The crevalle jack, Caranx hippos (also known as the common jack, black-tailed trevally, couvalli jack, black cavalli and yellow cavalli) is a common species of large marine fish classified within the jack family, Carangidae.  The crevalle jack is distributed across the tropical and temperate waters of the Atlanta Ocean.  The crevalle jack inhabits both inshore and offshore waters to depths of around 350 m, predominantly over reefs,  bays, lagoons  and occasionally estuaries. Young fish dispersed north by currents in the eastern Atlantic are known to migrate back to more tropical waters before the onset of winter; however if the fish fail to migrate, mass mortalities occur as the temperature falls below the species tolerance limits.

A school of Big Jacks

The crevalle jack is a powerful predatory fish.  This is a school of big Jacks cruising through water ready to eat anything that gets in their way.  We use the motor to get close to the school.  Then we use the trolling motor to get in front of the fish.  When Capt. Dave puts the boat in the perfect position, you cast in front of the school, and hold on.  It is a thrill to watch 30 lb Jacks fight for your fly.  They are an aggresive and opportunistic feeder.

The crevalle jack is also a revered gamefish, taken both by lures and bait.

Summarized from Wikepedia.