Aspects of the reproductive biology and growth of Balmain bugs (Ibacus spp.) (Scyllaridae)

Abstract

This paper describes the reproductive biology and growth of Ibacus alticrenatus, I. brucei, and I. chacei from the east coast of Queensland, Australia. Reproductive cycles, sizes at maturity, sex ratios, morphological data, egg sizes, brood fecundities, length-frequency distributions, and growth parameters are described. Ibacus chacei numerically dominated both the commercial and research charter samples and were followed by I. brucei and I. alticrenatus in abundance respectively. Seasonal reproductive data indicated that I. brucei and I. chacei have an annual cycle of reproduction, with oviposition and hatching occurring earlier and over a shorter period in I. brucei. Gonadal maturation in ovigerous I. chacei suggested that more than one brood could be produced in a spawning season; however, reproductive activity was geographically restricted. Carapace lengths of ovigerous lobsters ranged 38.2-52.0 mm for I. alticrentatus, 44.6-69.7 mm for I. brucei, and 53.7-76.2 mm for I. chacei. Brood fecundity was size dependent and highest in I. brucei (2049-61,339) but markedly lower in I. chacei (2117-28,793) and I. alticrenatus (1734-14,762). Egg size in all three species was independent of carapace length, positively related to developmental stage, and ranged 0.94-1.29 mm for I. alticrentatus, 0.73-1.01 mm for I. brucei, and 1.02-1.37 mm for I. chacei. Monthly length-frequency distributions for I. chacei displayed marked multi-modality and indicated a prolonged recruitment period with moulting occurring 3-4 times within their first year post-recruitment. Growth curves of I. chacei indicated that females reach sexual maturity 1.7-2 yrs post settlement and that individuals approached their Lmax within 5-7 yrs. These results are discussed in relation to comparisons between each species and other members of the Scyllaridae family, and provide invaluable biological information for the development of sustainable management strategies for Queensland's Ibacus species.