ABSTRACT
This chapter summarizes the current knowledge of the fisheries and biology of four commercially exploited species of Ibacus (I. alticrenatus Bate, 1888, I. brucei Holthuis, 1977, I. chacei Brown & Holthuis, 1998, and I. peronii Leach, 1815) in Australia. These species are caught mostly off eastern Australia as by-product of demersal trawling, with annual landings (total for all species) of approximately 200 metric tons. Details are given for reproductive cycles, sizes at maturity, sex ratios, morphological data, mating, egg sizes, brood fecundities, egg-incubation periods, length-frequency distributions, molting, growth, movement, and life-history strategies. As I. chacei and I. peronii account for more than 95% of all Ibacus landed, the majority of current information is centered on these two species. Although there is considerable interspecies variation in relation to specific biological data, there are biological similarities among the four commercial species. Females grow to a larger size and reach sexual maturity at a larger size than males. Spawning occurs during the cooler months, with hatching occurring in spring/summer. Egg-incubation times range from two to four months, before hatching into larvae. Larvae develop through six to eight stages over two to four months before metamorphosing into a transparent nisto larva that does not feed. Nistos subsequently molt into juveniles. Growth rates do not vary until sexual maturity has been reached after four to six molts. The compilation of this chapter has highlighted that more research is required in order to sustainably manage the commercial exploitation of these species, and particular attention should focus on estimating mortality rates for use in egg- and yield-per-recruit modeling.
