De Lestang et al : Reproductive biology of Portunus pelagicus 



753 



20 



15 



'■ 

 30 



15 





 30 t 



Female crabs 



r-Th-T-r-n 



10 





 30 r 



15 



^ 

 30 



0' 

 30 



15 





 30 r 



Male crabs 



40 80 120 160 



Carapace width (mm) 



40 



80 



120 



160 



Figure 6 



Frequency histogi-ams for the carapace widths of juvenile and adult females and males 

 of Portunus pelagicus in Cockburn Sound, n = number of crabs measured. Designation of 

 males as mature was based on gonadal criteria described in the text. 



Age and time of sexual maturation of Portunus pelagicus 



The carapace-width frequency data for P. pelagicus in 

 inshore and offshore waters in Cockburn Sound demon- 

 strated that, in this marine embayment, males are repre- 

 sented by two main size cohorts in January and February 

 (Fig. 6). The first size cohort represents the 0+ age class 

 that resulted from the spawning period that commenced in 

 the previous August-September, whereas the second cohort 

 corresponds to l-i- crabs, which start to decline markedly in 

 numbers after February and are rarely represented after 



June (Fig. 6). Although similar trends are exhibited by the 

 data for females, the numbers of 1+ individuals of this sex 

 remained higher for a longer period, i.e. until May. The 

 above trends are entirely consistent with those reported 

 in detailed studies of the age composition and growth of 

 P. pelagicus in the Peel-Harvey Estuary (Potter et al., 1983) 

 and Leschenault Estuary (Potter and de Lestang, 2000). 



None or very few of the female and male 0+ crabs caught 

 in Cockburn Sound in January, February, and March were 

 mature. However, some of the larger 0-t- crabs had become 

 mature by May, i.e. when they would mostly have been 



