Aspects of the biology of Caranx bucculentus (Teleostei: Carangidae) from the Gulf of Carpentaria, Australia

Abstract

Caranx bucculentus is the most abundant secondary consumer and the most important predator of commercially important penaeids in the Gulf of Carpentaria. More than 18 000 individuals of this species were collected from 406 trawls during 13 cruises in the Gulf of Carpentaria from 1986 to 1991. The species was most abundant in coastal waters, with a maximum biomass at a depth of 28.1 m. Catches were higher in prawn-trawling grounds than elsewhere in the gulf, and prawns comprised a greater proportion of the diet than is the case for other predatory fishes. Interannual variations in biomass occurred, but there were no differences between cruises or seasons. The decreased catches at night may have resulted from vertical die1 migration of C. bucculentus. Sexual maturity is reached at 110 mm standard length and about one year of age, which is much younger than in congeners. Back-calculated birth dates of C. bucculentus show year-round recruitment that peaks in the pre-wet season months of spring, and gonadosomatic index values are generally higher in the pre-wet season than in the wet season. Gonadosomatic index values remain relatively high (> 1.0), which indicates continuous spawning by C. bucculentus in the gulf. Other large tropical species of Caranx spawn annually, in summer. C. bucculentus fecundities range from 18 000 eggs for a 120-mm fish to about 650 000 eggs for a 460-mm fish. A possible switch is seen in the sex ratio-males seem to predominate at smaller sizes, whereas females seem to predominate among bigger fish. MULTIFAN length-frequency analysis gave values of L_∞ = 538.8 mm (8 years old) and K= 0.305 year ^-1. A growth rate of 822 mm year^-1 at L_∞/2 is comparable to the growth rates of other tropical carangids. The diet of C. bucculentus throughout the gulf is dominated by epibenthic crustaceans and teleosts.