As do all crustaceans, rock lobsters increase in size by moulting. Growth rate is a function of both moulting frequency and moult increment
Because techniques to allow lobsters to be aged are not yet reliable, growth has been estimated from size-frequency distributions and ongoing tag, release and recapture studies across most rock lobster management areas.
Estimates of the growth rates for small J. edwardsii are available from the Gisborne area and Stewart Island.
- Males and females in Gisborne both reach about 38 mm carapace length (CL) one year after settlement and about 58 mm CL after two years.
- At Stewart Island, after one, two and three years they have reached 33 mm, 52 mm, and 68 mm CL respectively.
Growth rates of larger J. edwardsii have been estimated for a number of areas. The estimates of growth per moult, moult frequency, and annual growth vary between areas and also between the sexes for the same area.
In most areas moulting is seasonal, with immature and mature animals of both sexes having their own distinct periods, which may vary between areas.
Smaller males (between about 70 mm and 80 mm CL) from most areas generally moult twice a year. Large males moult once each year; very large males may moult even less often.
Information on the growth rate of S. verreauxi is limited mainly to specimens between 120 mm and 159 mm CL. Males and females between 120 mm and 139 mm CL moult at least once a year, between July and November, and perhaps twice, with an increment of about 7 mm CL per moult.
Specimens between 140 mm and 159 mm CL moult once a year between July and November, with an average increment of about 6.8 mm and 6.0 mm CL for males and females respectively.