Maturation of the male giant crab, Pseudocarcinus gigas, and the potential for sperm limitation in the Tasmanian fishery

Abstract

The onset of sexual maturity of male giant crabs (Pseudocarcinus gigas) from Tasmania, Australia was assessed to determine the extent of protection of mature males provided by the minimum legal catch size of 150 mm carapace length (CL). Maturity was assessed by morphometric analysis of chela development, change in vaso-somatic index (VSI) with size and production of spermatophores. Males develop through three morphological groups based on development of the molariform chela relative to CL, termed `small-chela', `intermediate-chela', and 'large-chela'. The onset of morphological change to intermediate-chela occurs at approximately 120 mm CL at both sample sites (eastern and western Tasmania). Males with small-chela morphology were able to produce spermatophores and the mid vas deferens of all animals greater than 90 mm CL contained numerous well-formed spermatophores. Vaso-somatic index increases with CL, particularly for small-chela animals. Tank trials demonstrated that female giant crabs carry broods in successive years without moulting and stored sperm remains viable for at least four years under these conditions. Observation of functional maturity of males is required to fully assess the potential for sperm limitation in the fishery. Nonetheless, factors that appear to reduce the risk of sperm limitation include: both females and males are harvested; females do not moult every year thereby raising the operational sex ratio; and females can store sperm for extended periods.