Moulting growth of the Australian giant crab, Pseudocarcinus gigas

Abstract

The growth of Australian giant crabs, Pseudocarcinus gigas, has not been previously studied. A tagging program was undertaken in four Australian states where the species is subject to commercial exploitation. Fishers reported a recapture sample of 1372 females and 383 males from commercial harvest, of which 190 females and 160 males had moulted at least once. Broad-scale modes of growth increment were readily identified and interpreted as 0 , 1 and 2 moults during time at large. Single-moult increments were normally distributed for six of seven data sets. Moult increments were constant with length for males and declined slowly for three of four female data sets. Seasonality of moulting in South Australia was inferred from monthly proportions captured with newly moulted shells. Female moulting peaked strongly in winter (June and July). Males moult in summer (November and December). Intermoult period estimates for P. gigas varied from 3 to 4 years for juvenile males and females (80–120 mm carapace length, CL), with rapid lengthening in time between moulting events to approximately seven years for females and four and a half years for males at legal minimum length of 150 mm CL. New moulting growth estimation methods include a generalization of the anniversary method for estimating intermoult period that uses (rather than rejects) most capture–recapture data and a multiple likelihood method for assigning recaptures to their most probable number of moults during time at large.