401 



Abstract — Behavior of young (8-18 

 mm SL) giant trevally (Caranx igno- 

 bills), a large coral-reef-associated 

 predator, was observed in the labo- 

 ratory and the ocean. Size was a 

 better predictor of swimming speed 

 and endurance than was age. Critical 

 speed increased with size from 12 to 40 

 cm/s at 2.7 cm/s for each mm increase 

 in size. Mean scaled critical speed was 

 19 body lengths/s and was not size 

 related. Swimming speed in the ocean 

 was 4 to 20 cm/s (about half of criti- 

 cal speed) and varied among areas, 

 but within each area, it increased at 

 2 cm/s for each mm increase in size. 

 Swimming endurance in the labora- 

 tory increased from 5 to 40 km at 

 5 km for each mm increase in size. 

 Vertical distribution changed onto- 

 genetically: larvae swam shallower, 

 but more variably, and then deeper 

 with growth. Two-thirds of indi- 

 viduals swam directionally with no 

 ontogenetic increase in orientation 

 precision. Larvae swam offshore off 

 open coasts, but not in a bay. In situ 

 observations of C. ignobilis feeding, 

 interacting with pelagic animals, and 

 reacting to reefs are reported. 



Behavioral ontogeny in larvae and 

 early juveniles of the giant trevally 

 {Caranx ignobilis) (Pisces: Carangidae) 



Jeffrey M. Leis' 



Amanda C. Hay' 



Domine L. Clark' 



l-Shiung Chen^ 



Kwang-Tsao Shao^ 



' Ichthyology, Australian Museum 

 6 College Street 



Sydney, New South Wales 2010, Australia 

 E-mail address (for J. M. Leis); |effi@austmus.gov au 



2 National Museum of Marine Biology & Aquarium 

 2 Houwan Road 

 Checheng, Pingtung, 944, Taiwan 



^ Institute of Zoology, Academia Sinica 

 Academia Road 

 Nankang, Taipei, 115, Taiwan 



Manuscript submitted 16 December 2004 

 to the Scientific Editor's Office. 



Manuscript approved for publication 



27 September 2005 by the Scientific Editor. 



Fi.sh. Bull. 104:401-414 (20061. 



The giant trevally (known as ulua 

 aukea in Hawaii) (Caranx ignobilis 

 (ForsskaD), is the largest species in 

 the commercially important family 

 Carangidae. It has a wide tropical 

 Indo-Pacific distribution ranging from 

 Japan to Australia and from East 

 Africa to the Hawaiian and Mar- 

 quesas Islands (Randall et al., 1997; 

 Smith-Vaniz, 1999; Hoese et al., in 

 press). Adults of this reef-associated 

 pelagic species may be solitary or form 

 schools On inner reefs, inshore on sand 

 flats, or in reef channels, but primar- 

 ily on seaward reefs to depths of 80 

 m (Kuiter, 1993; Myers, 1999; Hoese 

 et al., in press). Caranx ignobilis is 

 an important top-level carnivore in 

 reef systems: adults and juveniles 

 feed during the day primarily on 

 demersal and pelagic fishes and to 

 a lesser extent on cephalopods and 

 crustaceans (Blaber et al., 1983; Sude- 

 kum et al., 1991; Myers, 1999). Adult 

 coloration varies from silver grey to 

 almost black above and fins are usu- 

 ally dark grey to black, but in small 

 juveniles the body is barred (pale to 

 dark gray) and the anal and caudal 

 fins are yellow (Kuiter, 1993; Ran- 

 dall et al., 1997). Caranx ignobilis is 

 important to commercial and recre- 

 ational fisheries and to aquaculture 



because of its size (maximum of 1.7 m 

 and 62 kg), abundance, palatability, 

 and reputation as an excellent game 

 fish (Smith-Vaniz, 1999; Yu, 2002). 

 The species can, however, be cigua- 

 toxic (Myers, 1999), 



Little is known of the early life 

 history of C. ignobilis. Adults, which 

 reach maturity at about 60 cm in 

 length and 3-4 years of age, have 

 been reported to gather on shallow 

 seaward reefs and offshore banks to 

 spawn (von Westernhagen, 1974; Jo- 

 hannes, 1981; Sudekum et al., 1991; 

 Myers, 1999). Neither eggs nor larvae 

 have been described, and nothing is 

 known of the distribution or behavior 

 of the larvae or early juveniles. Juve- 

 niles are found in small schools over 

 sandy inshore bottoms (Myers, 1999), 

 but also in turbid estuaries, where 

 they are "uncommon" (Blaber et al., 

 1983). Juveniles and subadults have 

 wide tolerances for salinity and tur- 

 bidity (Blaber et al., 1983). In Kaneo- 

 he Bay, Hawaii (a coral-reef lagoon 

 with estuarine features), C ignobilis 

 juveniles less than 20 cm (<1 year 

 old) were found on the "murky" lagoon 

 floor (Wetherbee et al., 2004). Juve- 

 niles were associated with lagoonal 

 patch reefs when they were between 

 25 and 40 cm in length, and appar- 



