Moult increments and frequency in the freshwater crayfish, Euastacus spinifer "(Decapoda: Parastacidae)", from the Sydney Region, Australia

Euastacus spinifer mark-recapture data have been used to investigate relationships of moulting frequency and moult increments to biological or environmental factors. Small individuals (20-35mm CL) usually moult three times per year (total frequency range 1-6); the medium size class (35-55mm CL) typically moults twice (total frequency range 1-3); large specimens (>55mm CL) moult once per year. No differences have been detected in annual frequencies related to sex or site and it is suggested that moulting is independent of sex and state of maturity. Moulting seasons for small and medium E. spinifer of both sexes are similar but trends for large females and males differ. Moulting activity in the small class commences in September or October and declines in April or May; the medium size class exhibits two periods of activity (October-November, February-May). Large females moult from March to June (with a peak of activity in May); large males moult from November to January. Temperature appears to be the prime environmental regulator of growth and moulting activity at all sizes usually only occurs when water temperatures exceed 14-15°C. No significant differences in moult increment have been detected between immature females, normal males or precocious males nor have any differences been found between season or location. Increments of mature females are smaller than males of comparable size and reproduction is considered to decrease increment size in females but not in males. Considerable increment variation, at both individual and populational levels, was detected. Food availability and population density are suggested as factors contributing to this variation. Analyses demonstrated an increase in moult increment with rising pre-moult carapace length in the range of 20-55mm, but above this size increments become constant.