Makaira nigricans, the game fish Ernest Hemingway made famous

Description

The blue marlin's body is cobalt blue on top, with a silvery white belly, and there may be light blue or lavender vertical stripes on the sides. It possesses a long bill that is very stout and round in cross section, with a conspicuous elevated nape (the part of neck posterior to the head). Small, file-like teeth line both jaws and the roof of its mouth. The dorsal fin is high and pointed anteriorly (rather than rounded) and its greatest height is less than the greatest body depth. The anal fin is relatively large, and it too is pointed. Built for speed, the blue marlin can fold its first dorsal, first anal, and pectoral fins down into fin grooves on the body to increase streamlining. The average weight of a blue marlin is 275-400 pounds, and the average length is 5.5-10 feet. Females are significantly larger than males, with some specimens reaching 1,985 pounds and 14 feet.

Distribution and Habitat

Blue marlin are found year-round in tropical oceanic waters of the Atlantic and Indo-Pacific. The range expands into temperate waters of the northern and southern hemispheres during the warmer months and contracts towards the equator during colder months. In the Atlantic Ocean, its range extends from around 40-45° N to 40° S in the western Atlantic, but it is absent from the Mediterranean Sea. In the Pacific, its range extends from about 45° N to 35° S. In the Indian Ocean, its range extends to 45° S. The largest numbers are usually found in waters warmer than 75° F, but blue marlin have been found at surface water temperatures as high as 87° F and as low as 71° F.

Blue marlin are so-called blue-water fish, spending most of their lives far out at sea. They are also highly migratory, and will follow warm ocean currents for hundreds and even thousands of miles.

Diet

An apex predator, blue marlin hunt during the daytime, rarely gathering in schools, preferring to hunt alone. Often, it approaches a school of fish or invertebrates at full speed, slashes through with its bill, then returns to devour the stunned or dead prey. It forages mostly in the near-surface waters, but also feeds near the bottom. A variety of fish, mollusks, and crustaceans are taken. The numbers and types of species consumed vary, depending on the location and season.

Reproduction

Spawning season extends from July through October in the North Atlantic. In the South Atlantic, the blue marlin exhibits fall spawning when the sea surface temperature is at about 82° F. In the Pacific Ocean, spawning occurs from December to January, during the southern hemisphere's summer. Females can spawn up to four times during the reproductive season, while males can spawn year round.

Little else is known about the mating habits of blue marlin, except that the eggs are fertilized externally. The eggs are spherical, transparent, white to yellow in color, and around 1 mm in diameter. They are bouyant in the water and drift until hatching with no parental care.

Blue marlin reach sexual maturity at 2-4 years. Females can live up to 30 years, while males rarely live more than 18 years.

Other Information

The blue marlin propels itself with its caudal fin and displaces water with side to side movements, similar to a shark. It follows a straight or slightly curving course when swimming. Typically, it travels at low speeds of around 1-2 mph for long periods, which are punctuated by short bursts of rapid speed associated with descents down the water column. As a continuous swimmer, it can cover 25-45 miles in a day.

Some taxonomists believe that the Atlantic and Pacific blue marlins are closely related but separate species, while others treat the two populations as subspecies.

Although not currently endangered, conservationists worry that blue marlin are being unsustainably fished, particularly in the Atlantic.

It is a blue marlin that the fisherman battles in Ernest Hemingway's classic novella The Old Man and the Sea.

Scientific Classification

phylum Chordata
subphylum Vertebrata
superclass Osteichthyes
class Actinopterygii
order Percifornes
family Istiophoridae
genus & species Makaira nigricans

SOURCES
Animal Diversity Web animaldiversity.org
International Game Fish Association www.igfa.org
MarineBio Conservation Society marinebio.org
National Geographic animals.nationalgeographic.com

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This page was last updated on May 19, 2017.