Atlantic blue marlin

The Atlantic blue marlin (Makaira nigricans) is a species of marlin endemic to the Atlantic Ocean. It is closely related to, and usually considered conspecific with, the Indo-Pacific blue marlin, then simply called blue marlin. Some authorities consider both species distinct. Blue marlin are distributed throughout the tropical and subtropical waters of the Atlantic Ocean. It is a bluewater fish that spends the majority of its life in the open sea far from land.

The blue marlin preys on a wide variety of marine organisms, mostly near the surface, often using its bill to stun or injure its prey then returning to eat the injured or stunned fish. Females can grow up to four times the weight of males. The maximum published weight is and length . Greater lengths have been claimed unofficially. Estimates of the maximum swimming speed of the blue marlin commonly go as high as 72 km/h, though the casual swimming speed at which it moves most of the time is under 4.5 km/h.

They are sought after as a highly prized game fish by anglers and are taken by commercial fishermen, both as a directed catch and as bycatch in major industrial tuna fisheries. Blue marlin are currently considered a threatened species by the IUCN due to overfishing, The relatively high fat content of its meat makes it commercially valuable in certain markets. It is the national fish of the Commonwealth of The Bahamas and is featured on its coat of arms.

Taxonomy and naming

The blue marlin is placed in the genus Makaira. This name is derived from the Greek word machaira, meaning "a short sword or bent dagger", and the Latin machaera, "sword".

The specific epithet nigricans is Latin for "becoming black".

The blue marlin is part of the billfish family Istiophoridae which is in the jack order Carangiformes. In addition, it is in the suborder Xiphioidei and is a member of the subclass Neopterygii, which means "new wings". It is also in the class of Actinopterygii, which includes ray-finned fishes and spiny-rayed fishes, and the superclass Osteichthyes, which includes all of the bony fishes.

The classification of the Atlantic blue marlin (M. nigricans) and the Indo-Pacific blue marlin (M. mazara) as separate species is under debate. Genetic data suggest, although the two groups are isolated from each other, they are both the same species, with the only genetic exchange occurring when Indo-Pacific blue marlin migrate to and contribute genes to the Atlantic population. A separate study by V. P. Buonaccorsi, J. R. Mcdowell, and Graves indicated that both Indo-Pacific and Atlantic show "striking phylogeographic partitioning" of mitochondrial and microsatellite loci.

Synonyms

Synonyms of M. nigricans are: The longest females can reach a length of with the bill, from eye to tip, constituting about 20% of the total body length.

Body mass in the largest female specimens has been reported from , depending on the source (few large specimens are scientifically verified). The largest blue marlin caught by IGFA angling rules is from Vitoria, Brazil, which weighed .; fishermen often refer to individual marlins that reach or exceed 1,000 pounds as "granders".

Both sexes have 24 vertebrae, of which 11 are precaudal and 13 are caudal.

The marlin has two dorsal fins and two anal fins. The fins are supported by bony spines known as rays. Its first dorsal fin has 39 to 43 rays from front to back.

Most often, however, the body is blue-black on top with a silvery white underside. It has about 15 rows of pale, cobalt-colored stripes, each of which has round dots and/or thin bars, located on both sides of the fish. It has the appearance of a net. It is obvious in immature specimens but unclear in adults, becoming progressively embedded in the skin. Warm currents, such as the Gulf Stream, in the western Atlantic have a major influence on their seasonal distribution.

Being the most tropic of all the billfishes, they spend a lot of time in the water column shifting from the top to a depth of 100 meters. They spend most nights near the surface and dive to deeper depths during the day. Limited from going any lower by the water temperature and oxygen levels.

The blue marlin's latitudinal range extends from about 45°N to about 35°S. It is less abundant in the eastern Atlantic, where it mostly occurs off Africa between the latitudes of 25°N and 25°S. The largest numbers are usually found in waters warmer than 24 °C (75 °F), but blue marlin have been found at surface water temperatures as high as 30.5 °C (86.9 °F) and as low as 21.7 °C (71.1 °F).

Tagging studies, using conventional "spaghetti" tags, and more recently pop-up satellite tags, have given researchers a glimpse into blue marlin migration patterns and habits. Recaptures of tagged fish have shown multiple movements between the Caribbean Islands and Venezuela and the Bahamas, as well as between the Caribbean Saint Thomas, U.S. Virgin Islands and West Africa, and interocean travel. Most notably, a blue marlin tagged off the coast of Delaware was recovered near the island of Mauritius off the southeast coast of Africa in the Indian Ocean – a voyage of 9,254 miles. Several fish have been recaptured in the same general area where they were tagged, implying reverse migration after/over several years, but the data are insufficient to accurately determine seasonality.

Predators and parasites

Once blue marlin reach maturity, they have few predators, with the most important being killer whales and large pelagic sharks, such as the shortfin mako and great white shark.

Blue marlin have many parasites, including from these groups: Digenea (flukes), Didymozoidea (tissue flukes), Monogenea (gillworms), Cestoda (tapeworms), Nematoda (roundworms), Acanthocephala (spiny-headed worms), copepods, barnacles, and cookiecutter sharks.

Lifecycle

Growth and maturity

Atlantic blue marlin reach sexual maturity at the age of two to four years. Males reach sexual maturity at a weight of and females at .

Blue marlin breed in late summer and fall. Females may spawn as many as four times in one season. They often release over seven million eggs at once, each about in diameter. Few reach sexual maturity. The planktonic young drift freely in the ocean's pelagic zone. Larvae inhabit the west central Atlantic off the Southern United States, Jamaica, The Bahamas, the Dominican Republic, and Puerto Rico, and also the southwest Atlantic off Brazil.

Bioaccumulation

Heavy metals have been known to accumulate in the Atlantic blue marlin, a process known as bioaccumulation. In 2017, the Texas Parks and Wildlife Department issued a consumption advisory for all blue marlin caught along the coast of Texas based on the presence of mercury.

Economic importance

thumb|An 8-oz (230-g) marlin steak|alt=Approximately triangular piece of pink-to-red fish

Commercial fishery

Marlin has commercial value throughout the world, with landings totalling 3,064 metric tons in 2000.

Sport fishermen have been at the forefront of efforts to conserve blue marlin populations. The initial efforts to develop electronic tags for tracking highly migratory fish were carried out on marlin in Hawaii, in collaboration with anglers in the Hawaiian International Billfish Tournament.