Bar Jack

The bar jack is a moderately large species, growing to a recorded maximum length of 69 cm (27 in), and a weight of 6.8 kg (15 lb), but is commonly encountered at lengths of less than 40 cm (16 in). The bar jack displays the typical body shape of most of the jacks, having an elongate, moderately deep and compressed form, with dorsal and ventral profiles of approximately equal convexity. The dorsal fin is divided into two sections, the first consisting of 8 spines while the second has 1 spine followed by 26 to 30 soft rays. The anal fin is composed of 2 anteriorly detached spines followed by 1 spine and 23 to 26 soft rays, with both the anal and soft dorsal fin lobes being slightly elongated. The pectoral fins are falcate and longer than the head, consisting of 19 to 21 soft rays. The lateral line is moderately arched anteriorly, and possesses 17 to 104 scales including 23 to 29 scutes posteriorly; also having bilateral paired caudal keels present. The chest is completely scaled, which easily distinguishes it from the similar crevalle jack, Caranx hippos. The snout is moderately pointed, with both the jaws containing narrow bands of villiform teeth, with the bands becoming wider anteriorly. The upper jaw also contains an outer row of enlarged recurved teeth. …

The bar jack is widely distributed throughout the tropical and subtropical waters of the western Atlantic Ocean, and is a common species throughout most of its range. The northernmost limit of its range is New Jersey in the northern United States, with its range extending south along the continental coast to Venezuela. It inhabits a number of offshore islands and archipelagos including Bermuda, as well as the West Indies. The bar jack is most abundant in the Gulf of Mexico, the West Indies and Caribbean, but in the Gulf of Mexico is limited to offshore waters. There have been reliable reports of the species from Rio de Janeiro in Brazil and far offshore at Saint Helena in the south central Atlantic, which would extend the species southern limit significantly if correct. The bar jack generally live in clear shallow water environments, predominantly around coral reefs to depths of around 60 ft (18 m). Tagging studies demonstrate the species is highly mobile, not lingering over one particular reef patch for very long, often moving between reefs over large expanses of sand. Bar jack often venture into lagoons from seaward reefs, preferring to move over the sandy substrate while in these shallow waters, often forming shoals alongside barracudas, stingrays and sharks. …

The bar jack is a benthopelagic predator, taking its prey both in midwater and along the seafloor. The diet consists mostly of fish, up to 90% of the fish's intake in some studies, with planktonic crustaceans and small cephalopods taken in minor volumes. There is significant change in diet with age in fish studied off Cuba, which may reduce intraspecific competition in the species. Young fish prefer planktonic organisms, predominantly decapod and fish larvae; fish reaching sexual maturity prey on shrimp and small fish, while mature fish feed almost exclusively on small fish. The fish species preferred by bar jack appear to be mostly small sand dwellers such as blennies and gobies or small reef dwellers including wrasses, butterflyfish and filefish, with the diet of the latter leading to the accumulation of coral derived ciguatera toxin in the jack's flesh. Other lesser taken prey items include gastropods, nematodes and benthic algae as well as a range of crustaceans. Feeding intensity varies throughout the year, and is strongly correlated to changes in the precipitation and wind during cyclical shifts in the climate. Young fish tend to feed intensively throughout the year, but show a peak in the spring and autumn months, while adults intensify their feeding during the dry and rainy seasons, with feeding declining during intermediate periods (winter and early summer). …