Yellow Jack - Biology

Biology

Yellow jack are predatory fish, moving both individually or in small groups, with their main prey being small fish, although observational records also show smaller benthic prey is taken. Yellow jack have been observed in a 'following role', moving around with larger species to take advantage of the commotion caused by the bigger fish, allowing the jack to opportunistically forage or take scraps left by the larger fish. As well as other teleosts, yellow jack have also been recorded following eels, stingrays and nurse sharks. In one case, they were observed following a flying gurnard, itself smaller than the jack, that disturbed the substrate, causing various organisms to be displaced and become available for predation. As well as being 'followers', larger specimens have also been observed as the 'followed' species. The species has also been observed living in close relationships with spinner dolphins, feeding off the dolphin's waste products. This behavior has also been observed in a number of other jacks living in the region.

Yellow jacks reach maturity at different times in different locations, with studies around Cuba showing males reach sexual maturity at 30 cm and females at 32 cm, while in Jamaica, males reach sexual maturity at 23 cm. Spawning takes place in offshore waters between February and October. Observational studies in Belize have shown that although courtship occurs in pairs, the species is a group spawner, congregating in large balls of around 300 fish, with spawning occurring mostly before sunset. Juveniles live near the surface of the ocean, often hiding amongst large mats of jellyfish or Sargassum weed, with a coloration that camouflages the fish in the weed. These young fish are often moved long distances by the Gulf Stream, and this is probably the process responsible for fish found as far north as Massachusetts.