Sudekum et al.: Life history and ecology of Caranx ignobihs and Caranx melampygus 



507 



of summed IRI), are among the more common reef 

 fishes in the NWHI (Parrish et al. 1985). No deep-water 

 or pelagic species were represented in the diet, which 

 suggests that C. melampygus associates closely with 

 shallow-water reefs. The relatively low incidence of 

 nocturnally active prey items suggests that this species 

 is primarily a diurnal or crepuscular feeder. Based on 

 their studies in the NWHI, Okamoto and Kawamoto 

 (1980) also believed that it feeds mostly diurnally. On 

 Hawaii Island, Hobson (1974) concluded that it prob- 

 ably feeds most often during early morning and late 

 afternoon. In southern Africa, van der Elst (1981) 

 stated that "while most active during early morning 

 and late afternoon, it also hunts at night." 



Little information is available on the diets of these 

 two Caranx species in Hawaii or elsewhere. Okamoto 

 and Kawamoto (1980) made the following brief, sum- 

 mary report, based on examination of the guts of 104 

 C. ignobilis and 27 C. melampygus from the NWHI: 

 "Stomach contents of (C ignobilis). . .included spiny 

 and slipper lobsters, shrimps, portunid crabs, octopuses 

 (Octopus cyanea and Octopus ornatus), eels, cornetfish, 

 squirrelfishes (family Holocentridae), and surgeon- 

 fishes. The omilu (C. melampygus) on the other hand, 

 was primarily a diurnal fish feeder with piha (Spratel- 

 loides delicatulus) comprising the bulk of its diet." 

 Small, incidental collections of C. melampygus guts at 

 South Kona (Hobson 1974, five specimens with prey) 

 and South Kohala (Parrish, unpubl. data, three speci- 

 mens with prey) on the west coast of Hawaii Island 

 contained fishes, shrimp, stomatopods, and mysids. 



Only fishes (including the serranid Anthias and a 

 carangid) were found in the guts of four C. melampygus 

 examined by Randall (1955) from the Gilbert Islands 

 and two specimens examined by Hiatt and Strasburg 

 (1960) from the Marshall Islands. Randall (1980) also 

 reported on fish prey in the guts of 44 specimens of 

 C. melampygus from the Marshall Islands, Hawaiian 

 Islands, Line Islands, Marcus Island, Solomon Islands, 

 and the Red Sea. Prey groups included eels, Caracan- 

 thidae, Serranidae (Anthias spp.), Priacanthidae, 

 Carangidae, Caesionidae, Mullidae, Pomacentridae, 

 Cirrhitidae, Labridae, Gobiidae, Acanthuridae, and 

 squid. He also found food in the guts of seven speci- 

 mens of C. ignobilis from the Marshall Islands, Line 

 Islands, Hawaiian Islands, Pitcairn Group, and the 

 Marquesas (Randall 1980). Prey included Scorpaenidae, 

 Scaridae, and Acanthuridae. 



Off east Africa, Williams (1956, 1965) reported only 

 the percent of C. ignobilis specimens that contained 

 each prey category (frequency percent) from 170 speci- 

 mens that contained identifiable prey. His results in- 

 cluded eels (0-2%), Synodontidae (0-1%), Plotosidae 

 (0-1%), Belonidae (Tylosurus sp.) (1-2%), Atherina sp. 

 (1-2%), Carangidae (0-2.5%), Leiognathidae (0-1%), 



Sphyraenidae (0-1%), Scaridae (2.5-6%), Siganus sp. 

 (1-2%), Monacanthidae (0-1%), Tetraodontidae 

 (0-1%), shrimp (0-2%), stomatopods (including Squilla 

 sp.) (6-10%), and cephalopods (including squid) 

 (2.5-4%). Including many unidentified prey groups, 

 79-84% of C. ignobilis contained fish, and at least 12% 

 contained crustaceans. Similar analysis of 89 C. melam- 

 pygus specimens containing prey (Williams 1956, 1965) 

 indicated the following frequency percent for prey 

 categories: Holocentridae (0-3%), Scorpaenidae 

 (0-2%), Caesio spp. (2-13%), Lutjanidae (including Lut- 

 janus sp.) (2-3%), Mullidae (0-2%), Labridae (0-2%), 

 Scaridae (5-7%), and stomatopods (0-2%). Altogether, 

 97-100% of these specimens contained fish (many 

 unidentified). 



Based on all available results, the diets of both 

 Caranx species appear to be strongly dominated by 

 fishes; C. melampygus was considerably more limited 

 to fishes in our study. Both jacks ate a wide variety 

 of species and ecological types of fishes. In both, the 

 labrids, scarids, mullids, and priacanthids were among 

 the most important prey, and pomacentrids and 

 monacanthids were at least moderately abundant. All 

 these families except monacanthids were reported in 

 the earlier studies of the diet of C. melampygus. 



Scarids occurred more widely and abundantly in the 

 diets than any other fish family. This result may be 

 biased by the ease of identifying scarid dental plates 

 among digested fish remains. No scarids could be iden- 

 tified to lower taxa. Scarids may be somewhat more 

 important to C. ignobilis. Labrids were important by 

 all measures in our study (especially for C. melampygus) 

 but less prominent in the reports of others. Eels were 

 rather widely reported in the diets of both species. At 

 least two eel families were represented in each species 

 in our studies (a total of three eel families). Their con- 

 siderable abundance in C. ignobilis suggests frequent, 

 active feeding close around reef structures or other 

 substrates that provide good cover. Seven C. ignobilis 

 individuals in our study contained more than one eel 

 each; one contained both a muraenid and a congrid eel. 



Monacanthids probably are taken commonly by these 

 jacks when monacanthid densities are normal. How- 

 ever, the heavy consumption indicated by our data is 

 probably a result of an unusual population explosion 

 of the filefish Pervagor spilosoma that occurred 

 during the course of the study. The monacanthids in 

 C. ignobilis were not further identifiable, but 24 of 28 

 monacanthid individuals in C. melampygus were iden- 

 tified as P. spilosoma and the other four as the genus 

 Pervagor. Fourteen of the 15 incidents of predation 

 (involving 27 of 28 prey individuals) occurred between 

 late June 1982 and late March 1983 (when field work 

 ended). These incidents began with the first sizable 

 collections of jacks after the surge in the filefish 



