group of its own — a fish of barely a metre, unrelated to the marlins.

That leaves the question every article in this series starts with: when. Habitat, prey and habits are set out above, and they are fixed. Everything else changes every day — and that is exactly where it is decided whether a day on the water is worth it. That is what StrikeAhead works out: it takes the conditions on your water and tells you when the trip is worth it. And because you cannot read reef edges, baitfish schools and the blue of the open sea from day one, StrikeAhead Pathfinder tells you who to go out with: curated guides and skippers, personally vetted before listing — licence and insurance —, with verified catches instead of promo photos, no paid ranking and, for you as an angler, no booking fee.

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