745 



Abstract— Par tun us pelagicus was 

 collected at regular intervals from two 

 marine embayments and two estuaries 

 on the lower west coast of Australia 

 and from a large embayment located 

 approximately 800 km farther north. 

 The samples were used to obtain data 

 on the reproductive biology of this 

 species in three very different envi- 

 ronments. Unlike females, the males 

 show a loosening of the attachment 

 of the abdominal flap to the cephalo- 

 thorax at a prepubertal rather than a 

 pubertal molt. Males become gonadally 

 mature (spermatophores and seminal 

 fluid present in the medial region of 

 the vas deferentia) at a very similar 

 carapace width (CW) to that at which 

 they achieve morphometric maturity, 

 as reflected by a change in the relative 

 size of the largest cheliped. Logistic 

 curves, derived from the prevalence 

 of mature male P. pelagicus, gener- 

 ally had wider confidence limits with 

 morphometric than with gonadal data. 

 This presumably reflects the fact that 

 the morphometric (allometric) method 

 of classifying a male P. pelagicus as 

 mature employs probabilities and is 

 thus indirect, whereas gonadal struc- 

 ture allows a mature male to be read- 

 ily identified. However, the very close 

 correspondence between the CWj^'s 

 derived for P. pelagicus by the two 

 methods implies that either method 

 can be used for management purposes. 

 Portunus pelagicus attained maturity 

 at a significantly greater size in the 

 large embayment than in the four 

 more southern bodies of water, where 

 water temperatures were lower and the 

 densities of crabs and fishing pressure 

 were greater. As a result of the emigra- 

 tion of mature female P. pelagicus from 

 estuaries, the CWj^'s derived by using 

 the prevalence of mature females in 

 estuaries represent overestimates for 

 those populations as a whole. Estimates 

 of the number of egg batches produced 

 in a spawning season ranged from one 

 in small crabs to three in large crabs. 

 These data, together with the batch 

 fecundities of different size crabs, indi- 

 cate that the estimated number of eggs 

 produced by P. pelagicus during the 

 spawning season ranges from about 

 78,000 in small crabs (CW=80 mm) 

 to about 1,000,000 in large crabs 

 (CW=180 mm). 



Manuscript approved for publication 

 19 June 2003 by Scientific Editor. 



Manuscript received 26 June 2003 at 

 NMFS Scientific Publications Office. 



Fish. Bull. 101:745-757 (2003). 



Reproductive biology of the blue swimmer crab 

 (Portunus pelagicus, Decapoda: Portunidae) in 

 five bodies of water on the west coast of Australia 



Simon de Lestang 



Norman G. Hall 



Ian C. Potter 



Centre for Fish and Fisheries Research 



Division of Science and Engineering 



Murdoch University 



South Street 



Murdoch, Western Australia 6150 



E-mail (for S de Lestang): simond@murdoch edu.au 



Portunid crabs, such as Portunus pelagi- 

 cus, Scylla serrata, and Callinectes sapi- 

 dus, form the basis of important 

 commercial and recreational fisheries. 

 The blue swimmer crab (P. pelagicus) 

 is found in sheltered nearshore marine 

 waters and estuaries throughout the 

 Indo-West Pacific (Stephenson, 1962; 

 Kailola et al., 1993). In Australia, the 

 commercial catches of this portunid 

 have increased greatly during the last 

 20 years, and annual catches in 1998 

 reached 4377 metric tons (t) (Anony- 

 mous, 2000). The commercial fishery 

 for P. pelagicus in Western Australia 

 is the largest in Australia; the catch in 

 the 1999-2000 financial year weighed 

 673 t and fetched a wholesale price of 

 approximately $A3 million fCAES^). 



Large numbers of portunids fre- 

 quently enter estuaries as juveniles 

 and remain there for an extended 

 period (Hill, 1975; Potter et al., 1983; 

 Perkins-Visser et al., 1996; Potter and 

 de Lestang, 2000). Although female 

 portunids sometimes become ovigerous 

 in estuaries, such individuals emigrate 

 into coastal marine waters, where they 

 release their eggs (Van Engel, 1958; 

 Metcalf et al., 1995; Potter and de Les- 

 tang, 2000). In contrast, the individuals 

 of those assemblages of portunids that 

 occupy marine embayments often do 

 not leave these marine environments 

 to spawn and, in cases where there is 

 a salinity gradient, they spawn in the 

 high salinity regions of those systems 

 (e.g. Campbell, 1984; Sumpton et al., 

 1994; Prager, 1996; Potter and de Les- 

 tang, 2000). 



The most common method for deter- 

 mining the size at which male crabs at- 

 tain maturity is to estimate the size at 

 which the pattern of growth of one of 

 its appendages changes from that which 

 characterizes juvenile crabs to that 

 which characterizes adult crabs (e.g. 

 Hartnoll, 1974; Somerton, 1980; Reeby 

 et al., 1990; Muino et al., 1999). Howev- 

 er, this indirect approach is not precise 

 and requires careful measurements of 

 a considerable number of individuals 

 covering a wide size range. Despite the 

 fact that macroscopic characters can be 

 used to distinguish sequential stages in 

 the development of the vas deferentia 

 of portunids (Ryan, 1967a; Meagher, 

 1971), few studies have attempted to 

 use such staging to determine the body 

 size at which the gonads of male crabs 

 attain maturity (e.g. Reeby et al., 1990). 

 Sumpton et al. (1994) considered that, 

 as in female P. pelagicus, a marked loos- 

 ening of the attachment of the abdomi- 

 nal flap to the cephalothorax signaled 

 the attainment of maturity in male 

 P. pelagicus. However, this criterion 

 has yet to be shown to be valid for the 

 males of this species. Although varia- 

 tions in the size at which crustaceans 

 reach maturity among bodies of water 

 and geographical regions may reflect, 



1 CAES (Department of Fisheries, Catch 

 and Effort Statistics). 2002. Unpubl. 

 data. Western Australian Department 

 of Fisheries, Catch and Effort Sta- 

 tistics. Fisheries Western Australia, WA 

 Marine Research Laboratories, West Coast 

 Drive, Waterman, 6020, Perth, Australia. 



