Life history and ecology of large jacks in undisturbed, shallow, oceanic communities

The large jack species Caranx ignobilis and Caranx melampygus were collected from the nearly pristine shallow waters of the atolls, reefs, and shoals of the North-western Hawaiian Islands. Both species were aged by counting daily otolith increments and validating frequency of otolith deposition by marking captive fish with tetracycline. Growth for each species was well described by a von Bertalanffy relationship. Measured growth of captive C. melampygus was also in agreement. Gravid fish of both species were found only in April-November; peak spawning season for both was about May-August. Reproduction began at similar to 350 mm SL ( similar to 2 years old) in C. melampygus and at similar to 600 mm SL ( similar to 3-1/2 years old) in C. ignobilis . Fecundity of female C. melampygus varied approximately as the 1.7 power of body weight. Both species were > 90% piscivorous, as judged from combined volume and number of prey and incidence of predation. Crustaceans and cephalopods comprised several percent of the diet of C. ignobilis ; both groups were present but less important in C. melampygus . Both jack species ate gastropods in trace amounts.