Description & Behavior

Black marlins, Istiompax indica (Cuvier, 1832), aka black marlin fishes, black-marlins, giant black marlins, marlins, Pacific black marlins, short nosed sword fishes, silver marlins, silver marlin fishes, and swordfishes, are a strong, fast pelagic species highly prized by sport fishermen (and possibly the fastest fish in the ocean reaching speeds of up to 129 kph or 80 mph). They have a dark blue dorsal (upper) side, a silvery-white belly and faint blue vertical stripes running down their sides. Their first dorsal fin is blackish to dark blue, while their other fins are dark brown, occasionally with blue tinges. They may have anywhere between 39 and 50 dorsal soft rays. Males may reach a length of 4.65 m and weight of 750 kgs, but females are generally much larger. The black marlin is the only marlin with non-retractable fins. Like all billfishes, this species has a distinctive elongated sword-like upper jaw. The black marlin’s dorsal fin is proportionately the lowest of any billfish, standing less than 50 percent of the fish’s body height. Scientists do not yet know how long members of this species live.

World Range & Habitat

A highly migratory species, black marlins, Istiompax indica, are usually found in shallow waters above the thermocline at 15 to 30° C, near shore close to continents, islands and coral reefs. Their depth ranges from 0 to 915 m, though they rarely swim below 30 m. In the Indo-Pacific, they inhabit both tropical and subtropical waters, occasionally entering temperate waters, but generally staying between 40° N and 45° S. Stray individuals may migrate into the Atlantic Ocean by way of the Cape of Good Hope, but no breeding populations appear to be permanent residents in the Atlantic.

Feeding Behavior (Ecology)

Black marlins feed on dolphinfish, squid, cuttlefish, octopuses, mackerels, trevallies, swordfish, and large decapod crustaceans, but prefers small tunas when abundant. Stomach analysis indicates that these fish use their long, sharp bills to slash their prey.

Life History

Black marlins spawn by external fertilization in water temperatures around 27 or 28° C. A single pregnant female may carry up to 40 million eggs.

Conservation Status & Comments

Black marlins have not yet been evaluated as to whether they are a threatened or endangered species. Their flesh is marketed refrigerated or frozen in the United States and prepared as sashimi in Japan. However, they are banned in parts of Australia for their high selenium and mercury content.

Resilience to fishing pressure: Medium, minimum population doubling time 1.4 – 4.4 years
Extinction vulnerability to fishing: Moderate vulnerability (44 of 100)

References & Further Research

Black Marlin, Makaira indica (Cuvier, 1832) – Australian Museum
Makaira indica, Black marlin – Australian Fisheries Resources, 1993

Research Istiompax indica @
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