Crevalle jack

The crevalle jack inhabits both inshore and offshore waters to depths of around 350 m, predominantly over reefs, bays, lagoons and occasionally estuaries.

Dietary shifts with both age, location and season have been demonstrated, which led some researchers to postulate the species is indiscriminant in its feeding habits.

The species is considered of good to poor quality table fare, and is sold fresh, frozen, or preserved, or as fishmeal or oil at market.

It was described and named in 1766 by the famed Swedish taxonomist Carl Linnaeus, based on the holotype specimen taken off the coast of the Carolinas, United States.

The former was an attempt to separate the 'subspecies' on each side of the Americas,[8] while the latter was an unnecessary name to divide the Atlantic Caranx hippos into subspecies.

These swellings were initially thought to be due to a copepod parasite, however radiographs and subsequent sectioning found them to be bony in nature.

The cause of this calcified connective tissue is still unknown, and there remains only a single reported case of such an ailment in crevalle jack.

[13] The crevalle jack's colour ranges from brassy green to blue or bluish-black dorsally, becoming silvery white or golden ventrally.

[6] In the western Atlantic, the southernmost record comes from Uruguay, with the species ranging north along the Central American coastline, and throughout the Caribbean and many of the numerous archipelagos within.

[3] The species distribution overlaps that of the similar longfin crevalle jack in the eastern Atlantic, with careful identification needed to distinguish the two.

[3] The crevalle jack lives in both inshore and offshore habitats, with larger adults preferring deeper waters than juveniles.

[18] Studies in West Africa found marked differences in the sex ratios of populations in brackish waters, with females very rarely seen in such environments once they are mature.

[19] Adults that move offshore generally do not leave continental shelf waters, however still penetrate to depths of 350 m,[10] and possibly deeper.

[20] Adults have also been sighted around the large oil rig platforms throughout the Gulf of Mexico, where they use the man-made structure like a reef to hunt prey.

[21] The larvae and young juveniles of the species live pelagically offshore along the continental shelf and slope, and are also known to congregate around oil platforms, as well as natural floating debris such as sargassum mats.

In North America, young individuals recruited to northern estuaries are known to move to warmer tropical waters at the onset of winter to escape possible hypothermia.

[25] This applies not only to river dwelling fish, but also to marine migrants which linger too long in the temperate regions during winter.

DMSP is a naturally occurring chemical produced by marine algae and, to a lesser extent, corals and their symbiotic zooxanthellae.

[27] The percentage of various invertebrates also was highly variable, with penaeid shrimps, portunid crabs, stomatopods and squid being of importance to different populations.

The study also indicated young crevalle jack predominantly take clupeids, adding sparids and later carangids to their diets as they grow larger.

[27] This general change in diet with age also seems spatially variable, with young crevalle jack in both Maryland and Puerto Rico consuming almost exclusively crustaceans, including shrimps, crabs (and juvenile tarpon) in Maryland[28] and harpacticoid copepods in Puerto Rico before moving to fish-dominated diets later in life.

[29][30] The diets of the populations in both the southern USA and Ghana also varied quite markedly by season and year, which led the authors of both these studies to agree with these earlier conclusions.

[19] During some feeding periods recorded in Ghana, digestion in the species was so rapid that food becomes unidentifiable within four to five hours of consumption.

[6] As well as being preyed on during its adult stage, the spawn of the crevalle jack is known to be eaten by planktivorous organisms, including whale sharks in the Caribbean.

South of Florida, this period is between March and September,[33] in Cuba it is April and May,[6] while in Jamaica no definitive peak has yet been identified.

[33] Otolith and vertebrae studies have proved useful in determining the age and thus growth patterns of the species, with other methods including scale and fin ray sectioning having lesser value.

[38] While the young juveniles live in the exposed pelagic environment, they use a behaviour called 'piloting' to swim in very close proximity to both larger animals and floating objects, such as sargassum mats, buoys and even boats.

[39] By the time juveniles make their way to shore, they may have been dispersed large distances from their initial spawning grounds and may face the challenge of migration to warmer climates during winter if they are to survive as outlined previously.

[42] Fishermen often target regions where depth suddenly changes, such as channels, holes, reefs or ledges, with strong currents and eddies favourable.

[43] Crevalle jack are generally considered quite poor table fare, with selection of younger fish and bleeding upon capture giving the best results.

Several crevalle jacks over a reef in Florida
watercolor of a Caranx hippo
19th century watercolor of a Caranx hippos by Jacques Burkhardt
Crevalle jacks swimming in the Georgia Aquarium
A school of crevalle jack swarming around a Caribbean reef shark